1 acpi= [HW,ACPI,X86,ARM64] 2 Advanced Configuration and Power Interface 3 Format: { force | on | off | strict | noirq | rsdt | 4 copy_dsdt } 5 force -- enable ACPI if default was off 6 on -- enable ACPI but allow fallback to DT [arm64] 7 off -- disable ACPI if default was on 8 noirq -- do not use ACPI for IRQ routing 9 strict -- Be less tolerant of platforms that are not 10 strictly ACPI specification compliant. 11 rsdt -- prefer RSDT over (default) XSDT 12 copy_dsdt -- copy DSDT to memory 13 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force" 14 are available 15 16 See also Documentation/power/runtime_pm.rst, pci=noacpi 17 18 acpi_apic_instance= [ACPI, IOAPIC] 19 Format: <int> 20 2: use 2nd APIC table, if available 21 1,0: use 1st APIC table 22 default: 0 23 24 acpi_backlight= [HW,ACPI] 25 { vendor | video | native | none } 26 If set to vendor, prefer vendor-specific driver 27 (e.g. thinkpad_acpi, sony_acpi, etc.) instead 28 of the ACPI video.ko driver. 29 If set to video, use the ACPI video.ko driver. 30 If set to native, use the device's native backlight mode. 31 If set to none, disable the ACPI backlight interface. 32 33 acpi_force_32bit_fadt_addr 34 force FADT to use 32 bit addresses rather than the 35 64 bit X_* addresses. Some firmware have broken 64 36 bit addresses for force ACPI ignore these and use 37 the older legacy 32 bit addresses. 38 39 acpica_no_return_repair [HW, ACPI] 40 Disable AML predefined validation mechanism 41 This mechanism can repair the evaluation result to make 42 the return objects more ACPI specification compliant. 43 This option is useful for developers to identify the 44 root cause of an AML interpreter issue when the issue 45 has something to do with the repair mechanism. 46 47 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] 48 acpi.debug_level= [HW,ACPI,ACPI_DEBUG] 49 Format: <int> 50 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI 51 debug output. Bits in debug_layer correspond to a 52 _COMPONENT in an ACPI source file, e.g., 53 #define _COMPONENT ACPI_EVENTS 54 Bits in debug_level correspond to a level in 55 ACPI_DEBUG_PRINT statements, e.g., 56 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... 57 The debug_level mask defaults to "info". See 58 Documentation/firmware-guide/acpi/debug.rst for more information about 59 debug layers and levels. 60 61 Enable processor driver info messages: 62 acpi.debug_layer=0x20000000 63 Enable AML "Debug" output, i.e., stores to the Debug 64 object while interpreting AML: 65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2 66 Enable all messages related to ACPI hardware: 67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff 68 69 Some values produce so much output that the system is 70 unusable. The "log_buf_len" parameter may be useful 71 if you need to capture more output. 72 73 acpi_enforce_resources= [ACPI] 74 { strict | lax | no } 75 Check for resource conflicts between native drivers 76 and ACPI OperationRegions (SystemIO and SystemMemory 77 only). IO ports and memory declared in ACPI might be 78 used by the ACPI subsystem in arbitrary AML code and 79 can interfere with legacy drivers. 80 strict (default): access to resources claimed by ACPI 81 is denied; legacy drivers trying to access reserved 82 resources will fail to bind to device using them. 83 lax: access to resources claimed by ACPI is allowed; 84 legacy drivers trying to access reserved resources 85 will bind successfully but a warning message is logged. 86 no: ACPI OperationRegions are not marked as reserved, 87 no further checks are performed. 88 89 acpi_force_table_verification [HW,ACPI] 90 Enable table checksum verification during early stage. 91 By default, this is disabled due to x86 early mapping 92 size limitation. 93 94 acpi_irq_balance [HW,ACPI] 95 ACPI will balance active IRQs 96 default in APIC mode 97 98 acpi_irq_nobalance [HW,ACPI] 99 ACPI will not move active IRQs (default) 100 default in PIC mode 101 102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA 103 Format: <irq>,<irq>... 104 105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for 106 use by PCI 107 Format: <irq>,<irq>... 108 109 acpi_mask_gpe= [HW,ACPI] 110 Due to the existence of _Lxx/_Exx, some GPEs triggered 111 by unsupported hardware/firmware features can result in 112 GPE floodings that cannot be automatically disabled by 113 the GPE dispatcher. 114 This facility can be used to prevent such uncontrolled 115 GPE floodings. 116 Format: <byte> or <bitmap-list> 117 118 acpi_no_auto_serialize [HW,ACPI] 119 Disable auto-serialization of AML methods 120 AML control methods that contain the opcodes to create 121 named objects will be marked as "Serialized" by the 122 auto-serialization feature. 123 This feature is enabled by default. 124 This option allows to turn off the feature. 125 126 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump 127 kernels. 128 129 acpi_no_static_ssdt [HW,ACPI] 130 Disable installation of static SSDTs at early boot time 131 By default, SSDTs contained in the RSDT/XSDT will be 132 installed automatically and they will appear under 133 /sys/firmware/acpi/tables. 134 This option turns off this feature. 135 Note that specifying this option does not affect 136 dynamic table installation which will install SSDT 137 tables to /sys/firmware/acpi/tables/dynamic. 138 139 acpi_no_watchdog [HW,ACPI,WDT] 140 Ignore the ACPI-based watchdog interface (WDAT) and let 141 a native driver control the watchdog device instead. 142 143 acpi_rsdp= [ACPI,EFI,KEXEC] 144 Pass the RSDP address to the kernel, mostly used 145 on machines running EFI runtime service to boot the 146 second kernel for kdump. 147 148 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 149 Format: To spoof as Windows 98: ="Microsoft Windows" 150 151 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead 152 of 2 which is mandated by ACPI 6) as the supported ACPI 153 specification revision (when using this switch, it may 154 be necessary to carry out a cold reboot _twice_ in a 155 row to make it take effect on the platform firmware). 156 157 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 158 acpi_osi="string1" # add string1 159 acpi_osi="!string2" # remove string2 160 acpi_osi=!* # remove all strings 161 acpi_osi=! # disable all built-in OS vendor 162 strings 163 acpi_osi=!! # enable all built-in OS vendor 164 strings 165 acpi_osi= # disable all strings 166 167 'acpi_osi=!' can be used in combination with single or 168 multiple 'acpi_osi="string1"' to support specific OS 169 vendor string(s). Note that such command can only 170 affect the default state of the OS vendor strings, thus 171 it cannot affect the default state of the feature group 172 strings and the current state of the OS vendor strings, 173 specifying it multiple times through kernel command line 174 is meaningless. This command is useful when one do not 175 care about the state of the feature group strings which 176 should be controlled by the OSPM. 177 Examples: 178 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent 179 to 'acpi_osi="Windows 2000" acpi_osi=!', they all 180 can make '_OSI("Windows 2000")' TRUE. 181 182 'acpi_osi=' cannot be used in combination with other 183 'acpi_osi=' command lines, the _OSI method will not 184 exist in the ACPI namespace. NOTE that such command can 185 only affect the _OSI support state, thus specifying it 186 multiple times through kernel command line is also 187 meaningless. 188 Examples: 189 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' 190 FALSE. 191 192 'acpi_osi=!*' can be used in combination with single or 193 multiple 'acpi_osi="string1"' to support specific 194 string(s). Note that such command can affect the 195 current state of both the OS vendor strings and the 196 feature group strings, thus specifying it multiple times 197 through kernel command line is meaningful. But it may 198 still not able to affect the final state of a string if 199 there are quirks related to this string. This command 200 is useful when one want to control the state of the 201 feature group strings to debug BIOS issues related to 202 the OSPM features. 203 Examples: 204 1. 'acpi_osi="Module Device" acpi_osi=!*' can make 205 '_OSI("Module Device")' FALSE. 206 2. 'acpi_osi=!* acpi_osi="Module Device"' can make 207 '_OSI("Module Device")' TRUE. 208 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is 209 equivalent to 210 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' 211 and 212 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', 213 they all will make '_OSI("Windows 2000")' TRUE. 214 215 acpi_pm_good [X86] 216 Override the pmtimer bug detection: force the kernel 217 to assume that this machine's pmtimer latches its value 218 and always returns good values. 219 220 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode 221 Format: { level | edge | high | low } 222 223 acpi_skip_timer_override [HW,ACPI] 224 Recognize and ignore IRQ0/pin2 Interrupt Override. 225 For broken nForce2 BIOS resulting in XT-PIC timer. 226 227 acpi_sleep= [HW,ACPI] Sleep options 228 Format: { s3_bios, s3_mode, s3_beep, s4_hwsig, 229 s4_nohwsig, old_ordering, nonvs, 230 sci_force_enable, nobl } 231 See Documentation/power/video.rst for information on 232 s3_bios and s3_mode. 233 s3_beep is for debugging; it makes the PC's speaker beep 234 as soon as the kernel's real-mode entry point is called. 235 s4_hwsig causes the kernel to check the ACPI hardware 236 signature during resume from hibernation, and gracefully 237 refuse to resume if it has changed. This complies with 238 the ACPI specification but not with reality, since 239 Windows does not do this and many laptops do change it 240 on docking. So the default behaviour is to allow resume 241 and simply warn when the signature changes, unless the 242 s4_hwsig option is enabled. 243 s4_nohwsig prevents ACPI hardware signature from being 244 used (or even warned about) during resume. 245 old_ordering causes the ACPI 1.0 ordering of the _PTS 246 control method, with respect to putting devices into 247 low power states, to be enforced (the ACPI 2.0 ordering 248 of _PTS is used by default). 249 nonvs prevents the kernel from saving/restoring the 250 ACPI NVS memory during suspend/hibernation and resume. 251 sci_force_enable causes the kernel to set SCI_EN directly 252 on resume from S1/S3 (which is against the ACPI spec, 253 but some broken systems don't work without it). 254 nobl causes the internal blacklist of systems known to 255 behave incorrectly in some ways with respect to system 256 suspend and resume to be ignored (use wisely). 257 258 acpi_use_timer_override [HW,ACPI] 259 Use timer override. For some broken Nvidia NF5 boards 260 that require a timer override, but don't have HPET 261 262 add_efi_memmap [EFI; X86] Include EFI memory map in 263 kernel's map of available physical RAM. 264 265 agp= [AGP] 266 { off | try_unsupported } 267 off: disable AGP support 268 try_unsupported: try to drive unsupported chipsets 269 (may crash computer or cause data corruption) 270 271 ALSA [HW,ALSA] 272 See Documentation/sound/alsa-configuration.rst 273 274 alignment= [KNL,ARM] 275 Allow the default userspace alignment fault handler 276 behaviour to be specified. Bit 0 enables warnings, 277 bit 1 enables fixups, and bit 2 sends a segfault. 278 279 align_va_addr= [X86-64] 280 Align virtual addresses by clearing slice [14:12] when 281 allocating a VMA at process creation time. This option 282 gives you up to 3% performance improvement on AMD F15h 283 machines (where it is enabled by default) for a 284 CPU-intensive style benchmark, and it can vary highly in 285 a microbenchmark depending on workload and compiler. 286 287 32: only for 32-bit processes 288 64: only for 64-bit processes 289 on: enable for both 32- and 64-bit processes 290 off: disable for both 32- and 64-bit processes 291 292 alloc_snapshot [FTRACE] 293 Allocate the ftrace snapshot buffer on boot up when the 294 main buffer is allocated. This is handy if debugging 295 and you need to use tracing_snapshot() on boot up, and 296 do not want to use tracing_snapshot_alloc() as it needs 297 to be done where GFP_KERNEL allocations are allowed. 298 299 allow_mismatched_32bit_el0 [ARM64] 300 Allow execve() of 32-bit applications and setting of the 301 PER_LINUX32 personality on systems where only a strict 302 subset of the CPUs support 32-bit EL0. When this 303 parameter is present, the set of CPUs supporting 32-bit 304 EL0 is indicated by /sys/devices/system/cpu/aarch32_el0 305 and hot-unplug operations may be restricted. 306 307 See Documentation/arm64/asymmetric-32bit.rst for more 308 information. 309 310 amd_iommu= [HW,X86-64] 311 Pass parameters to the AMD IOMMU driver in the system. 312 Possible values are: 313 fullflush - Deprecated, equivalent to iommu.strict=1 314 off - do not initialize any AMD IOMMU found in 315 the system 316 force_isolation - Force device isolation for all 317 devices. The IOMMU driver is not 318 allowed anymore to lift isolation 319 requirements as needed. This option 320 does not override iommu=pt 321 force_enable - Force enable the IOMMU on platforms known 322 to be buggy with IOMMU enabled. Use this 323 option with care. 324 pgtbl_v1 - Use v1 page table for DMA-API (Default). 325 pgtbl_v2 - Use v2 page table for DMA-API. 326 327 amd_iommu_dump= [HW,X86-64] 328 Enable AMD IOMMU driver option to dump the ACPI table 329 for AMD IOMMU. With this option enabled, AMD IOMMU 330 driver will print ACPI tables for AMD IOMMU during 331 IOMMU initialization. 332 333 amd_iommu_intr= [HW,X86-64] 334 Specifies one of the following AMD IOMMU interrupt 335 remapping modes: 336 legacy - Use legacy interrupt remapping mode. 337 vapic - Use virtual APIC mode, which allows IOMMU 338 to inject interrupts directly into guest. 339 This mode requires kvm-amd.avic=1. 340 (Default when IOMMU HW support is present.) 341 342 amd_pstate= [X86] 343 disable 344 Do not enable amd_pstate as the default 345 scaling driver for the supported processors 346 passive 347 Use amd_pstate with passive mode as a scaling driver. 348 In this mode autonomous selection is disabled. 349 Driver requests a desired performance level and platform 350 tries to match the same performance level if it is 351 satisfied by guaranteed performance level. 352 active 353 Use amd_pstate_epp driver instance as the scaling driver, 354 driver provides a hint to the hardware if software wants 355 to bias toward performance (0x0) or energy efficiency (0xff) 356 to the CPPC firmware. then CPPC power algorithm will 357 calculate the runtime workload and adjust the realtime cores 358 frequency. 359 guided 360 Activate guided autonomous mode. Driver requests minimum and 361 maximum performance level and the platform autonomously 362 selects a performance level in this range and appropriate 363 to the current workload. 364 365 amijoy.map= [HW,JOY] Amiga joystick support 366 Map of devices attached to JOY0DAT and JOY1DAT 367 Format: <a>,<b> 368 See also Documentation/input/joydev/joystick.rst 369 370 analog.map= [HW,JOY] Analog joystick and gamepad support 371 Specifies type or capabilities of an analog joystick 372 connected to one of 16 gameports 373 Format: <type1>,<type2>,..<type16> 374 375 apc= [HW,SPARC] 376 Power management functions (SPARCstation-4/5 + deriv.) 377 Format: noidle 378 Disable APC CPU standby support. SPARCstation-Fox does 379 not play well with APC CPU idle - disable it if you have 380 APC and your system crashes randomly. 381 382 apic= [APIC,X86] Advanced Programmable Interrupt Controller 383 Change the output verbosity while booting 384 Format: { quiet (default) | verbose | debug } 385 Change the amount of debugging information output 386 when initialising the APIC and IO-APIC components. 387 For X86-32, this can also be used to specify an APIC 388 driver name. 389 Format: apic=driver_name 390 Examples: apic=bigsmp 391 392 apic_extnmi= [APIC,X86] External NMI delivery setting 393 Format: { bsp (default) | all | none } 394 bsp: External NMI is delivered only to CPU 0 395 all: External NMIs are broadcast to all CPUs as a 396 backup of CPU 0 397 none: External NMI is masked for all CPUs. This is 398 useful so that a dump capture kernel won't be 399 shot down by NMI 400 401 autoconf= [IPV6] 402 See Documentation/networking/ipv6.rst. 403 404 apm= [APM] Advanced Power Management 405 See header of arch/x86/kernel/apm_32.c. 406 407 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 408 Format: { "0" | "1" } 409 See security/apparmor/Kconfig help text 410 0 -- disable. 411 1 -- enable. 412 Default value is set via kernel config option. 413 414 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards 415 Format: <io>,<irq>,<nodeID> 416 417 arm64.nobti [ARM64] Unconditionally disable Branch Target 418 Identification support 419 420 arm64.nopauth [ARM64] Unconditionally disable Pointer Authentication 421 support 422 423 arm64.nomte [ARM64] Unconditionally disable Memory Tagging Extension 424 support 425 426 arm64.nosve [ARM64] Unconditionally disable Scalable Vector 427 Extension support 428 429 arm64.nosme [ARM64] Unconditionally disable Scalable Matrix 430 Extension support 431 432 ataflop= [HW,M68k] 433 434 atarimouse= [HW,MOUSE] Atari Mouse 435 436 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 437 EzKey and similar keyboards 438 439 atkbd.reset= [HW] Reset keyboard during initialization 440 441 atkbd.set= [HW] Select keyboard code set 442 Format: <int> (2 = AT (default), 3 = PS/2) 443 444 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 445 keyboards 446 447 atkbd.softraw= [HW] Choose between synthetic and real raw mode 448 Format: <bool> (0 = real, 1 = synthetic (default)) 449 450 atkbd.softrepeat= [HW] 451 Use software keyboard repeat 452 453 audit= [KNL] Enable the audit sub-system 454 Format: { "0" | "1" | "off" | "on" } 455 0 | off - kernel audit is disabled and can not be 456 enabled until the next reboot 457 unset - kernel audit is initialized but disabled and 458 will be fully enabled by the userspace auditd. 459 1 | on - kernel audit is initialized and partially 460 enabled, storing at most audit_backlog_limit 461 messages in RAM until it is fully enabled by the 462 userspace auditd. 463 Default: unset 464 465 audit_backlog_limit= [KNL] Set the audit queue size limit. 466 Format: <int> (must be >=0) 467 Default: 64 468 469 bau= [X86_UV] Enable the BAU on SGI UV. The default 470 behavior is to disable the BAU (i.e. bau=0). 471 Format: { "0" | "1" } 472 0 - Disable the BAU. 473 1 - Enable the BAU. 474 unset - Disable the BAU. 475 476 baycom_epp= [HW,AX25] 477 Format: <io>,<mode> 478 479 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem 480 Format: <io>,<mode> 481 See header of drivers/net/hamradio/baycom_par.c. 482 483 baycom_ser_fdx= [HW,AX25] 484 BayCom Serial Port AX.25 Modem (Full Duplex Mode) 485 Format: <io>,<irq>,<mode>[,<baud>] 486 See header of drivers/net/hamradio/baycom_ser_fdx.c. 487 488 baycom_ser_hdx= [HW,AX25] 489 BayCom Serial Port AX.25 Modem (Half Duplex Mode) 490 Format: <io>,<irq>,<mode> 491 See header of drivers/net/hamradio/baycom_ser_hdx.c. 492 493 bert_disable [ACPI] 494 Disable BERT OS support on buggy BIOSes. 495 496 bgrt_disable [ACPI][X86] 497 Disable BGRT to avoid flickering OEM logo. 498 499 blkdevparts= Manual partition parsing of block device(s) for 500 embedded devices based on command line input. 501 See Documentation/block/cmdline-partition.rst 502 503 boot_delay= Milliseconds to delay each printk during boot. 504 Only works if CONFIG_BOOT_PRINTK_DELAY is enabled, 505 and you may also have to specify "lpj=". Boot_delay 506 values larger than 10 seconds (10000) are assumed 507 erroneous and ignored. 508 Format: integer 509 510 bootconfig [KNL] 511 Extended command line options can be added to an initrd 512 and this will cause the kernel to look for it. 513 514 See Documentation/admin-guide/bootconfig.rst 515 516 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 517 bttv.radio= Most important insmod options are available as 518 kernel args too. 519 bttv.pll= See Documentation/admin-guide/media/bttv.rst 520 bttv.tuner= 521 522 bulk_remove=off [PPC] This parameter disables the use of the pSeries 523 firmware feature for flushing multiple hpte entries 524 at a time. 525 526 c101= [NET] Moxa C101 synchronous serial card 527 528 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 529 Sometimes CPU hardware bugs make them report the cache 530 size incorrectly. The kernel will attempt work arounds 531 to fix known problems, but for some CPUs it is not 532 possible to determine what the correct size should be. 533 This option provides an override for these situations. 534 535 carrier_timeout= 536 [NET] Specifies amount of time (in seconds) that 537 the kernel should wait for a network carrier. By default 538 it waits 120 seconds. 539 540 ca_keys= [KEYS] This parameter identifies a specific key(s) on 541 the system trusted keyring to be used for certificate 542 trust validation. 543 format: { id:<keyid> | builtin } 544 545 cca= [MIPS] Override the kernel pages' cache coherency 546 algorithm. Accepted values range from 0 to 7 547 inclusive. See arch/mips/include/asm/pgtable-bits.h 548 for platform specific values (SB1, Loongson3 and 549 others). 550 551 ccw_timeout_log [S390] 552 See Documentation/s390/common_io.rst for details. 553 554 cgroup_disable= [KNL] Disable a particular controller or optional feature 555 Format: {name of the controller(s) or feature(s) to disable} 556 The effects of cgroup_disable=foo are: 557 - foo isn't auto-mounted if you mount all cgroups in 558 a single hierarchy 559 - foo isn't visible as an individually mountable 560 subsystem 561 - if foo is an optional feature then the feature is 562 disabled and corresponding cgroup files are not 563 created 564 {Currently only "memory" controller deal with this and 565 cut the overhead, others just disable the usage. So 566 only cgroup_disable=memory is actually worthy} 567 Specifying "pressure" disables per-cgroup pressure 568 stall information accounting feature 569 570 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1 571 Format: { { controller | "all" | "named" } 572 [,{ controller | "all" | "named" }...] } 573 Like cgroup_disable, but only applies to cgroup v1; 574 the blacklisted controllers remain available in cgroup2. 575 "all" blacklists all controllers and "named" disables 576 named mounts. Specifying both "all" and "named" disables 577 all v1 hierarchies. 578 579 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 580 Format: <string> 581 nosocket -- Disable socket memory accounting. 582 nokmem -- Disable kernel memory accounting. 583 nobpf -- Disable BPF memory accounting. 584 585 checkreqprot= [SELINUX] Set initial checkreqprot flag value. 586 Format: { "0" | "1" } 587 See security/selinux/Kconfig help text. 588 0 -- check protection applied by kernel (includes 589 any implied execute protection). 590 1 -- check protection requested by application. 591 Default value is set via a kernel config option. 592 Value can be changed at runtime via 593 /sys/fs/selinux/checkreqprot. 594 Setting checkreqprot to 1 is deprecated. 595 596 cio_ignore= [S390] 597 See Documentation/s390/common_io.rst for details. 598 599 clearcpuid=X[,X...] [X86] 600 Disable CPUID feature X for the kernel. See 601 arch/x86/include/asm/cpufeatures.h for the valid bit 602 numbers X. Note the Linux-specific bits are not necessarily 603 stable over kernel options, but the vendor-specific 604 ones should be. 605 X can also be a string as appearing in the flags: line 606 in /proc/cpuinfo which does not have the above 607 instability issue. However, not all features have names 608 in /proc/cpuinfo. 609 Note that using this option will taint your kernel. 610 Also note that user programs calling CPUID directly 611 or using the feature without checking anything 612 will still see it. This just prevents it from 613 being used by the kernel or shown in /proc/cpuinfo. 614 Also note the kernel might malfunction if you disable 615 some critical bits. 616 617 clk_ignore_unused 618 [CLK] 619 Prevents the clock framework from automatically gating 620 clocks that have not been explicitly enabled by a Linux 621 device driver but are enabled in hardware at reset or 622 by the bootloader/firmware. Note that this does not 623 force such clocks to be always-on nor does it reserve 624 those clocks in any way. This parameter is useful for 625 debug and development, but should not be needed on a 626 platform with proper driver support. For more 627 information, see Documentation/driver-api/clk.rst. 628 629 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 630 [Deprecated] 631 Forces specified clocksource (if available) to be used 632 when calculating gettimeofday(). If specified 633 clocksource is not available, it defaults to PIT. 634 Format: { pit | tsc | cyclone | pmtmr } 635 636 clocksource= Override the default clocksource 637 Format: <string> 638 Override the default clocksource and use the clocksource 639 with the name specified. 640 Some clocksource names to choose from, depending on 641 the platform: 642 [all] jiffies (this is the base, fallback clocksource) 643 [ACPI] acpi_pm 644 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 645 pxa_timer,timer3,32k_counter,timer0_1 646 [X86-32] pit,hpet,tsc; 647 scx200_hrt on Geode; cyclone on IBM x440 648 [MIPS] MIPS 649 [PARISC] cr16 650 [S390] tod 651 [SH] SuperH 652 [SPARC64] tick 653 [X86-64] hpet,tsc 654 655 clocksource.arm_arch_timer.evtstrm= 656 [ARM,ARM64] 657 Format: <bool> 658 Enable/disable the eventstream feature of the ARM 659 architected timer so that code using WFE-based polling 660 loops can be debugged more effectively on production 661 systems. 662 663 clocksource.max_cswd_read_retries= [KNL] 664 Number of clocksource_watchdog() retries due to 665 external delays before the clock will be marked 666 unstable. Defaults to two retries, that is, 667 three attempts to read the clock under test. 668 669 clocksource.verify_n_cpus= [KNL] 670 Limit the number of CPUs checked for clocksources 671 marked with CLOCK_SOURCE_VERIFY_PERCPU that 672 are marked unstable due to excessive skew. 673 A negative value says to check all CPUs, while 674 zero says not to check any. Values larger than 675 nr_cpu_ids are silently truncated to nr_cpu_ids. 676 The actual CPUs are chosen randomly, with 677 no replacement if the same CPU is chosen twice. 678 679 clocksource-wdtest.holdoff= [KNL] 680 Set the time in seconds that the clocksource 681 watchdog test waits before commencing its tests. 682 Defaults to zero when built as a module and to 683 10 seconds when built into the kernel. 684 685 cma=nn[MG]@[start[MG][-end[MG]]] 686 [KNL,CMA] 687 Sets the size of kernel global memory area for 688 contiguous memory allocations and optionally the 689 placement constraint by the physical address range of 690 memory allocations. A value of 0 disables CMA 691 altogether. For more information, see 692 kernel/dma/contiguous.c 693 694 cma_pernuma=nn[MG] 695 [ARM64,KNL,CMA] 696 Sets the size of kernel per-numa memory area for 697 contiguous memory allocations. A value of 0 disables 698 per-numa CMA altogether. And If this option is not 699 specified, the default value is 0. 700 With per-numa CMA enabled, DMA users on node nid will 701 first try to allocate buffer from the pernuma area 702 which is located in node nid, if the allocation fails, 703 they will fallback to the global default memory area. 704 705 cmo_free_hint= [PPC] Format: { yes | no } 706 Specify whether pages are marked as being inactive 707 when they are freed. This is used in CMO environments 708 to determine OS memory pressure for page stealing by 709 a hypervisor. 710 Default: yes 711 712 coherent_pool=nn[KMG] [ARM,KNL] 713 Sets the size of memory pool for coherent, atomic dma 714 allocations, by default set to 256K. 715 716 com20020= [HW,NET] ARCnet - COM20020 chipset 717 Format: 718 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 719 720 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 721 Format: <io>[,<irq>] 722 723 com90xx= [HW,NET] 724 ARCnet - COM90xx chipset (memory-mapped buffers) 725 Format: <io>[,<irq>[,<memstart>]] 726 727 condev= [HW,S390] console device 728 conmode= 729 730 con3215_drop= [S390] 3215 console drop mode. 731 Format: y|n|Y|N|1|0 732 When set to true, drop data on the 3215 console when 733 the console buffer is full. In this case the 734 operator using a 3270 terminal emulator (for example 735 x3270) does not have to enter the clear key for the 736 console output to advance and the kernel to continue. 737 This leads to a much faster boot time when a 3270 738 terminal emulator is active. If no 3270 terminal 739 emulator is used, this parameter has no effect. 740 741 console= [KNL] Output console device and options. 742 743 tty<n> Use the virtual console device <n>. 744 745 ttyS<n>[,options] 746 ttyUSB0[,options] 747 Use the specified serial port. The options are of 748 the form "bbbbpnf", where "bbbb" is the baud rate, 749 "p" is parity ("n", "o", or "e"), "n" is number of 750 bits, and "f" is flow control ("r" for RTS or 751 omit it). Default is "9600n8". 752 753 See Documentation/admin-guide/serial-console.rst for more 754 information. See 755 Documentation/networking/netconsole.rst for an 756 alternative. 757 758 uart[8250],io,<addr>[,options] 759 uart[8250],mmio,<addr>[,options] 760 uart[8250],mmio16,<addr>[,options] 761 uart[8250],mmio32,<addr>[,options] 762 uart[8250],0x<addr>[,options] 763 Start an early, polled-mode console on the 8250/16550 764 UART at the specified I/O port or MMIO address, 765 switching to the matching ttyS device later. 766 MMIO inter-register address stride is either 8-bit 767 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 768 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 769 to be equivalent to 'mmio'. 'options' are specified in 770 the same format described for ttyS above; if unspecified, 771 the h/w is not re-initialized. 772 773 hvc<n> Use the hypervisor console device <n>. This is for 774 both Xen and PowerPC hypervisors. 775 776 { null | "" } 777 Use to disable console output, i.e., to have kernel 778 console messages discarded. 779 This must be the only console= parameter used on the 780 kernel command line. 781 782 If the device connected to the port is not a TTY but a braille 783 device, prepend "brl," before the device type, for instance 784 console=brl,ttyS0 785 For now, only VisioBraille is supported. 786 787 console_msg_format= 788 [KNL] Change console messages format 789 default 790 By default we print messages on consoles in 791 "[time stamp] text\n" format (time stamp may not be 792 printed, depending on CONFIG_PRINTK_TIME or 793 `printk_time' param). 794 syslog 795 Switch to syslog format: "<%u>[time stamp] text\n" 796 IOW, each message will have a facility and loglevel 797 prefix. The format is similar to one used by syslog() 798 syscall, or to executing "dmesg -S --raw" or to reading 799 from /proc/kmsg. 800 801 consoleblank= [KNL] The console blank (screen saver) timeout in 802 seconds. A value of 0 disables the blank timer. 803 Defaults to 0. 804 805 coredump_filter= 806 [KNL] Change the default value for 807 /proc/<pid>/coredump_filter. 808 See also Documentation/filesystems/proc.rst. 809 810 coresight_cpu_debug.enable 811 [ARM,ARM64] 812 Format: <bool> 813 Enable/disable the CPU sampling based debugging. 814 0: default value, disable debugging 815 1: enable debugging at boot time 816 817 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 818 Format: 819 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 820 821 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 822 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 823 Some features depend on CPU0. Known dependencies are: 824 1. Resume from suspend/hibernate depends on CPU0. 825 Suspend/hibernate will fail if CPU0 is offline and you 826 need to online CPU0 before suspend/hibernate. 827 2. PIC interrupts also depend on CPU0. CPU0 can't be 828 removed if a PIC interrupt is detected. 829 It's said poweroff/reboot may depend on CPU0 on some 830 machines although I haven't seen such issues so far 831 after CPU0 is offline on a few tested machines. 832 If the dependencies are under your control, you can 833 turn on cpu0_hotplug. 834 835 cpuidle.off=1 [CPU_IDLE] 836 disable the cpuidle sub-system 837 838 cpuidle.governor= 839 [CPU_IDLE] Name of the cpuidle governor to use. 840 841 cpufreq.off=1 [CPU_FREQ] 842 disable the cpufreq sub-system 843 844 cpufreq.default_governor= 845 [CPU_FREQ] Name of the default cpufreq governor or 846 policy to use. This governor must be registered in the 847 kernel before the cpufreq driver probes. 848 849 cpu_init_udelay=N 850 [X86] Delay for N microsec between assert and de-assert 851 of APIC INIT to start processors. This delay occurs 852 on every CPU online, such as boot, and resume from suspend. 853 Default: 10000 854 855 crash_kexec_post_notifiers 856 Run kdump after running panic-notifiers and dumping 857 kmsg. This only for the users who doubt kdump always 858 succeeds in any situation. 859 Note that this also increases risks of kdump failure, 860 because some panic notifiers can make the crashed 861 kernel more unstable. 862 863 crashkernel=size[KMG][@offset[KMG]] 864 [KNL] Using kexec, Linux can switch to a 'crash kernel' 865 upon panic. This parameter reserves the physical 866 memory region [offset, offset + size] for that kernel 867 image. If '@offset' is omitted, then a suitable offset 868 is selected automatically. 869 [KNL, X86-64, ARM64] Select a region under 4G first, and 870 fall back to reserve region above 4G when '@offset' 871 hasn't been specified. 872 See Documentation/admin-guide/kdump/kdump.rst for further details. 873 874 crashkernel=range1:size1[,range2:size2,...][@offset] 875 [KNL] Same as above, but depends on the memory 876 in the running system. The syntax of range is 877 start-[end] where start and end are both 878 a memory unit (amount[KMG]). See also 879 Documentation/admin-guide/kdump/kdump.rst for an example. 880 881 crashkernel=size[KMG],high 882 [KNL, X86-64, ARM64] range could be above 4G. Allow kernel 883 to allocate physical memory region from top, so could 884 be above 4G if system have more than 4G ram installed. 885 Otherwise memory region will be allocated below 4G, if 886 available. 887 It will be ignored if crashkernel=X is specified. 888 crashkernel=size[KMG],low 889 [KNL, X86-64, ARM64] range under 4G. When crashkernel=X,high 890 is passed, kernel could allocate physical memory region 891 above 4G, that cause second kernel crash on system 892 that require some amount of low memory, e.g. swiotlb 893 requires at least 64M+32K low memory, also enough extra 894 low memory is needed to make sure DMA buffers for 32-bit 895 devices won't run out. Kernel would try to allocate 896 default size of memory below 4G automatically. The default 897 size is platform dependent. 898 --> x86: max(swiotlb_size_or_default() + 8MiB, 256MiB) 899 --> arm64: 128MiB 900 This one lets the user specify own low range under 4G 901 for second kernel instead. 902 0: to disable low allocation. 903 It will be ignored when crashkernel=X,high is not used 904 or memory reserved is below 4G. 905 906 cryptomgr.notests 907 [KNL] Disable crypto self-tests 908 909 cs89x0_dma= [HW,NET] 910 Format: <dma> 911 912 cs89x0_media= [HW,NET] 913 Format: { rj45 | aui | bnc } 914 915 csdlock_debug= [KNL] Enable or disable debug add-ons of cross-CPU 916 function call handling. When switched on, 917 additional debug data is printed to the console 918 in case a hanging CPU is detected, and that 919 CPU is pinged again in order to try to resolve 920 the hang situation. The default value of this 921 option depends on the CSD_LOCK_WAIT_DEBUG_DEFAULT 922 Kconfig option. 923 924 dasd= [HW,NET] 925 See header of drivers/s390/block/dasd_devmap.c. 926 927 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 928 (one device per port) 929 Format: <port#>,<type> 930 See also Documentation/input/devices/joystick-parport.rst 931 932 debug [KNL] Enable kernel debugging (events log level). 933 934 debug_boot_weak_hash 935 [KNL] Enable printing [hashed] pointers early in the 936 boot sequence. If enabled, we use a weak hash instead 937 of siphash to hash pointers. Use this option if you are 938 seeing instances of '(___ptrval___)') and need to see a 939 value (hashed pointer) instead. Cryptographically 940 insecure, please do not use on production kernels. 941 942 debug_locks_verbose= 943 [KNL] verbose locking self-tests 944 Format: <int> 945 Print debugging info while doing the locking API 946 self-tests. 947 Bitmask for the various LOCKTYPE_ tests. Defaults to 0 948 (no extra messages), setting it to -1 (all bits set) 949 will print _a_lot_ more information - normally only 950 useful to lockdep developers. 951 952 debug_objects [KNL] Enable object debugging 953 954 debug_guardpage_minorder= 955 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 956 parameter allows control of the order of pages that will 957 be intentionally kept free (and hence protected) by the 958 buddy allocator. Bigger value increase the probability 959 of catching random memory corruption, but reduce the 960 amount of memory for normal system use. The maximum 961 possible value is MAX_ORDER/2. Setting this parameter 962 to 1 or 2 should be enough to identify most random 963 memory corruption problems caused by bugs in kernel or 964 driver code when a CPU writes to (or reads from) a 965 random memory location. Note that there exists a class 966 of memory corruptions problems caused by buggy H/W or 967 F/W or by drivers badly programming DMA (basically when 968 memory is written at bus level and the CPU MMU is 969 bypassed) which are not detectable by 970 CONFIG_DEBUG_PAGEALLOC, hence this option will not help 971 tracking down these problems. 972 973 debug_pagealloc= 974 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter 975 enables the feature at boot time. By default, it is 976 disabled and the system will work mostly the same as a 977 kernel built without CONFIG_DEBUG_PAGEALLOC. 978 Note: to get most of debug_pagealloc error reports, it's 979 useful to also enable the page_owner functionality. 980 on: enable the feature 981 982 debugfs= [KNL] This parameter enables what is exposed to userspace 983 and debugfs internal clients. 984 Format: { on, no-mount, off } 985 on: All functions are enabled. 986 no-mount: 987 Filesystem is not registered but kernel clients can 988 access APIs and a crashkernel can be used to read 989 its content. There is nothing to mount. 990 off: Filesystem is not registered and clients 991 get a -EPERM as result when trying to register files 992 or directories within debugfs. 993 This is equivalent of the runtime functionality if 994 debugfs was not enabled in the kernel at all. 995 Default value is set in build-time with a kernel configuration. 996 997 debugpat [X86] Enable PAT debugging 998 999 default_hugepagesz= 1000 [HW] The size of the default HugeTLB page. This is 1001 the size represented by the legacy /proc/ hugepages 1002 APIs. In addition, this is the default hugetlb size 1003 used for shmget(), mmap() and mounting hugetlbfs 1004 filesystems. If not specified, defaults to the 1005 architecture's default huge page size. Huge page 1006 sizes are architecture dependent. See also 1007 Documentation/admin-guide/mm/hugetlbpage.rst. 1008 Format: size[KMG] 1009 1010 deferred_probe_timeout= 1011 [KNL] Debugging option to set a timeout in seconds for 1012 deferred probe to give up waiting on dependencies to 1013 probe. Only specific dependencies (subsystems or 1014 drivers) that have opted in will be ignored. A timeout 1015 of 0 will timeout at the end of initcalls. If the time 1016 out hasn't expired, it'll be restarted by each 1017 successful driver registration. This option will also 1018 dump out devices still on the deferred probe list after 1019 retrying. 1020 1021 delayacct [KNL] Enable per-task delay accounting 1022 1023 dell_smm_hwmon.ignore_dmi= 1024 [HW] Continue probing hardware even if DMI data 1025 indicates that the driver is running on unsupported 1026 hardware. 1027 1028 dell_smm_hwmon.force= 1029 [HW] Activate driver even if SMM BIOS signature does 1030 not match list of supported models and enable otherwise 1031 blacklisted features. 1032 1033 dell_smm_hwmon.power_status= 1034 [HW] Report power status in /proc/i8k 1035 (disabled by default). 1036 1037 dell_smm_hwmon.restricted= 1038 [HW] Allow controlling fans only if SYS_ADMIN 1039 capability is set. 1040 1041 dell_smm_hwmon.fan_mult= 1042 [HW] Factor to multiply fan speed with. 1043 1044 dell_smm_hwmon.fan_max= 1045 [HW] Maximum configurable fan speed. 1046 1047 dfltcc= [HW,S390] 1048 Format: { on | off | def_only | inf_only | always } 1049 on: s390 zlib hardware support for compression on 1050 level 1 and decompression (default) 1051 off: No s390 zlib hardware support 1052 def_only: s390 zlib hardware support for deflate 1053 only (compression on level 1) 1054 inf_only: s390 zlib hardware support for inflate 1055 only (decompression) 1056 always: Same as 'on' but ignores the selected compression 1057 level always using hardware support (used for debugging) 1058 1059 dhash_entries= [KNL] 1060 Set number of hash buckets for dentry cache. 1061 1062 disable_1tb_segments [PPC] 1063 Disables the use of 1TB hash page table segments. This 1064 causes the kernel to fall back to 256MB segments which 1065 can be useful when debugging issues that require an SLB 1066 miss to occur. 1067 1068 disable= [IPV6] 1069 See Documentation/networking/ipv6.rst. 1070 1071 disable_radix [PPC] 1072 Disable RADIX MMU mode on POWER9 1073 1074 disable_tlbie [PPC] 1075 Disable TLBIE instruction. Currently does not work 1076 with KVM, with HASH MMU, or with coherent accelerators. 1077 1078 disable_cpu_apicid= [X86,APIC,SMP] 1079 Format: <int> 1080 The number of initial APIC ID for the 1081 corresponding CPU to be disabled at boot, 1082 mostly used for the kdump 2nd kernel to 1083 disable BSP to wake up multiple CPUs without 1084 causing system reset or hang due to sending 1085 INIT from AP to BSP. 1086 1087 disable_ddw [PPC/PSERIES] 1088 Disable Dynamic DMA Window support. Use this 1089 to workaround buggy firmware. 1090 1091 disable_ipv6= [IPV6] 1092 See Documentation/networking/ipv6.rst. 1093 1094 disable_mtrr_cleanup [X86] 1095 The kernel tries to adjust MTRR layout from continuous 1096 to discrete, to make X server driver able to add WB 1097 entry later. This parameter disables that. 1098 1099 disable_mtrr_trim [X86, Intel and AMD only] 1100 By default the kernel will trim any uncacheable 1101 memory out of your available memory pool based on 1102 MTRR settings. This parameter disables that behavior, 1103 possibly causing your machine to run very slowly. 1104 1105 disable_timer_pin_1 [X86] 1106 Disable PIN 1 of APIC timer 1107 Can be useful to work around chipset bugs. 1108 1109 dis_ucode_ldr [X86] Disable the microcode loader. 1110 1111 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 1112 this option disables the debugging code at boot. 1113 1114 dma_debug_entries=<number> 1115 This option allows to tune the number of preallocated 1116 entries for DMA-API debugging code. One entry is 1117 required per DMA-API allocation. Use this if the 1118 DMA-API debugging code disables itself because the 1119 architectural default is too low. 1120 1121 dma_debug_driver=<driver_name> 1122 With this option the DMA-API debugging driver 1123 filter feature can be enabled at boot time. Just 1124 pass the driver to filter for as the parameter. 1125 The filter can be disabled or changed to another 1126 driver later using sysfs. 1127 1128 driver_async_probe= [KNL] 1129 List of driver names to be probed asynchronously. * 1130 matches with all driver names. If * is specified, the 1131 rest of the listed driver names are those that will NOT 1132 match the *. 1133 Format: <driver_name1>,<driver_name2>... 1134 1135 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 1136 Broken monitors, graphic adapters, KVMs and EDIDless 1137 panels may send no or incorrect EDID data sets. 1138 This parameter allows to specify an EDID data sets 1139 in the /lib/firmware directory that are used instead. 1140 Generic built-in EDID data sets are used, if one of 1141 edid/1024x768.bin, edid/1280x1024.bin, 1142 edid/1680x1050.bin, or edid/1920x1080.bin is given 1143 and no file with the same name exists. Details and 1144 instructions how to build your own EDID data are 1145 available in Documentation/admin-guide/edid.rst. An EDID 1146 data set will only be used for a particular connector, 1147 if its name and a colon are prepended to the EDID 1148 name. Each connector may use a unique EDID data 1149 set by separating the files with a comma. An EDID 1150 data set with no connector name will be used for 1151 any connectors not explicitly specified. 1152 1153 dscc4.setup= [NET] 1154 1155 dt_cpu_ftrs= [PPC] 1156 Format: {"off" | "known"} 1157 Control how the dt_cpu_ftrs device-tree binding is 1158 used for CPU feature discovery and setup (if it 1159 exists). 1160 off: Do not use it, fall back to legacy cpu table. 1161 known: Do not pass through unknown features to guests 1162 or userspace, only those that the kernel is aware of. 1163 1164 dump_apple_properties [X86] 1165 Dump name and content of EFI device properties on 1166 x86 Macs. Useful for driver authors to determine 1167 what data is available or for reverse-engineering. 1168 1169 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 1170 <module>.dyndbg[="val"] 1171 Enable debug messages at boot time. See 1172 Documentation/admin-guide/dynamic-debug-howto.rst 1173 for details. 1174 1175 early_ioremap_debug [KNL] 1176 Enable debug messages in early_ioremap support. This 1177 is useful for tracking down temporary early mappings 1178 which are not unmapped. 1179 1180 earlycon= [KNL] Output early console device and options. 1181 1182 When used with no options, the early console is 1183 determined by stdout-path property in device tree's 1184 chosen node or the ACPI SPCR table if supported by 1185 the platform. 1186 1187 cdns,<addr>[,options] 1188 Start an early, polled-mode console on a Cadence 1189 (xuartps) serial port at the specified address. Only 1190 supported option is baud rate. If baud rate is not 1191 specified, the serial port must already be setup and 1192 configured. 1193 1194 uart[8250],io,<addr>[,options[,uartclk]] 1195 uart[8250],mmio,<addr>[,options[,uartclk]] 1196 uart[8250],mmio32,<addr>[,options[,uartclk]] 1197 uart[8250],mmio32be,<addr>[,options[,uartclk]] 1198 uart[8250],0x<addr>[,options] 1199 Start an early, polled-mode console on the 8250/16550 1200 UART at the specified I/O port or MMIO address. 1201 MMIO inter-register address stride is either 8-bit 1202 (mmio) or 32-bit (mmio32 or mmio32be). 1203 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1204 to be equivalent to 'mmio'. 'options' are specified 1205 in the same format described for "console=ttyS<n>"; if 1206 unspecified, the h/w is not initialized. 'uartclk' is 1207 the uart clock frequency; if unspecified, it is set 1208 to 'BASE_BAUD' * 16. 1209 1210 pl011,<addr> 1211 pl011,mmio32,<addr> 1212 Start an early, polled-mode console on a pl011 serial 1213 port at the specified address. The pl011 serial port 1214 must already be setup and configured. Options are not 1215 yet supported. If 'mmio32' is specified, then only 1216 the driver will use only 32-bit accessors to read/write 1217 the device registers. 1218 1219 liteuart,<addr> 1220 Start an early console on a litex serial port at the 1221 specified address. The serial port must already be 1222 setup and configured. Options are not yet supported. 1223 1224 meson,<addr> 1225 Start an early, polled-mode console on a meson serial 1226 port at the specified address. The serial port must 1227 already be setup and configured. Options are not yet 1228 supported. 1229 1230 msm_serial,<addr> 1231 Start an early, polled-mode console on an msm serial 1232 port at the specified address. The serial port 1233 must already be setup and configured. Options are not 1234 yet supported. 1235 1236 msm_serial_dm,<addr> 1237 Start an early, polled-mode console on an msm serial 1238 dm port at the specified address. The serial port 1239 must already be setup and configured. Options are not 1240 yet supported. 1241 1242 owl,<addr> 1243 Start an early, polled-mode console on a serial port 1244 of an Actions Semi SoC, such as S500 or S900, at the 1245 specified address. The serial port must already be 1246 setup and configured. Options are not yet supported. 1247 1248 rda,<addr> 1249 Start an early, polled-mode console on a serial port 1250 of an RDA Micro SoC, such as RDA8810PL, at the 1251 specified address. The serial port must already be 1252 setup and configured. Options are not yet supported. 1253 1254 sbi 1255 Use RISC-V SBI (Supervisor Binary Interface) for early 1256 console. 1257 1258 smh Use ARM semihosting calls for early console. 1259 1260 s3c2410,<addr> 1261 s3c2412,<addr> 1262 s3c2440,<addr> 1263 s3c6400,<addr> 1264 s5pv210,<addr> 1265 exynos4210,<addr> 1266 Use early console provided by serial driver available 1267 on Samsung SoCs, requires selecting proper type and 1268 a correct base address of the selected UART port. The 1269 serial port must already be setup and configured. 1270 Options are not yet supported. 1271 1272 lantiq,<addr> 1273 Start an early, polled-mode console on a lantiq serial 1274 (lqasc) port at the specified address. The serial port 1275 must already be setup and configured. Options are not 1276 yet supported. 1277 1278 lpuart,<addr> 1279 lpuart32,<addr> 1280 Use early console provided by Freescale LP UART driver 1281 found on Freescale Vybrid and QorIQ LS1021A processors. 1282 A valid base address must be provided, and the serial 1283 port must already be setup and configured. 1284 1285 ec_imx21,<addr> 1286 ec_imx6q,<addr> 1287 Start an early, polled-mode, output-only console on the 1288 Freescale i.MX UART at the specified address. The UART 1289 must already be setup and configured. 1290 1291 ar3700_uart,<addr> 1292 Start an early, polled-mode console on the 1293 Armada 3700 serial port at the specified 1294 address. The serial port must already be setup 1295 and configured. Options are not yet supported. 1296 1297 qcom_geni,<addr> 1298 Start an early, polled-mode console on a Qualcomm 1299 Generic Interface (GENI) based serial port at the 1300 specified address. The serial port must already be 1301 setup and configured. Options are not yet supported. 1302 1303 efifb,[options] 1304 Start an early, unaccelerated console on the EFI 1305 memory mapped framebuffer (if available). On cache 1306 coherent non-x86 systems that use system memory for 1307 the framebuffer, pass the 'ram' option so that it is 1308 mapped with the correct attributes. 1309 1310 linflex,<addr> 1311 Use early console provided by Freescale LINFlexD UART 1312 serial driver for NXP S32V234 SoCs. A valid base 1313 address must be provided, and the serial port must 1314 already be setup and configured. 1315 1316 earlyprintk= [X86,SH,ARM,M68k,S390] 1317 earlyprintk=vga 1318 earlyprintk=sclp 1319 earlyprintk=xen 1320 earlyprintk=serial[,ttySn[,baudrate]] 1321 earlyprintk=serial[,0x...[,baudrate]] 1322 earlyprintk=ttySn[,baudrate] 1323 earlyprintk=dbgp[debugController#] 1324 earlyprintk=pciserial[,force],bus:device.function[,baudrate] 1325 earlyprintk=xdbc[xhciController#] 1326 1327 earlyprintk is useful when the kernel crashes before 1328 the normal console is initialized. It is not enabled by 1329 default because it has some cosmetic problems. 1330 1331 Append ",keep" to not disable it when the real console 1332 takes over. 1333 1334 Only one of vga, serial, or usb debug port can 1335 be used at a time. 1336 1337 Currently only ttyS0 and ttyS1 may be specified by 1338 name. Other I/O ports may be explicitly specified 1339 on some architectures (x86 and arm at least) by 1340 replacing ttySn with an I/O port address, like this: 1341 earlyprintk=serial,0x1008,115200 1342 You can find the port for a given device in 1343 /proc/tty/driver/serial: 1344 2: uart:ST16650V2 port:00001008 irq:18 ... 1345 1346 Interaction with the standard serial driver is not 1347 very good. 1348 1349 The VGA output is eventually overwritten by 1350 the real console. 1351 1352 The xen option can only be used in Xen domains. 1353 1354 The sclp output can only be used on s390. 1355 1356 The optional "force" to "pciserial" enables use of a 1357 PCI device even when its classcode is not of the 1358 UART class. 1359 1360 edac_report= [HW,EDAC] Control how to report EDAC event 1361 Format: {"on" | "off" | "force"} 1362 on: enable EDAC to report H/W event. May be overridden 1363 by other higher priority error reporting module. 1364 off: disable H/W event reporting through EDAC. 1365 force: enforce the use of EDAC to report H/W event. 1366 default: on. 1367 1368 edd= [EDD] 1369 Format: {"off" | "on" | "skip[mbr]"} 1370 1371 efi= [EFI] 1372 Format: { "debug", "disable_early_pci_dma", 1373 "nochunk", "noruntime", "nosoftreserve", 1374 "novamap", "no_disable_early_pci_dma" } 1375 debug: enable misc debug output. 1376 disable_early_pci_dma: disable the busmaster bit on all 1377 PCI bridges while in the EFI boot stub. 1378 nochunk: disable reading files in "chunks" in the EFI 1379 boot stub, as chunking can cause problems with some 1380 firmware implementations. 1381 noruntime : disable EFI runtime services support 1382 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose) 1383 attribute may cause the kernel to reserve the 1384 memory range for a memory mapping driver to 1385 claim. Specify efi=nosoftreserve to disable this 1386 reservation and treat the memory by its base type 1387 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM"). 1388 novamap: do not call SetVirtualAddressMap(). 1389 no_disable_early_pci_dma: Leave the busmaster bit set 1390 on all PCI bridges while in the EFI boot stub 1391 1392 efi_no_storage_paranoia [EFI; X86] 1393 Using this parameter you can use more than 50% of 1394 your efi variable storage. Use this parameter only if 1395 you are really sure that your UEFI does sane gc and 1396 fulfills the spec otherwise your board may brick. 1397 1398 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] 1399 Add arbitrary attribute to specific memory range by 1400 updating original EFI memory map. 1401 Region of memory which aa attribute is added to is 1402 from ss to ss+nn. 1403 1404 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 1405 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) 1406 attribute is added to range 0x100000000-0x180000000 and 1407 0x10a0000000-0x1120000000. 1408 1409 If efi_fake_mem=8G@9G:0x40000 is specified, the 1410 EFI_MEMORY_SP(0x40000) attribute is added to 1411 range 0x240000000-0x43fffffff. 1412 1413 Using this parameter you can do debugging of EFI memmap 1414 related features. For example, you can do debugging of 1415 Address Range Mirroring feature even if your box 1416 doesn't support it, or mark specific memory as 1417 "soft reserved". 1418 1419 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1420 that is to be dynamically loaded by Linux. If there are 1421 multiple variables with the same name but with different 1422 vendor GUIDs, all of them will be loaded. See 1423 Documentation/admin-guide/acpi/ssdt-overlays.rst for details. 1424 1425 1426 eisa_irq_edge= [PARISC,HW] 1427 See header of drivers/parisc/eisa.c. 1428 1429 ekgdboc= [X86,KGDB] Allow early kernel console debugging 1430 Format: ekgdboc=kbd 1431 1432 This is designed to be used in conjunction with 1433 the boot argument: earlyprintk=vga 1434 1435 This parameter works in place of the kgdboc parameter 1436 but can only be used if the backing tty is available 1437 very early in the boot process. For early debugging 1438 via a serial port see kgdboc_earlycon instead. 1439 1440 elanfreq= [X86-32] 1441 See comment before function elanfreq_setup() in 1442 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1443 1444 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1445 Specifies physical address of start of kernel core 1446 image elf header and optionally the size. Generally 1447 kexec loader will pass this option to capture kernel. 1448 See Documentation/admin-guide/kdump/kdump.rst for details. 1449 1450 enable_mtrr_cleanup [X86] 1451 The kernel tries to adjust MTRR layout from continuous 1452 to discrete, to make X server driver able to add WB 1453 entry later. This parameter enables that. 1454 1455 enable_timer_pin_1 [X86] 1456 Enable PIN 1 of APIC timer 1457 Can be useful to work around chipset bugs 1458 (in particular on some ATI chipsets). 1459 The kernel tries to set a reasonable default. 1460 1461 enforcing= [SELINUX] Set initial enforcing status. 1462 Format: {"0" | "1"} 1463 See security/selinux/Kconfig help text. 1464 0 -- permissive (log only, no denials). 1465 1 -- enforcing (deny and log). 1466 Default value is 0. 1467 Value can be changed at runtime via 1468 /sys/fs/selinux/enforce. 1469 1470 erst_disable [ACPI] 1471 Disable Error Record Serialization Table (ERST) 1472 support. 1473 1474 ether= [HW,NET] Ethernet cards parameters 1475 This option is obsoleted by the "netdev=" option, which 1476 has equivalent usage. See its documentation for details. 1477 1478 evm= [EVM] 1479 Format: { "fix" } 1480 Permit 'security.evm' to be updated regardless of 1481 current integrity status. 1482 1483 early_page_ext [KNL] Enforces page_ext initialization to earlier 1484 stages so cover more early boot allocations. 1485 Please note that as side effect some optimizations 1486 might be disabled to achieve that (e.g. parallelized 1487 memory initialization is disabled) so the boot process 1488 might take longer, especially on systems with a lot of 1489 memory. Available with CONFIG_PAGE_EXTENSION=y. 1490 1491 failslab= 1492 fail_usercopy= 1493 fail_page_alloc= 1494 fail_make_request=[KNL] 1495 General fault injection mechanism. 1496 Format: <interval>,<probability>,<space>,<times> 1497 See also Documentation/fault-injection/. 1498 1499 fb_tunnels= [NET] 1500 Format: { initns | none } 1501 See Documentation/admin-guide/sysctl/net.rst for 1502 fb_tunnels_only_for_init_ns 1503 1504 floppy= [HW] 1505 See Documentation/admin-guide/blockdev/floppy.rst. 1506 1507 force_pal_cache_flush 1508 [IA-64] Avoid check_sal_cache_flush which may hang on 1509 buggy SAL_CACHE_FLUSH implementations. Using this 1510 parameter will force ia64_sal_cache_flush to call 1511 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1512 1513 forcepae [X86-32] 1514 Forcefully enable Physical Address Extension (PAE). 1515 Many Pentium M systems disable PAE but may have a 1516 functionally usable PAE implementation. 1517 Warning: use of this parameter will taint the kernel 1518 and may cause unknown problems. 1519 1520 ftrace=[tracer] 1521 [FTRACE] will set and start the specified tracer 1522 as early as possible in order to facilitate early 1523 boot debugging. 1524 1525 ftrace_boot_snapshot 1526 [FTRACE] On boot up, a snapshot will be taken of the 1527 ftrace ring buffer that can be read at: 1528 /sys/kernel/tracing/snapshot. 1529 This is useful if you need tracing information from kernel 1530 boot up that is likely to be overridden by user space 1531 start up functionality. 1532 1533 Optionally, the snapshot can also be defined for a tracing 1534 instance that was created by the trace_instance= command 1535 line parameter. 1536 1537 trace_instance=foo,sched_switch ftrace_boot_snapshot=foo 1538 1539 The above will cause the "foo" tracing instance to trigger 1540 a snapshot at the end of boot up. 1541 1542 ftrace_dump_on_oops[=orig_cpu] 1543 [FTRACE] will dump the trace buffers on oops. 1544 If no parameter is passed, ftrace will dump 1545 buffers of all CPUs, but if you pass orig_cpu, it will 1546 dump only the buffer of the CPU that triggered the 1547 oops. 1548 1549 ftrace_filter=[function-list] 1550 [FTRACE] Limit the functions traced by the function 1551 tracer at boot up. function-list is a comma-separated 1552 list of functions. This list can be changed at run 1553 time by the set_ftrace_filter file in the debugfs 1554 tracing directory. 1555 1556 ftrace_notrace=[function-list] 1557 [FTRACE] Do not trace the functions specified in 1558 function-list. This list can be changed at run time 1559 by the set_ftrace_notrace file in the debugfs 1560 tracing directory. 1561 1562 ftrace_graph_filter=[function-list] 1563 [FTRACE] Limit the top level callers functions traced 1564 by the function graph tracer at boot up. 1565 function-list is a comma-separated list of functions 1566 that can be changed at run time by the 1567 set_graph_function file in the debugfs tracing directory. 1568 1569 ftrace_graph_notrace=[function-list] 1570 [FTRACE] Do not trace from the functions specified in 1571 function-list. This list is a comma-separated list of 1572 functions that can be changed at run time by the 1573 set_graph_notrace file in the debugfs tracing directory. 1574 1575 ftrace_graph_max_depth=<uint> 1576 [FTRACE] Used with the function graph tracer. This is 1577 the max depth it will trace into a function. This value 1578 can be changed at run time by the max_graph_depth file 1579 in the tracefs tracing directory. default: 0 (no limit) 1580 1581 fw_devlink= [KNL] Create device links between consumer and supplier 1582 devices by scanning the firmware to infer the 1583 consumer/supplier relationships. This feature is 1584 especially useful when drivers are loaded as modules as 1585 it ensures proper ordering of tasks like device probing 1586 (suppliers first, then consumers), supplier boot state 1587 clean up (only after all consumers have probed), 1588 suspend/resume & runtime PM (consumers first, then 1589 suppliers). 1590 Format: { off | permissive | on | rpm } 1591 off -- Don't create device links from firmware info. 1592 permissive -- Create device links from firmware info 1593 but use it only for ordering boot state clean 1594 up (sync_state() calls). 1595 on -- Create device links from firmware info and use it 1596 to enforce probe and suspend/resume ordering. 1597 rpm -- Like "on", but also use to order runtime PM. 1598 1599 fw_devlink.strict=<bool> 1600 [KNL] Treat all inferred dependencies as mandatory 1601 dependencies. This only applies for fw_devlink=on|rpm. 1602 Format: <bool> 1603 1604 fw_devlink.sync_state = 1605 [KNL] When all devices that could probe have finished 1606 probing, this parameter controls what to do with 1607 devices that haven't yet received their sync_state() 1608 calls. 1609 Format: { strict | timeout } 1610 strict -- Default. Continue waiting on consumers to 1611 probe successfully. 1612 timeout -- Give up waiting on consumers and call 1613 sync_state() on any devices that haven't yet 1614 received their sync_state() calls after 1615 deferred_probe_timeout has expired or by 1616 late_initcall() if !CONFIG_MODULES. 1617 1618 gamecon.map[2|3]= 1619 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1620 support via parallel port (up to 5 devices per port) 1621 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1622 See also Documentation/input/devices/joystick-parport.rst 1623 1624 gamma= [HW,DRM] 1625 1626 gart_fix_e820= [X86-64] disable the fix e820 for K8 GART 1627 Format: off | on 1628 default: on 1629 1630 gcov_persist= [GCOV] When non-zero (default), profiling data for 1631 kernel modules is saved and remains accessible via 1632 debugfs, even when the module is unloaded/reloaded. 1633 When zero, profiling data is discarded and associated 1634 debugfs files are removed at module unload time. 1635 1636 goldfish [X86] Enable the goldfish android emulator platform. 1637 Don't use this when you are not running on the 1638 android emulator 1639 1640 gpio-mockup.gpio_mockup_ranges 1641 [HW] Sets the ranges of gpiochip of for this device. 1642 Format: <start1>,<end1>,<start2>,<end2>... 1643 gpio-mockup.gpio_mockup_named_lines 1644 [HW] Let the driver know GPIO lines should be named. 1645 1646 gpt [EFI] Forces disk with valid GPT signature but 1647 invalid Protective MBR to be treated as GPT. If the 1648 primary GPT is corrupted, it enables the backup/alternate 1649 GPT to be used instead. 1650 1651 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1652 the "Enable 0" bit of the configuration register. 1653 Format: 0 | 1 1654 Default: 0 1655 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1656 the "Enable 0" bit of the configuration register. 1657 Format: 0 | 1 1658 Default: 0 1659 grcan.select= [HW] Select which physical interface to use. 1660 Format: 0 | 1 1661 Default: 0 1662 grcan.txsize= [HW] Sets the size of the tx buffer. 1663 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1664 Default: 1024 1665 grcan.rxsize= [HW] Sets the size of the rx buffer. 1666 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1667 Default: 1024 1668 1669 hardened_usercopy= 1670 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 1671 hardening is enabled for this boot. Hardened 1672 usercopy checking is used to protect the kernel 1673 from reading or writing beyond known memory 1674 allocation boundaries as a proactive defense 1675 against bounds-checking flaws in the kernel's 1676 copy_to_user()/copy_from_user() interface. 1677 on Perform hardened usercopy checks (default). 1678 off Disable hardened usercopy checks. 1679 1680 hardlockup_all_cpu_backtrace= 1681 [KNL] Should the hard-lockup detector generate 1682 backtraces on all cpus. 1683 Format: 0 | 1 1684 1685 hashdist= [KNL,NUMA] Large hashes allocated during boot 1686 are distributed across NUMA nodes. Defaults on 1687 for 64-bit NUMA, off otherwise. 1688 Format: 0 | 1 (for off | on) 1689 1690 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1691 1692 hd= [EIDE] (E)IDE hard drive subsystem geometry 1693 Format: <cyl>,<head>,<sect> 1694 1695 hest_disable [ACPI] 1696 Disable Hardware Error Source Table (HEST) support; 1697 corresponding firmware-first mode error processing 1698 logic will be disabled. 1699 1700 hibernate= [HIBERNATION] 1701 noresume Don't check if there's a hibernation image 1702 present during boot. 1703 nocompress Don't compress/decompress hibernation images. 1704 no Disable hibernation and resume. 1705 protect_image Turn on image protection during restoration 1706 (that will set all pages holding image data 1707 during restoration read-only). 1708 1709 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1710 size of <nn>. This works even on boxes that have no 1711 highmem otherwise. This also works to reduce highmem 1712 size on bigger boxes. 1713 1714 highres= [KNL] Enable/disable high resolution timer mode. 1715 Valid parameters: "on", "off" 1716 Default: "on" 1717 1718 hlt [BUGS=ARM,SH] 1719 1720 hostname= [KNL] Set the hostname (aka UTS nodename). 1721 Format: <string> 1722 This allows setting the system's hostname during early 1723 startup. This sets the name returned by gethostname. 1724 Using this parameter to set the hostname makes it 1725 possible to ensure the hostname is correctly set before 1726 any userspace processes run, avoiding the possibility 1727 that a process may call gethostname before the hostname 1728 has been explicitly set, resulting in the calling 1729 process getting an incorrect result. The string must 1730 not exceed the maximum allowed hostname length (usually 1731 64 characters) and will be truncated otherwise. 1732 1733 hpet= [X86-32,HPET] option to control HPET usage 1734 Format: { enable (default) | disable | force | 1735 verbose } 1736 disable: disable HPET and use PIT instead 1737 force: allow force enabled of undocumented chips (ICH4, 1738 VIA, nVidia) 1739 verbose: show contents of HPET registers during setup 1740 1741 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1742 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1743 1744 hugepages= [HW] Number of HugeTLB pages to allocate at boot. 1745 If this follows hugepagesz (below), it specifies 1746 the number of pages of hugepagesz to be allocated. 1747 If this is the first HugeTLB parameter on the command 1748 line, it specifies the number of pages to allocate for 1749 the default huge page size. If using node format, the 1750 number of pages to allocate per-node can be specified. 1751 See also Documentation/admin-guide/mm/hugetlbpage.rst. 1752 Format: <integer> or (node format) 1753 <node>:<integer>[,<node>:<integer>] 1754 1755 hugepagesz= 1756 [HW] The size of the HugeTLB pages. This is used in 1757 conjunction with hugepages (above) to allocate huge 1758 pages of a specific size at boot. The pair 1759 hugepagesz=X hugepages=Y can be specified once for 1760 each supported huge page size. Huge page sizes are 1761 architecture dependent. See also 1762 Documentation/admin-guide/mm/hugetlbpage.rst. 1763 Format: size[KMG] 1764 1765 hugetlb_cma= [HW,CMA] The size of a CMA area used for allocation 1766 of gigantic hugepages. Or using node format, the size 1767 of a CMA area per node can be specified. 1768 Format: nn[KMGTPE] or (node format) 1769 <node>:nn[KMGTPE][,<node>:nn[KMGTPE]] 1770 1771 Reserve a CMA area of given size and allocate gigantic 1772 hugepages using the CMA allocator. If enabled, the 1773 boot-time allocation of gigantic hugepages is skipped. 1774 1775 hugetlb_free_vmemmap= 1776 [KNL] Requires CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP 1777 enabled. 1778 Control if HugeTLB Vmemmap Optimization (HVO) is enabled. 1779 Allows heavy hugetlb users to free up some more 1780 memory (7 * PAGE_SIZE for each 2MB hugetlb page). 1781 Format: { on | off (default) } 1782 1783 on: enable HVO 1784 off: disable HVO 1785 1786 Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y, 1787 the default is on. 1788 1789 Note that the vmemmap pages may be allocated from the added 1790 memory block itself when memory_hotplug.memmap_on_memory is 1791 enabled, those vmemmap pages cannot be optimized even if this 1792 feature is enabled. Other vmemmap pages not allocated from 1793 the added memory block itself do not be affected. 1794 1795 hung_task_panic= 1796 [KNL] Should the hung task detector generate panics. 1797 Format: 0 | 1 1798 1799 A value of 1 instructs the kernel to panic when a 1800 hung task is detected. The default value is controlled 1801 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time 1802 option. The value selected by this boot parameter can 1803 be changed later by the kernel.hung_task_panic sysctl. 1804 1805 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1806 terminal devices. Valid values: 0..8 1807 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1808 If specified, z/VM IUCV HVC accepts connections 1809 from listed z/VM user IDs only. 1810 1811 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations 1812 which allow the hypervisor to 'idle' the 1813 guest on lock contention. 1814 1815 i2c_bus= [HW] Override the default board specific I2C bus speed 1816 or register an additional I2C bus that is not 1817 registered from board initialization code. 1818 Format: 1819 <bus_id>,<clkrate> 1820 1821 i8042.debug [HW] Toggle i8042 debug mode 1822 i8042.unmask_kbd_data 1823 [HW] Enable printing of interrupt data from the KBD port 1824 (disabled by default, and as a pre-condition 1825 requires that i8042.debug=1 be enabled) 1826 i8042.direct [HW] Put keyboard port into non-translated mode 1827 i8042.dumbkbd [HW] Pretend that controller can only read data from 1828 keyboard and cannot control its state 1829 (Don't attempt to blink the leds) 1830 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1831 i8042.nokbd [HW] Don't check/create keyboard port 1832 i8042.noloop [HW] Disable the AUX Loopback command while probing 1833 for the AUX port 1834 i8042.nomux [HW] Don't check presence of an active multiplexing 1835 controller 1836 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1837 controllers 1838 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1839 i8042.reset [HW] Reset the controller during init, cleanup and 1840 suspend-to-ram transitions, only during s2r 1841 transitions, or never reset 1842 Format: { 1 | Y | y | 0 | N | n } 1843 1, Y, y: always reset controller 1844 0, N, n: don't ever reset controller 1845 Default: only on s2r transitions on x86; most other 1846 architectures force reset to be always executed 1847 i8042.unlock [HW] Unlock (ignore) the keylock 1848 i8042.kbdreset [HW] Reset device connected to KBD port 1849 i8042.probe_defer 1850 [HW] Allow deferred probing upon i8042 probe errors 1851 1852 i810= [HW,DRM] 1853 1854 i915.invert_brightness= 1855 [DRM] Invert the sense of the variable that is used to 1856 set the brightness of the panel backlight. Normally a 1857 brightness value of 0 indicates backlight switched off, 1858 and the maximum of the brightness value sets the backlight 1859 to maximum brightness. If this parameter is set to 0 1860 (default) and the machine requires it, or this parameter 1861 is set to 1, a brightness value of 0 sets the backlight 1862 to maximum brightness, and the maximum of the brightness 1863 value switches the backlight off. 1864 -1 -- never invert brightness 1865 0 -- machine default 1866 1 -- force brightness inversion 1867 1868 icn= [HW,ISDN] 1869 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1870 1871 1872 idle= [X86] 1873 Format: idle=poll, idle=halt, idle=nomwait 1874 Poll forces a polling idle loop that can slightly 1875 improve the performance of waking up a idle CPU, but 1876 will use a lot of power and make the system run hot. 1877 Not recommended. 1878 idle=halt: Halt is forced to be used for CPU idle. 1879 In such case C2/C3 won't be used again. 1880 idle=nomwait: Disable mwait for CPU C-states 1881 1882 idxd.sva= [HW] 1883 Format: <bool> 1884 Allow force disabling of Shared Virtual Memory (SVA) 1885 support for the idxd driver. By default it is set to 1886 true (1). 1887 1888 idxd.tc_override= [HW] 1889 Format: <bool> 1890 Allow override of default traffic class configuration 1891 for the device. By default it is set to false (0). 1892 1893 ieee754= [MIPS] Select IEEE Std 754 conformance mode 1894 Format: { strict | legacy | 2008 | relaxed } 1895 Default: strict 1896 1897 Choose which programs will be accepted for execution 1898 based on the IEEE 754 NaN encoding(s) supported by 1899 the FPU and the NaN encoding requested with the value 1900 of an ELF file header flag individually set by each 1901 binary. Hardware implementations are permitted to 1902 support either or both of the legacy and the 2008 NaN 1903 encoding mode. 1904 1905 Available settings are as follows: 1906 strict accept binaries that request a NaN encoding 1907 supported by the FPU 1908 legacy only accept legacy-NaN binaries, if supported 1909 by the FPU 1910 2008 only accept 2008-NaN binaries, if supported 1911 by the FPU 1912 relaxed accept any binaries regardless of whether 1913 supported by the FPU 1914 1915 The FPU emulator is always able to support both NaN 1916 encodings, so if no FPU hardware is present or it has 1917 been disabled with 'nofpu', then the settings of 1918 'legacy' and '2008' strap the emulator accordingly, 1919 'relaxed' straps the emulator for both legacy-NaN and 1920 2008-NaN, whereas 'strict' enables legacy-NaN only on 1921 legacy processors and both NaN encodings on MIPS32 or 1922 MIPS64 CPUs. 1923 1924 The setting for ABS.fmt/NEG.fmt instruction execution 1925 mode generally follows that for the NaN encoding, 1926 except where unsupported by hardware. 1927 1928 ignore_loglevel [KNL] 1929 Ignore loglevel setting - this will print /all/ 1930 kernel messages to the console. Useful for debugging. 1931 We also add it as printk module parameter, so users 1932 could change it dynamically, usually by 1933 /sys/module/printk/parameters/ignore_loglevel. 1934 1935 ignore_rlimit_data 1936 Ignore RLIMIT_DATA setting for data mappings, 1937 print warning at first misuse. Can be changed via 1938 /sys/module/kernel/parameters/ignore_rlimit_data. 1939 1940 ihash_entries= [KNL] 1941 Set number of hash buckets for inode cache. 1942 1943 ima_appraise= [IMA] appraise integrity measurements 1944 Format: { "off" | "enforce" | "fix" | "log" } 1945 default: "enforce" 1946 1947 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 1948 The builtin appraise policy appraises all files 1949 owned by uid=0. 1950 1951 ima_canonical_fmt [IMA] 1952 Use the canonical format for the binary runtime 1953 measurements, instead of host native format. 1954 1955 ima_hash= [IMA] 1956 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1957 | sha512 | ... } 1958 default: "sha1" 1959 1960 The list of supported hash algorithms is defined 1961 in crypto/hash_info.h. 1962 1963 ima_policy= [IMA] 1964 The builtin policies to load during IMA setup. 1965 Format: "tcb | appraise_tcb | secure_boot | 1966 fail_securely | critical_data" 1967 1968 The "tcb" policy measures all programs exec'd, files 1969 mmap'd for exec, and all files opened with the read 1970 mode bit set by either the effective uid (euid=0) or 1971 uid=0. 1972 1973 The "appraise_tcb" policy appraises the integrity of 1974 all files owned by root. 1975 1976 The "secure_boot" policy appraises the integrity 1977 of files (eg. kexec kernel image, kernel modules, 1978 firmware, policy, etc) based on file signatures. 1979 1980 The "fail_securely" policy forces file signature 1981 verification failure also on privileged mounted 1982 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 1983 flag. 1984 1985 The "critical_data" policy measures kernel integrity 1986 critical data. 1987 1988 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 1989 Load a policy which meets the needs of the Trusted 1990 Computing Base. This means IMA will measure all 1991 programs exec'd, files mmap'd for exec, and all files 1992 opened for read by uid=0. 1993 1994 ima_template= [IMA] 1995 Select one of defined IMA measurements template formats. 1996 Formats: { "ima" | "ima-ng" | "ima-ngv2" | "ima-sig" | 1997 "ima-sigv2" } 1998 Default: "ima-ng" 1999 2000 ima_template_fmt= 2001 [IMA] Define a custom template format. 2002 Format: { "field1|...|fieldN" } 2003 2004 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 2005 Format: <min_file_size> 2006 Set the minimal file size for using asynchronous hash. 2007 If left unspecified, ahash usage is disabled. 2008 2009 ahash performance varies for different data sizes on 2010 different crypto accelerators. This option can be used 2011 to achieve the best performance for a particular HW. 2012 2013 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 2014 Format: <bufsize> 2015 Set hashing buffer size. Default: 4k. 2016 2017 ahash performance varies for different chunk sizes on 2018 different crypto accelerators. This option can be used 2019 to achieve best performance for particular HW. 2020 2021 init= [KNL] 2022 Format: <full_path> 2023 Run specified binary instead of /sbin/init as init 2024 process. 2025 2026 initcall_debug [KNL] Trace initcalls as they are executed. Useful 2027 for working out where the kernel is dying during 2028 startup. 2029 2030 initcall_blacklist= [KNL] Do not execute a comma-separated list of 2031 initcall functions. Useful for debugging built-in 2032 modules and initcalls. 2033 2034 initramfs_async= [KNL] 2035 Format: <bool> 2036 Default: 1 2037 This parameter controls whether the initramfs 2038 image is unpacked asynchronously, concurrently 2039 with devices being probed and 2040 initialized. This should normally just work, 2041 but as a debugging aid, one can get the 2042 historical behaviour of the initramfs 2043 unpacking being completed before device_ and 2044 late_ initcalls. 2045 2046 initrd= [BOOT] Specify the location of the initial ramdisk 2047 2048 initrdmem= [KNL] Specify a physical address and size from which to 2049 load the initrd. If an initrd is compiled in or 2050 specified in the bootparams, it takes priority over this 2051 setting. 2052 Format: ss[KMG],nn[KMG] 2053 Default is 0, 0 2054 2055 init_on_alloc= [MM] Fill newly allocated pages and heap objects with 2056 zeroes. 2057 Format: 0 | 1 2058 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON. 2059 2060 init_on_free= [MM] Fill freed pages and heap objects with zeroes. 2061 Format: 0 | 1 2062 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON. 2063 2064 init_pkru= [X86] Specify the default memory protection keys rights 2065 register contents for all processes. 0x55555554 by 2066 default (disallow access to all but pkey 0). Can 2067 override in debugfs after boot. 2068 2069 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 2070 Format: <irq> 2071 2072 int_pln_enable [X86] Enable power limit notification interrupt 2073 2074 integrity_audit=[IMA] 2075 Format: { "0" | "1" } 2076 0 -- basic integrity auditing messages. (Default) 2077 1 -- additional integrity auditing messages. 2078 2079 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 2080 on 2081 Enable intel iommu driver. 2082 off 2083 Disable intel iommu driver. 2084 igfx_off [Default Off] 2085 By default, gfx is mapped as normal device. If a gfx 2086 device has a dedicated DMAR unit, the DMAR unit is 2087 bypassed by not enabling DMAR with this option. In 2088 this case, gfx device will use physical address for 2089 DMA. 2090 strict [Default Off] 2091 Deprecated, equivalent to iommu.strict=1. 2092 sp_off [Default Off] 2093 By default, super page will be supported if Intel IOMMU 2094 has the capability. With this option, super page will 2095 not be supported. 2096 sm_on 2097 Enable the Intel IOMMU scalable mode if the hardware 2098 advertises that it has support for the scalable mode 2099 translation. 2100 sm_off 2101 Disallow use of the Intel IOMMU scalable mode. 2102 tboot_noforce [Default Off] 2103 Do not force the Intel IOMMU enabled under tboot. 2104 By default, tboot will force Intel IOMMU on, which 2105 could harm performance of some high-throughput 2106 devices like 40GBit network cards, even if identity 2107 mapping is enabled. 2108 Note that using this option lowers the security 2109 provided by tboot because it makes the system 2110 vulnerable to DMA attacks. 2111 2112 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 2113 0 disables intel_idle and fall back on acpi_idle. 2114 1 to 9 specify maximum depth of C-state. 2115 2116 intel_pstate= [X86] 2117 disable 2118 Do not enable intel_pstate as the default 2119 scaling driver for the supported processors 2120 passive 2121 Use intel_pstate as a scaling driver, but configure it 2122 to work with generic cpufreq governors (instead of 2123 enabling its internal governor). This mode cannot be 2124 used along with the hardware-managed P-states (HWP) 2125 feature. 2126 force 2127 Enable intel_pstate on systems that prohibit it by default 2128 in favor of acpi-cpufreq. Forcing the intel_pstate driver 2129 instead of acpi-cpufreq may disable platform features, such 2130 as thermal controls and power capping, that rely on ACPI 2131 P-States information being indicated to OSPM and therefore 2132 should be used with caution. This option does not work with 2133 processors that aren't supported by the intel_pstate driver 2134 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 2135 no_hwp 2136 Do not enable hardware P state control (HWP) 2137 if available. 2138 hwp_only 2139 Only load intel_pstate on systems which support 2140 hardware P state control (HWP) if available. 2141 support_acpi_ppc 2142 Enforce ACPI _PPC performance limits. If the Fixed ACPI 2143 Description Table, specifies preferred power management 2144 profile as "Enterprise Server" or "Performance Server", 2145 then this feature is turned on by default. 2146 per_cpu_perf_limits 2147 Allow per-logical-CPU P-State performance control limits using 2148 cpufreq sysfs interface 2149 2150 intremap= [X86-64, Intel-IOMMU] 2151 on enable Interrupt Remapping (default) 2152 off disable Interrupt Remapping 2153 nosid disable Source ID checking 2154 no_x2apic_optout 2155 BIOS x2APIC opt-out request will be ignored 2156 nopost disable Interrupt Posting 2157 2158 iomem= Disable strict checking of access to MMIO memory 2159 strict regions from userspace. 2160 relaxed 2161 2162 iommu= [X86] 2163 off 2164 force 2165 noforce 2166 biomerge 2167 panic 2168 nopanic 2169 merge 2170 nomerge 2171 soft 2172 pt [X86] 2173 nopt [X86] 2174 nobypass [PPC/POWERNV] 2175 Disable IOMMU bypass, using IOMMU for PCI devices. 2176 2177 iommu.forcedac= [ARM64, X86] Control IOVA allocation for PCI devices. 2178 Format: { "0" | "1" } 2179 0 - Try to allocate a 32-bit DMA address first, before 2180 falling back to the full range if needed. 2181 1 - Allocate directly from the full usable range, 2182 forcing Dual Address Cycle for PCI cards supporting 2183 greater than 32-bit addressing. 2184 2185 iommu.strict= [ARM64, X86] Configure TLB invalidation behaviour 2186 Format: { "0" | "1" } 2187 0 - Lazy mode. 2188 Request that DMA unmap operations use deferred 2189 invalidation of hardware TLBs, for increased 2190 throughput at the cost of reduced device isolation. 2191 Will fall back to strict mode if not supported by 2192 the relevant IOMMU driver. 2193 1 - Strict mode. 2194 DMA unmap operations invalidate IOMMU hardware TLBs 2195 synchronously. 2196 unset - Use value of CONFIG_IOMMU_DEFAULT_DMA_{LAZY,STRICT}. 2197 Note: on x86, strict mode specified via one of the 2198 legacy driver-specific options takes precedence. 2199 2200 iommu.passthrough= 2201 [ARM64, X86] Configure DMA to bypass the IOMMU by default. 2202 Format: { "0" | "1" } 2203 0 - Use IOMMU translation for DMA. 2204 1 - Bypass the IOMMU for DMA. 2205 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 2206 2207 io7= [HW] IO7 for Marvel-based Alpha systems 2208 See comment before marvel_specify_io7 in 2209 arch/alpha/kernel/core_marvel.c. 2210 2211 io_delay= [X86] I/O delay method 2212 0x80 2213 Standard port 0x80 based delay 2214 0xed 2215 Alternate port 0xed based delay (needed on some systems) 2216 udelay 2217 Simple two microseconds delay 2218 none 2219 No delay 2220 2221 ip= [IP_PNP] 2222 See Documentation/admin-guide/nfs/nfsroot.rst. 2223 2224 ipcmni_extend [KNL] Extend the maximum number of unique System V 2225 IPC identifiers from 32,768 to 16,777,216. 2226 2227 irqaffinity= [SMP] Set the default irq affinity mask 2228 The argument is a cpu list, as described above. 2229 2230 irqchip.gicv2_force_probe= 2231 [ARM, ARM64] 2232 Format: <bool> 2233 Force the kernel to look for the second 4kB page 2234 of a GICv2 controller even if the memory range 2235 exposed by the device tree is too small. 2236 2237 irqchip.gicv3_nolpi= 2238 [ARM, ARM64] 2239 Force the kernel to ignore the availability of 2240 LPIs (and by consequence ITSs). Intended for system 2241 that use the kernel as a bootloader, and thus want 2242 to let secondary kernels in charge of setting up 2243 LPIs. 2244 2245 irqchip.gicv3_pseudo_nmi= [ARM64] 2246 Enables support for pseudo-NMIs in the kernel. This 2247 requires the kernel to be built with 2248 CONFIG_ARM64_PSEUDO_NMI. 2249 2250 irqfixup [HW] 2251 When an interrupt is not handled search all handlers 2252 for it. Intended to get systems with badly broken 2253 firmware running. 2254 2255 irqpoll [HW] 2256 When an interrupt is not handled search all handlers 2257 for it. Also check all handlers each timer 2258 interrupt. Intended to get systems with badly broken 2259 firmware running. 2260 2261 isapnp= [ISAPNP] 2262 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 2263 2264 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 2265 [Deprecated - use cpusets instead] 2266 Format: [flag-list,]<cpu-list> 2267 2268 Specify one or more CPUs to isolate from disturbances 2269 specified in the flag list (default: domain): 2270 2271 nohz 2272 Disable the tick when a single task runs. 2273 2274 A residual 1Hz tick is offloaded to workqueues, which you 2275 need to affine to housekeeping through the global 2276 workqueue's affinity configured via the 2277 /sys/devices/virtual/workqueue/cpumask sysfs file, or 2278 by using the 'domain' flag described below. 2279 2280 NOTE: by default the global workqueue runs on all CPUs, 2281 so to protect individual CPUs the 'cpumask' file has to 2282 be configured manually after bootup. 2283 2284 domain 2285 Isolate from the general SMP balancing and scheduling 2286 algorithms. Note that performing domain isolation this way 2287 is irreversible: it's not possible to bring back a CPU to 2288 the domains once isolated through isolcpus. It's strongly 2289 advised to use cpusets instead to disable scheduler load 2290 balancing through the "cpuset.sched_load_balance" file. 2291 It offers a much more flexible interface where CPUs can 2292 move in and out of an isolated set anytime. 2293 2294 You can move a process onto or off an "isolated" CPU via 2295 the CPU affinity syscalls or cpuset. 2296 <cpu number> begins at 0 and the maximum value is 2297 "number of CPUs in system - 1". 2298 2299 managed_irq 2300 2301 Isolate from being targeted by managed interrupts 2302 which have an interrupt mask containing isolated 2303 CPUs. The affinity of managed interrupts is 2304 handled by the kernel and cannot be changed via 2305 the /proc/irq/* interfaces. 2306 2307 This isolation is best effort and only effective 2308 if the automatically assigned interrupt mask of a 2309 device queue contains isolated and housekeeping 2310 CPUs. If housekeeping CPUs are online then such 2311 interrupts are directed to the housekeeping CPU 2312 so that IO submitted on the housekeeping CPU 2313 cannot disturb the isolated CPU. 2314 2315 If a queue's affinity mask contains only isolated 2316 CPUs then this parameter has no effect on the 2317 interrupt routing decision, though interrupts are 2318 only delivered when tasks running on those 2319 isolated CPUs submit IO. IO submitted on 2320 housekeeping CPUs has no influence on those 2321 queues. 2322 2323 The format of <cpu-list> is described above. 2324 2325 iucv= [HW,NET] 2326 2327 ivrs_ioapic [HW,X86-64] 2328 Provide an override to the IOAPIC-ID<->DEVICE-ID 2329 mapping provided in the IVRS ACPI table. 2330 By default, PCI segment is 0, and can be omitted. 2331 2332 For example, to map IOAPIC-ID decimal 10 to 2333 PCI segment 0x1 and PCI device 00:14.0, 2334 write the parameter as: 2335 ivrs_ioapic=10@0001:00:14.0 2336 2337 Deprecated formats: 2338 * To map IOAPIC-ID decimal 10 to PCI device 00:14.0 2339 write the parameter as: 2340 ivrs_ioapic[10]=00:14.0 2341 * To map IOAPIC-ID decimal 10 to PCI segment 0x1 and 2342 PCI device 00:14.0 write the parameter as: 2343 ivrs_ioapic[10]=0001:00:14.0 2344 2345 ivrs_hpet [HW,X86-64] 2346 Provide an override to the HPET-ID<->DEVICE-ID 2347 mapping provided in the IVRS ACPI table. 2348 By default, PCI segment is 0, and can be omitted. 2349 2350 For example, to map HPET-ID decimal 10 to 2351 PCI segment 0x1 and PCI device 00:14.0, 2352 write the parameter as: 2353 ivrs_hpet=10@0001:00:14.0 2354 2355 Deprecated formats: 2356 * To map HPET-ID decimal 0 to PCI device 00:14.0 2357 write the parameter as: 2358 ivrs_hpet[0]=00:14.0 2359 * To map HPET-ID decimal 10 to PCI segment 0x1 and 2360 PCI device 00:14.0 write the parameter as: 2361 ivrs_ioapic[10]=0001:00:14.0 2362 2363 ivrs_acpihid [HW,X86-64] 2364 Provide an override to the ACPI-HID:UID<->DEVICE-ID 2365 mapping provided in the IVRS ACPI table. 2366 By default, PCI segment is 0, and can be omitted. 2367 2368 For example, to map UART-HID:UID AMD0020:0 to 2369 PCI segment 0x1 and PCI device ID 00:14.5, 2370 write the parameter as: 2371 ivrs_acpihid=AMD0020:0@0001:00:14.5 2372 2373 Deprecated formats: 2374 * To map UART-HID:UID AMD0020:0 to PCI segment is 0, 2375 PCI device ID 00:14.5, write the parameter as: 2376 ivrs_acpihid[00:14.5]=AMD0020:0 2377 * To map UART-HID:UID AMD0020:0 to PCI segment 0x1 and 2378 PCI device ID 00:14.5, write the parameter as: 2379 ivrs_acpihid[0001:00:14.5]=AMD0020:0 2380 2381 js= [HW,JOY] Analog joystick 2382 See Documentation/input/joydev/joystick.rst. 2383 2384 kasan_multi_shot 2385 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 2386 report on every invalid memory access. Without this 2387 parameter KASAN will print report only for the first 2388 invalid access. 2389 2390 keep_bootcon [KNL] 2391 Do not unregister boot console at start. This is only 2392 useful for debugging when something happens in the window 2393 between unregistering the boot console and initializing 2394 the real console. 2395 2396 keepinitrd [HW,ARM] 2397 2398 kernelcore= [KNL,X86,IA-64,PPC] 2399 Format: nn[KMGTPE] | nn% | "mirror" 2400 This parameter specifies the amount of memory usable by 2401 the kernel for non-movable allocations. The requested 2402 amount is spread evenly throughout all nodes in the 2403 system as ZONE_NORMAL. The remaining memory is used for 2404 movable memory in its own zone, ZONE_MOVABLE. In the 2405 event, a node is too small to have both ZONE_NORMAL and 2406 ZONE_MOVABLE, kernelcore memory will take priority and 2407 other nodes will have a larger ZONE_MOVABLE. 2408 2409 ZONE_MOVABLE is used for the allocation of pages that 2410 may be reclaimed or moved by the page migration 2411 subsystem. Note that allocations like PTEs-from-HighMem 2412 still use the HighMem zone if it exists, and the Normal 2413 zone if it does not. 2414 2415 It is possible to specify the exact amount of memory in 2416 the form of "nn[KMGTPE]", a percentage of total system 2417 memory in the form of "nn%", or "mirror". If "mirror" 2418 option is specified, mirrored (reliable) memory is used 2419 for non-movable allocations and remaining memory is used 2420 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 2421 are exclusive, so you cannot specify multiple forms. 2422 2423 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 2424 Format: <Controller#>[,poll interval] 2425 The controller # is the number of the ehci usb debug 2426 port as it is probed via PCI. The poll interval is 2427 optional and is the number seconds in between 2428 each poll cycle to the debug port in case you need 2429 the functionality for interrupting the kernel with 2430 gdb or control-c on the dbgp connection. When 2431 not using this parameter you use sysrq-g to break into 2432 the kernel debugger. 2433 2434 kgdboc= [KGDB,HW] kgdb over consoles. 2435 Requires a tty driver that supports console polling, 2436 or a supported polling keyboard driver (non-usb). 2437 Serial only format: <serial_device>[,baud] 2438 keyboard only format: kbd 2439 keyboard and serial format: kbd,<serial_device>[,baud] 2440 Optional Kernel mode setting: 2441 kms, kbd format: kms,kbd 2442 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 2443 2444 kgdboc_earlycon= [KGDB,HW] 2445 If the boot console provides the ability to read 2446 characters and can work in polling mode, you can use 2447 this parameter to tell kgdb to use it as a backend 2448 until the normal console is registered. Intended to 2449 be used together with the kgdboc parameter which 2450 specifies the normal console to transition to. 2451 2452 The name of the early console should be specified 2453 as the value of this parameter. Note that the name of 2454 the early console might be different than the tty 2455 name passed to kgdboc. It's OK to leave the value 2456 blank and the first boot console that implements 2457 read() will be picked. 2458 2459 kgdbwait [KGDB] Stop kernel execution and enter the 2460 kernel debugger at the earliest opportunity. 2461 2462 kmac= [MIPS] Korina ethernet MAC address. 2463 Configure the RouterBoard 532 series on-chip 2464 Ethernet adapter MAC address. 2465 2466 kmemleak= [KNL] Boot-time kmemleak enable/disable 2467 Valid arguments: on, off 2468 Default: on 2469 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 2470 the default is off. 2471 2472 kprobe_event=[probe-list] 2473 [FTRACE] Add kprobe events and enable at boot time. 2474 The probe-list is a semicolon delimited list of probe 2475 definitions. Each definition is same as kprobe_events 2476 interface, but the parameters are comma delimited. 2477 For example, to add a kprobe event on vfs_read with 2478 arg1 and arg2, add to the command line; 2479 2480 kprobe_event=p,vfs_read,$arg1,$arg2 2481 2482 See also Documentation/trace/kprobetrace.rst "Kernel 2483 Boot Parameter" section. 2484 2485 kpti= [ARM64] Control page table isolation of user 2486 and kernel address spaces. 2487 Default: enabled on cores which need mitigation. 2488 0: force disabled 2489 1: force enabled 2490 2491 kunit.enable= [KUNIT] Enable executing KUnit tests. Requires 2492 CONFIG_KUNIT to be set to be fully enabled. The 2493 default value can be overridden via 2494 KUNIT_DEFAULT_ENABLED. 2495 Default is 1 (enabled) 2496 2497 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 2498 Default is 0 (don't ignore, but inject #GP) 2499 2500 kvm.eager_page_split= 2501 [KVM,X86] Controls whether or not KVM will try to 2502 proactively split all huge pages during dirty logging. 2503 Eager page splitting reduces interruptions to vCPU 2504 execution by eliminating the write-protection faults 2505 and MMU lock contention that would otherwise be 2506 required to split huge pages lazily. 2507 2508 VM workloads that rarely perform writes or that write 2509 only to a small region of VM memory may benefit from 2510 disabling eager page splitting to allow huge pages to 2511 still be used for reads. 2512 2513 The behavior of eager page splitting depends on whether 2514 KVM_DIRTY_LOG_INITIALLY_SET is enabled or disabled. If 2515 disabled, all huge pages in a memslot will be eagerly 2516 split when dirty logging is enabled on that memslot. If 2517 enabled, eager page splitting will be performed during 2518 the KVM_CLEAR_DIRTY ioctl, and only for the pages being 2519 cleared. 2520 2521 Eager page splitting is only supported when kvm.tdp_mmu=Y. 2522 2523 Default is Y (on). 2524 2525 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 2526 Default is false (don't support). 2527 2528 kvm.nx_huge_pages= 2529 [KVM] Controls the software workaround for the 2530 X86_BUG_ITLB_MULTIHIT bug. 2531 force : Always deploy workaround. 2532 off : Never deploy workaround. 2533 auto : Deploy workaround based on the presence of 2534 X86_BUG_ITLB_MULTIHIT. 2535 2536 Default is 'auto'. 2537 2538 If the software workaround is enabled for the host, 2539 guests do need not to enable it for nested guests. 2540 2541 kvm.nx_huge_pages_recovery_ratio= 2542 [KVM] Controls how many 4KiB pages are periodically zapped 2543 back to huge pages. 0 disables the recovery, otherwise if 2544 the value is N KVM will zap 1/Nth of the 4KiB pages every 2545 period (see below). The default is 60. 2546 2547 kvm.nx_huge_pages_recovery_period_ms= 2548 [KVM] Controls the time period at which KVM zaps 4KiB pages 2549 back to huge pages. If the value is a non-zero N, KVM will 2550 zap a portion (see ratio above) of the pages every N msecs. 2551 If the value is 0 (the default), KVM will pick a period based 2552 on the ratio, such that a page is zapped after 1 hour on average. 2553 2554 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 2555 Default is 1 (enabled) 2556 2557 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 2558 for all guests. 2559 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 2560 2561 kvm-arm.mode= 2562 [KVM,ARM] Select one of KVM/arm64's modes of operation. 2563 2564 none: Forcefully disable KVM. 2565 2566 nvhe: Standard nVHE-based mode, without support for 2567 protected guests. 2568 2569 protected: nVHE-based mode with support for guests whose 2570 state is kept private from the host. 2571 2572 nested: VHE-based mode with support for nested 2573 virtualization. Requires at least ARMv8.3 2574 hardware. 2575 2576 Defaults to VHE/nVHE based on hardware support. Setting 2577 mode to "protected" will disable kexec and hibernation 2578 for the host. "nested" is experimental and should be 2579 used with extreme caution. 2580 2581 kvm-arm.vgic_v3_group0_trap= 2582 [KVM,ARM] Trap guest accesses to GICv3 group-0 2583 system registers 2584 2585 kvm-arm.vgic_v3_group1_trap= 2586 [KVM,ARM] Trap guest accesses to GICv3 group-1 2587 system registers 2588 2589 kvm-arm.vgic_v3_common_trap= 2590 [KVM,ARM] Trap guest accesses to GICv3 common 2591 system registers 2592 2593 kvm-arm.vgic_v4_enable= 2594 [KVM,ARM] Allow use of GICv4 for direct injection of 2595 LPIs. 2596 2597 kvm_cma_resv_ratio=n [PPC] 2598 Reserves given percentage from system memory area for 2599 contiguous memory allocation for KVM hash pagetable 2600 allocation. 2601 By default it reserves 5% of total system memory. 2602 Format: <integer> 2603 Default: 5 2604 2605 kvm-intel.ept= [KVM,Intel] Disable extended page tables 2606 (virtualized MMU) support on capable Intel chips. 2607 Default is 1 (enabled) 2608 2609 kvm-intel.emulate_invalid_guest_state= 2610 [KVM,Intel] Disable emulation of invalid guest state. 2611 Ignored if kvm-intel.enable_unrestricted_guest=1, as 2612 guest state is never invalid for unrestricted guests. 2613 This param doesn't apply to nested guests (L2), as KVM 2614 never emulates invalid L2 guest state. 2615 Default is 1 (enabled) 2616 2617 kvm-intel.flexpriority= 2618 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 2619 Default is 1 (enabled) 2620 2621 kvm-intel.nested= 2622 [KVM,Intel] Enable VMX nesting (nVMX). 2623 Default is 0 (disabled) 2624 2625 kvm-intel.unrestricted_guest= 2626 [KVM,Intel] Disable unrestricted guest feature 2627 (virtualized real and unpaged mode) on capable 2628 Intel chips. Default is 1 (enabled) 2629 2630 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 2631 CVE-2018-3620. 2632 2633 Valid arguments: never, cond, always 2634 2635 always: L1D cache flush on every VMENTER. 2636 cond: Flush L1D on VMENTER only when the code between 2637 VMEXIT and VMENTER can leak host memory. 2638 never: Disables the mitigation 2639 2640 Default is cond (do L1 cache flush in specific instances) 2641 2642 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 2643 feature (tagged TLBs) on capable Intel chips. 2644 Default is 1 (enabled) 2645 2646 l1d_flush= [X86,INTEL] 2647 Control mitigation for L1D based snooping vulnerability. 2648 2649 Certain CPUs are vulnerable to an exploit against CPU 2650 internal buffers which can forward information to a 2651 disclosure gadget under certain conditions. 2652 2653 In vulnerable processors, the speculatively 2654 forwarded data can be used in a cache side channel 2655 attack, to access data to which the attacker does 2656 not have direct access. 2657 2658 This parameter controls the mitigation. The 2659 options are: 2660 2661 on - enable the interface for the mitigation 2662 2663 l1tf= [X86] Control mitigation of the L1TF vulnerability on 2664 affected CPUs 2665 2666 The kernel PTE inversion protection is unconditionally 2667 enabled and cannot be disabled. 2668 2669 full 2670 Provides all available mitigations for the 2671 L1TF vulnerability. Disables SMT and 2672 enables all mitigations in the 2673 hypervisors, i.e. unconditional L1D flush. 2674 2675 SMT control and L1D flush control via the 2676 sysfs interface is still possible after 2677 boot. Hypervisors will issue a warning 2678 when the first VM is started in a 2679 potentially insecure configuration, 2680 i.e. SMT enabled or L1D flush disabled. 2681 2682 full,force 2683 Same as 'full', but disables SMT and L1D 2684 flush runtime control. Implies the 2685 'nosmt=force' command line option. 2686 (i.e. sysfs control of SMT is disabled.) 2687 2688 flush 2689 Leaves SMT enabled and enables the default 2690 hypervisor mitigation, i.e. conditional 2691 L1D flush. 2692 2693 SMT control and L1D flush control via the 2694 sysfs interface is still possible after 2695 boot. Hypervisors will issue a warning 2696 when the first VM is started in a 2697 potentially insecure configuration, 2698 i.e. SMT enabled or L1D flush disabled. 2699 2700 flush,nosmt 2701 2702 Disables SMT and enables the default 2703 hypervisor mitigation. 2704 2705 SMT control and L1D flush control via the 2706 sysfs interface is still possible after 2707 boot. Hypervisors will issue a warning 2708 when the first VM is started in a 2709 potentially insecure configuration, 2710 i.e. SMT enabled or L1D flush disabled. 2711 2712 flush,nowarn 2713 Same as 'flush', but hypervisors will not 2714 warn when a VM is started in a potentially 2715 insecure configuration. 2716 2717 off 2718 Disables hypervisor mitigations and doesn't 2719 emit any warnings. 2720 It also drops the swap size and available 2721 RAM limit restriction on both hypervisor and 2722 bare metal. 2723 2724 Default is 'flush'. 2725 2726 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 2727 2728 l2cr= [PPC] 2729 2730 l3cr= [PPC] 2731 2732 lapic [X86-32,APIC] Enable the local APIC even if BIOS 2733 disabled it. 2734 2735 lapic= [X86,APIC] Do not use TSC deadline 2736 value for LAPIC timer one-shot implementation. Default 2737 back to the programmable timer unit in the LAPIC. 2738 Format: notscdeadline 2739 2740 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 2741 in C2 power state. 2742 2743 libata.dma= [LIBATA] DMA control 2744 libata.dma=0 Disable all PATA and SATA DMA 2745 libata.dma=1 PATA and SATA Disk DMA only 2746 libata.dma=2 ATAPI (CDROM) DMA only 2747 libata.dma=4 Compact Flash DMA only 2748 Combinations also work, so libata.dma=3 enables DMA 2749 for disks and CDROMs, but not CFs. 2750 2751 libata.ignore_hpa= [LIBATA] Ignore HPA limit 2752 libata.ignore_hpa=0 keep BIOS limits (default) 2753 libata.ignore_hpa=1 ignore limits, using full disk 2754 2755 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 2756 when set. 2757 Format: <int> 2758 2759 libata.force= [LIBATA] Force configurations. The format is a comma- 2760 separated list of "[ID:]VAL" where ID is PORT[.DEVICE]. 2761 PORT and DEVICE are decimal numbers matching port, link 2762 or device. Basically, it matches the ATA ID string 2763 printed on console by libata. If the whole ID part is 2764 omitted, the last PORT and DEVICE values are used. If 2765 ID hasn't been specified yet, the configuration applies 2766 to all ports, links and devices. 2767 2768 If only DEVICE is omitted, the parameter applies to 2769 the port and all links and devices behind it. DEVICE 2770 number of 0 either selects the first device or the 2771 first fan-out link behind PMP device. It does not 2772 select the host link. DEVICE number of 15 selects the 2773 host link and device attached to it. 2774 2775 The VAL specifies the configuration to force. As long 2776 as there is no ambiguity, shortcut notation is allowed. 2777 For example, both 1.5 and 1.5G would work for 1.5Gbps. 2778 The following configurations can be forced. 2779 2780 * Cable type: 40c, 80c, short40c, unk, ign or sata. 2781 Any ID with matching PORT is used. 2782 2783 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 2784 2785 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 2786 udma[/][16,25,33,44,66,100,133] notation is also 2787 allowed. 2788 2789 * nohrst, nosrst, norst: suppress hard, soft and both 2790 resets. 2791 2792 * rstonce: only attempt one reset during hot-unplug 2793 link recovery. 2794 2795 * [no]dbdelay: Enable or disable the extra 200ms delay 2796 before debouncing a link PHY and device presence 2797 detection. 2798 2799 * [no]ncq: Turn on or off NCQ. 2800 2801 * [no]ncqtrim: Enable or disable queued DSM TRIM. 2802 2803 * [no]ncqati: Enable or disable NCQ trim on ATI chipset. 2804 2805 * [no]trim: Enable or disable (unqueued) TRIM. 2806 2807 * trim_zero: Indicate that TRIM command zeroes data. 2808 2809 * max_trim_128m: Set 128M maximum trim size limit. 2810 2811 * [no]dma: Turn on or off DMA transfers. 2812 2813 * atapi_dmadir: Enable ATAPI DMADIR bridge support. 2814 2815 * atapi_mod16_dma: Enable the use of ATAPI DMA for 2816 commands that are not a multiple of 16 bytes. 2817 2818 * [no]dmalog: Enable or disable the use of the 2819 READ LOG DMA EXT command to access logs. 2820 2821 * [no]iddevlog: Enable or disable access to the 2822 identify device data log. 2823 2824 * [no]logdir: Enable or disable access to the general 2825 purpose log directory. 2826 2827 * max_sec_128: Set transfer size limit to 128 sectors. 2828 2829 * max_sec_1024: Set or clear transfer size limit to 2830 1024 sectors. 2831 2832 * max_sec_lba48: Set or clear transfer size limit to 2833 65535 sectors. 2834 2835 * [no]lpm: Enable or disable link power management. 2836 2837 * [no]setxfer: Indicate if transfer speed mode setting 2838 should be skipped. 2839 2840 * [no]fua: Disable or enable FUA (Force Unit Access) 2841 support for devices supporting this feature. 2842 2843 * dump_id: Dump IDENTIFY data. 2844 2845 * disable: Disable this device. 2846 2847 If there are multiple matching configurations changing 2848 the same attribute, the last one is used. 2849 2850 load_ramdisk= [RAM] [Deprecated] 2851 2852 lockd.nlm_grace_period=P [NFS] Assign grace period. 2853 Format: <integer> 2854 2855 lockd.nlm_tcpport=N [NFS] Assign TCP port. 2856 Format: <integer> 2857 2858 lockd.nlm_timeout=T [NFS] Assign timeout value. 2859 Format: <integer> 2860 2861 lockd.nlm_udpport=M [NFS] Assign UDP port. 2862 Format: <integer> 2863 2864 lockdown= [SECURITY] 2865 { integrity | confidentiality } 2866 Enable the kernel lockdown feature. If set to 2867 integrity, kernel features that allow userland to 2868 modify the running kernel are disabled. If set to 2869 confidentiality, kernel features that allow userland 2870 to extract confidential information from the kernel 2871 are also disabled. 2872 2873 locktorture.nreaders_stress= [KNL] 2874 Set the number of locking read-acquisition kthreads. 2875 Defaults to being automatically set based on the 2876 number of online CPUs. 2877 2878 locktorture.nwriters_stress= [KNL] 2879 Set the number of locking write-acquisition kthreads. 2880 2881 locktorture.onoff_holdoff= [KNL] 2882 Set time (s) after boot for CPU-hotplug testing. 2883 2884 locktorture.onoff_interval= [KNL] 2885 Set time (s) between CPU-hotplug operations, or 2886 zero to disable CPU-hotplug testing. 2887 2888 locktorture.shuffle_interval= [KNL] 2889 Set task-shuffle interval (jiffies). Shuffling 2890 tasks allows some CPUs to go into dyntick-idle 2891 mode during the locktorture test. 2892 2893 locktorture.shutdown_secs= [KNL] 2894 Set time (s) after boot system shutdown. This 2895 is useful for hands-off automated testing. 2896 2897 locktorture.stat_interval= [KNL] 2898 Time (s) between statistics printk()s. 2899 2900 locktorture.stutter= [KNL] 2901 Time (s) to stutter testing, for example, 2902 specifying five seconds causes the test to run for 2903 five seconds, wait for five seconds, and so on. 2904 This tests the locking primitive's ability to 2905 transition abruptly to and from idle. 2906 2907 locktorture.torture_type= [KNL] 2908 Specify the locking implementation to test. 2909 2910 locktorture.verbose= [KNL] 2911 Enable additional printk() statements. 2912 2913 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 2914 Format: <irq> 2915 2916 loglevel= All Kernel Messages with a loglevel smaller than the 2917 console loglevel will be printed to the console. It can 2918 also be changed with klogd or other programs. The 2919 loglevels are defined as follows: 2920 2921 0 (KERN_EMERG) system is unusable 2922 1 (KERN_ALERT) action must be taken immediately 2923 2 (KERN_CRIT) critical conditions 2924 3 (KERN_ERR) error conditions 2925 4 (KERN_WARNING) warning conditions 2926 5 (KERN_NOTICE) normal but significant condition 2927 6 (KERN_INFO) informational 2928 7 (KERN_DEBUG) debug-level messages 2929 2930 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 2931 in bytes. n must be a power of two and greater 2932 than the minimal size. The minimal size is defined 2933 by LOG_BUF_SHIFT kernel config parameter. There is 2934 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2935 that allows to increase the default size depending on 2936 the number of CPUs. See init/Kconfig for more details. 2937 2938 logo.nologo [FB] Disables display of the built-in Linux logo. 2939 This may be used to provide more screen space for 2940 kernel log messages and is useful when debugging 2941 kernel boot problems. 2942 2943 lp=0 [LP] Specify parallel ports to use, e.g, 2944 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 2945 lp=reset first parallel port). 'lp=0' disables the 2946 lp=auto printer driver. 'lp=reset' (which can be 2947 specified in addition to the ports) causes 2948 attached printers to be reset. Using 2949 lp=port1,port2,... specifies the parallel ports 2950 to associate lp devices with, starting with 2951 lp0. A port specification may be 'none' to skip 2952 that lp device, or a parport name such as 2953 'parport0'. Specifying 'lp=auto' instead of a 2954 port specification list means that device IDs 2955 from each port should be examined, to see if 2956 an IEEE 1284-compliant printer is attached; if 2957 so, the driver will manage that printer. 2958 See also header of drivers/char/lp.c. 2959 2960 lpj=n [KNL] 2961 Sets loops_per_jiffy to given constant, thus avoiding 2962 time-consuming boot-time autodetection (up to 250 ms per 2963 CPU). 0 enables autodetection (default). To determine 2964 the correct value for your kernel, boot with normal 2965 autodetection and see what value is printed. Note that 2966 on SMP systems the preset will be applied to all CPUs, 2967 which is likely to cause problems if your CPUs need 2968 significantly divergent settings. An incorrect value 2969 will cause delays in the kernel to be wrong, leading to 2970 unpredictable I/O errors and other breakage. Although 2971 unlikely, in the extreme case this might damage your 2972 hardware. 2973 2974 ltpc= [NET] 2975 Format: <io>,<irq>,<dma> 2976 2977 lsm.debug [SECURITY] Enable LSM initialization debugging output. 2978 2979 lsm=lsm1,...,lsmN 2980 [SECURITY] Choose order of LSM initialization. This 2981 overrides CONFIG_LSM, and the "security=" parameter. 2982 2983 machvec= [IA-64] Force the use of a particular machine-vector 2984 (machvec) in a generic kernel. 2985 Example: machvec=hpzx1 2986 2987 machtype= [Loongson] Share the same kernel image file between 2988 different yeeloong laptops. 2989 Example: machtype=lemote-yeeloong-2f-7inch 2990 2991 max_addr=nn[KMG] [KNL,BOOT,IA-64] All physical memory greater 2992 than or equal to this physical address is ignored. 2993 2994 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2995 will bring up during bootup. maxcpus=n : n >= 0 limits 2996 the kernel to bring up 'n' processors. Surely after 2997 bootup you can bring up the other plugged cpu by executing 2998 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 2999 only takes effect during system bootup. 3000 While n=0 is a special case, it is equivalent to "nosmp", 3001 which also disables the IO APIC. 3002 3003 max_loop= [LOOP] The number of loop block devices that get 3004 (loop.max_loop) unconditionally pre-created at init time. The default 3005 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 3006 of statically allocating a predefined number, loop 3007 devices can be requested on-demand with the 3008 /dev/loop-control interface. 3009 3010 mce [X86-32] Machine Check Exception 3011 3012 mce=option [X86-64] See Documentation/arch/x86/x86_64/boot-options.rst 3013 3014 md= [HW] RAID subsystems devices and level 3015 See Documentation/admin-guide/md.rst. 3016 3017 mdacon= [MDA] 3018 Format: <first>,<last> 3019 Specifies range of consoles to be captured by the MDA. 3020 3021 mds= [X86,INTEL] 3022 Control mitigation for the Micro-architectural Data 3023 Sampling (MDS) vulnerability. 3024 3025 Certain CPUs are vulnerable to an exploit against CPU 3026 internal buffers which can forward information to a 3027 disclosure gadget under certain conditions. 3028 3029 In vulnerable processors, the speculatively 3030 forwarded data can be used in a cache side channel 3031 attack, to access data to which the attacker does 3032 not have direct access. 3033 3034 This parameter controls the MDS mitigation. The 3035 options are: 3036 3037 full - Enable MDS mitigation on vulnerable CPUs 3038 full,nosmt - Enable MDS mitigation and disable 3039 SMT on vulnerable CPUs 3040 off - Unconditionally disable MDS mitigation 3041 3042 On TAA-affected machines, mds=off can be prevented by 3043 an active TAA mitigation as both vulnerabilities are 3044 mitigated with the same mechanism so in order to disable 3045 this mitigation, you need to specify tsx_async_abort=off 3046 too. 3047 3048 Not specifying this option is equivalent to 3049 mds=full. 3050 3051 For details see: Documentation/admin-guide/hw-vuln/mds.rst 3052 3053 mem=nn[KMG] [HEXAGON] Set the memory size. 3054 Must be specified, otherwise memory size will be 0. 3055 3056 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 3057 Amount of memory to be used in cases as follows: 3058 3059 1 for test; 3060 2 when the kernel is not able to see the whole system memory; 3061 3 memory that lies after 'mem=' boundary is excluded from 3062 the hypervisor, then assigned to KVM guests. 3063 4 to limit the memory available for kdump kernel. 3064 3065 [ARC,MICROBLAZE] - the limit applies only to low memory, 3066 high memory is not affected. 3067 3068 [ARM64] - only limits memory covered by the linear 3069 mapping. The NOMAP regions are not affected. 3070 3071 [X86] Work as limiting max address. Use together 3072 with memmap= to avoid physical address space collisions. 3073 Without memmap= PCI devices could be placed at addresses 3074 belonging to unused RAM. 3075 3076 Note that this only takes effects during boot time since 3077 in above case 3, memory may need be hot added after boot 3078 if system memory of hypervisor is not sufficient. 3079 3080 mem=nn[KMG]@ss[KMG] 3081 [ARM,MIPS] - override the memory layout reported by 3082 firmware. 3083 Define a memory region of size nn[KMG] starting at 3084 ss[KMG]. 3085 Multiple different regions can be specified with 3086 multiple mem= parameters on the command line. 3087 3088 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 3089 memory. 3090 3091 memblock=debug [KNL] Enable memblock debug messages. 3092 3093 memchunk=nn[KMG] 3094 [KNL,SH] Allow user to override the default size for 3095 per-device physically contiguous DMA buffers. 3096 3097 memhp_default_state=online/offline 3098 [KNL] Set the initial state for the memory hotplug 3099 onlining policy. If not specified, the default value is 3100 set according to the 3101 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 3102 option. 3103 See Documentation/admin-guide/mm/memory-hotplug.rst. 3104 3105 memmap=exactmap [KNL,X86] Enable setting of an exact 3106 E820 memory map, as specified by the user. 3107 Such memmap=exactmap lines can be constructed based on 3108 BIOS output or other requirements. See the memmap=nn@ss 3109 option description. 3110 3111 memmap=nn[KMG]@ss[KMG] 3112 [KNL, X86, MIPS, XTENSA] Force usage of a specific region of memory. 3113 Region of memory to be used is from ss to ss+nn. 3114 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 3115 which limits max address to nn[KMG]. 3116 Multiple different regions can be specified, 3117 comma delimited. 3118 Example: 3119 memmap=100M@2G,100M#3G,1G!1024G 3120 3121 memmap=nn[KMG]#ss[KMG] 3122 [KNL,ACPI] Mark specific memory as ACPI data. 3123 Region of memory to be marked is from ss to ss+nn. 3124 3125 memmap=nn[KMG]$ss[KMG] 3126 [KNL,ACPI] Mark specific memory as reserved. 3127 Region of memory to be reserved is from ss to ss+nn. 3128 Example: Exclude memory from 0x18690000-0x1869ffff 3129 memmap=64K$0x18690000 3130 or 3131 memmap=0x10000$0x18690000 3132 Some bootloaders may need an escape character before '$', 3133 like Grub2, otherwise '$' and the following number 3134 will be eaten. 3135 3136 memmap=nn[KMG]!ss[KMG] 3137 [KNL,X86] Mark specific memory as protected. 3138 Region of memory to be used, from ss to ss+nn. 3139 The memory region may be marked as e820 type 12 (0xc) 3140 and is NVDIMM or ADR memory. 3141 3142 memmap=<size>%<offset>-<oldtype>+<newtype> 3143 [KNL,ACPI] Convert memory within the specified region 3144 from <oldtype> to <newtype>. If "-<oldtype>" is left 3145 out, the whole region will be marked as <newtype>, 3146 even if previously unavailable. If "+<newtype>" is left 3147 out, matching memory will be removed. Types are 3148 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 3149 3 = ACPI, 12 = PRAM. 3150 3151 memory_corruption_check=0/1 [X86] 3152 Some BIOSes seem to corrupt the first 64k of 3153 memory when doing things like suspend/resume. 3154 Setting this option will scan the memory 3155 looking for corruption. Enabling this will 3156 both detect corruption and prevent the kernel 3157 from using the memory being corrupted. 3158 However, its intended as a diagnostic tool; if 3159 repeatable BIOS-originated corruption always 3160 affects the same memory, you can use memmap= 3161 to prevent the kernel from using that memory. 3162 3163 memory_corruption_check_size=size [X86] 3164 By default it checks for corruption in the low 3165 64k, making this memory unavailable for normal 3166 use. Use this parameter to scan for 3167 corruption in more or less memory. 3168 3169 memory_corruption_check_period=seconds [X86] 3170 By default it checks for corruption every 60 3171 seconds. Use this parameter to check at some 3172 other rate. 0 disables periodic checking. 3173 3174 memory_hotplug.memmap_on_memory 3175 [KNL,X86,ARM] Boolean flag to enable this feature. 3176 Format: {on | off (default)} 3177 When enabled, runtime hotplugged memory will 3178 allocate its internal metadata (struct pages, 3179 those vmemmap pages cannot be optimized even 3180 if hugetlb_free_vmemmap is enabled) from the 3181 hotadded memory which will allow to hotadd a 3182 lot of memory without requiring additional 3183 memory to do so. 3184 This feature is disabled by default because it 3185 has some implication on large (e.g. GB) 3186 allocations in some configurations (e.g. small 3187 memory blocks). 3188 The state of the flag can be read in 3189 /sys/module/memory_hotplug/parameters/memmap_on_memory. 3190 Note that even when enabled, there are a few cases where 3191 the feature is not effective. 3192 3193 memtest= [KNL,X86,ARM,M68K,PPC,RISCV] Enable memtest 3194 Format: <integer> 3195 default : 0 <disable> 3196 Specifies the number of memtest passes to be 3197 performed. Each pass selects another test 3198 pattern from a given set of patterns. Memtest 3199 fills the memory with this pattern, validates 3200 memory contents and reserves bad memory 3201 regions that are detected. 3202 3203 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 3204 Valid arguments: on, off 3205 Default (depends on kernel configuration option): 3206 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y) 3207 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n) 3208 mem_encrypt=on: Activate SME 3209 mem_encrypt=off: Do not activate SME 3210 3211 Refer to Documentation/virt/kvm/x86/amd-memory-encryption.rst 3212 for details on when memory encryption can be activated. 3213 3214 mem_sleep_default= [SUSPEND] Default system suspend mode: 3215 s2idle - Suspend-To-Idle 3216 shallow - Power-On Suspend or equivalent (if supported) 3217 deep - Suspend-To-RAM or equivalent (if supported) 3218 See Documentation/admin-guide/pm/sleep-states.rst. 3219 3220 mfgpt_irq= [IA-32] Specify the IRQ to use for the 3221 Multi-Function General Purpose Timers on AMD Geode 3222 platforms. 3223 3224 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 3225 the BIOS has incorrectly applied a workaround. TinyBIOS 3226 version 0.98 is known to be affected, 0.99 fixes the 3227 problem by letting the user disable the workaround. 3228 3229 mga= [HW,DRM] 3230 3231 min_addr=nn[KMG] [KNL,BOOT,IA-64] All physical memory below this 3232 physical address is ignored. 3233 3234 mini2440= [ARM,HW,KNL] 3235 Format:[0..2][b][c][t] 3236 Default: "0tb" 3237 MINI2440 configuration specification: 3238 0 - The attached screen is the 3.5" TFT 3239 1 - The attached screen is the 7" TFT 3240 2 - The VGA Shield is attached (1024x768) 3241 Leaving out the screen size parameter will not load 3242 the TFT driver, and the framebuffer will be left 3243 unconfigured. 3244 b - Enable backlight. The TFT backlight pin will be 3245 linked to the kernel VESA blanking code and a GPIO 3246 LED. This parameter is not necessary when using the 3247 VGA shield. 3248 c - Enable the s3c camera interface. 3249 t - Reserved for enabling touchscreen support. The 3250 touchscreen support is not enabled in the mainstream 3251 kernel as of 2.6.30, a preliminary port can be found 3252 in the "bleeding edge" mini2440 support kernel at 3253 https://repo.or.cz/w/linux-2.6/mini2440.git 3254 3255 mitigations= 3256 [X86,PPC,S390,ARM64] Control optional mitigations for 3257 CPU vulnerabilities. This is a set of curated, 3258 arch-independent options, each of which is an 3259 aggregation of existing arch-specific options. 3260 3261 off 3262 Disable all optional CPU mitigations. This 3263 improves system performance, but it may also 3264 expose users to several CPU vulnerabilities. 3265 Equivalent to: nopti [X86,PPC] 3266 if nokaslr then kpti=0 [ARM64] 3267 nospectre_v1 [X86,PPC] 3268 nobp=0 [S390] 3269 nospectre_v2 [X86,PPC,S390,ARM64] 3270 spectre_v2_user=off [X86] 3271 spec_store_bypass_disable=off [X86,PPC] 3272 ssbd=force-off [ARM64] 3273 nospectre_bhb [ARM64] 3274 l1tf=off [X86] 3275 mds=off [X86] 3276 tsx_async_abort=off [X86] 3277 kvm.nx_huge_pages=off [X86] 3278 srbds=off [X86,INTEL] 3279 no_entry_flush [PPC] 3280 no_uaccess_flush [PPC] 3281 mmio_stale_data=off [X86] 3282 retbleed=off [X86] 3283 3284 Exceptions: 3285 This does not have any effect on 3286 kvm.nx_huge_pages when 3287 kvm.nx_huge_pages=force. 3288 3289 auto (default) 3290 Mitigate all CPU vulnerabilities, but leave SMT 3291 enabled, even if it's vulnerable. This is for 3292 users who don't want to be surprised by SMT 3293 getting disabled across kernel upgrades, or who 3294 have other ways of avoiding SMT-based attacks. 3295 Equivalent to: (default behavior) 3296 3297 auto,nosmt 3298 Mitigate all CPU vulnerabilities, disabling SMT 3299 if needed. This is for users who always want to 3300 be fully mitigated, even if it means losing SMT. 3301 Equivalent to: l1tf=flush,nosmt [X86] 3302 mds=full,nosmt [X86] 3303 tsx_async_abort=full,nosmt [X86] 3304 mmio_stale_data=full,nosmt [X86] 3305 retbleed=auto,nosmt [X86] 3306 3307 mminit_loglevel= 3308 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 3309 parameter allows control of the logging verbosity for 3310 the additional memory initialisation checks. A value 3311 of 0 disables mminit logging and a level of 4 will 3312 log everything. Information is printed at KERN_DEBUG 3313 so loglevel=8 may also need to be specified. 3314 3315 mmio_stale_data= 3316 [X86,INTEL] Control mitigation for the Processor 3317 MMIO Stale Data vulnerabilities. 3318 3319 Processor MMIO Stale Data is a class of 3320 vulnerabilities that may expose data after an MMIO 3321 operation. Exposed data could originate or end in 3322 the same CPU buffers as affected by MDS and TAA. 3323 Therefore, similar to MDS and TAA, the mitigation 3324 is to clear the affected CPU buffers. 3325 3326 This parameter controls the mitigation. The 3327 options are: 3328 3329 full - Enable mitigation on vulnerable CPUs 3330 3331 full,nosmt - Enable mitigation and disable SMT on 3332 vulnerable CPUs. 3333 3334 off - Unconditionally disable mitigation 3335 3336 On MDS or TAA affected machines, 3337 mmio_stale_data=off can be prevented by an active 3338 MDS or TAA mitigation as these vulnerabilities are 3339 mitigated with the same mechanism so in order to 3340 disable this mitigation, you need to specify 3341 mds=off and tsx_async_abort=off too. 3342 3343 Not specifying this option is equivalent to 3344 mmio_stale_data=full. 3345 3346 For details see: 3347 Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst 3348 3349 <module>.async_probe[=<bool>] [KNL] 3350 If no <bool> value is specified or if the value 3351 specified is not a valid <bool>, enable asynchronous 3352 probe on this module. Otherwise, enable/disable 3353 asynchronous probe on this module as indicated by the 3354 <bool> value. See also: module.async_probe 3355 3356 module.async_probe=<bool> 3357 [KNL] When set to true, modules will use async probing 3358 by default. To enable/disable async probing for a 3359 specific module, use the module specific control that 3360 is documented under <module>.async_probe. When both 3361 module.async_probe and <module>.async_probe are 3362 specified, <module>.async_probe takes precedence for 3363 the specific module. 3364 3365 module.enable_dups_trace 3366 [KNL] When CONFIG_MODULE_DEBUG_AUTOLOAD_DUPS is set, 3367 this means that duplicate request_module() calls will 3368 trigger a WARN_ON() instead of a pr_warn(). Note that 3369 if MODULE_DEBUG_AUTOLOAD_DUPS_TRACE is set, WARN_ON()s 3370 will always be issued and this option does nothing. 3371 module.sig_enforce 3372 [KNL] When CONFIG_MODULE_SIG is set, this means that 3373 modules without (valid) signatures will fail to load. 3374 Note that if CONFIG_MODULE_SIG_FORCE is set, that 3375 is always true, so this option does nothing. 3376 3377 module_blacklist= [KNL] Do not load a comma-separated list of 3378 modules. Useful for debugging problem modules. 3379 3380 mousedev.tap_time= 3381 [MOUSE] Maximum time between finger touching and 3382 leaving touchpad surface for touch to be considered 3383 a tap and be reported as a left button click (for 3384 touchpads working in absolute mode only). 3385 Format: <msecs> 3386 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 3387 reporting absolute coordinates, such as tablets 3388 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 3389 reporting absolute coordinates, such as tablets 3390 3391 movablecore= [KNL,X86,IA-64,PPC] 3392 Format: nn[KMGTPE] | nn% 3393 This parameter is the complement to kernelcore=, it 3394 specifies the amount of memory used for migratable 3395 allocations. If both kernelcore and movablecore is 3396 specified, then kernelcore will be at *least* the 3397 specified value but may be more. If movablecore on its 3398 own is specified, the administrator must be careful 3399 that the amount of memory usable for all allocations 3400 is not too small. 3401 3402 movable_node [KNL] Boot-time switch to make hotplugable memory 3403 NUMA nodes to be movable. This means that the memory 3404 of such nodes will be usable only for movable 3405 allocations which rules out almost all kernel 3406 allocations. Use with caution! 3407 3408 MTD_Partition= [MTD] 3409 Format: <name>,<region-number>,<size>,<offset> 3410 3411 MTD_Region= [MTD] Format: 3412 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 3413 3414 mtdparts= [MTD] 3415 See drivers/mtd/parsers/cmdlinepart.c 3416 3417 mtdset= [ARM] 3418 ARM/S3C2412 JIVE boot control 3419 3420 See arch/arm/mach-s3c/mach-jive.c 3421 3422 mtouchusb.raw_coordinates= 3423 [HW] Make the MicroTouch USB driver use raw coordinates 3424 ('y', default) or cooked coordinates ('n') 3425 3426 mtrr_chunk_size=nn[KMG] [X86] 3427 used for mtrr cleanup. It is largest continuous chunk 3428 that could hold holes aka. UC entries. 3429 3430 mtrr_gran_size=nn[KMG] [X86] 3431 Used for mtrr cleanup. It is granularity of mtrr block. 3432 Default is 1. 3433 Large value could prevent small alignment from 3434 using up MTRRs. 3435 3436 mtrr_spare_reg_nr=n [X86] 3437 Format: <integer> 3438 Range: 0,7 : spare reg number 3439 Default : 1 3440 Used for mtrr cleanup. It is spare mtrr entries number. 3441 Set to 2 or more if your graphical card needs more. 3442 3443 multitce=off [PPC] This parameter disables the use of the pSeries 3444 firmware feature for updating multiple TCE entries 3445 at a time. 3446 3447 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 3448 3449 netdev= [NET] Network devices parameters 3450 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 3451 Note that mem_start is often overloaded to mean 3452 something different and driver-specific. 3453 This usage is only documented in each driver source 3454 file if at all. 3455 3456 netpoll.carrier_timeout= 3457 [NET] Specifies amount of time (in seconds) that 3458 netpoll should wait for a carrier. By default netpoll 3459 waits 4 seconds. 3460 3461 nf_conntrack.acct= 3462 [NETFILTER] Enable connection tracking flow accounting 3463 0 to disable accounting 3464 1 to enable accounting 3465 Default value is 0. 3466 3467 nfs.cache_getent= 3468 [NFS] sets the pathname to the program which is used 3469 to update the NFS client cache entries. 3470 3471 nfs.cache_getent_timeout= 3472 [NFS] sets the timeout after which an attempt to 3473 update a cache entry is deemed to have failed. 3474 3475 nfs.callback_nr_threads= 3476 [NFSv4] set the total number of threads that the 3477 NFS client will assign to service NFSv4 callback 3478 requests. 3479 3480 nfs.callback_tcpport= 3481 [NFS] set the TCP port on which the NFSv4 callback 3482 channel should listen. 3483 3484 nfs.enable_ino64= 3485 [NFS] enable 64-bit inode numbers. 3486 If zero, the NFS client will fake up a 32-bit inode 3487 number for the readdir() and stat() syscalls instead 3488 of returning the full 64-bit number. 3489 The default is to return 64-bit inode numbers. 3490 3491 nfs.idmap_cache_timeout= 3492 [NFS] set the maximum lifetime for idmapper cache 3493 entries. 3494 3495 nfs.max_session_cb_slots= 3496 [NFSv4.1] Sets the maximum number of session 3497 slots the client will assign to the callback 3498 channel. This determines the maximum number of 3499 callbacks the client will process in parallel for 3500 a particular server. 3501 3502 nfs.max_session_slots= 3503 [NFSv4.1] Sets the maximum number of session slots 3504 the client will attempt to negotiate with the server. 3505 This limits the number of simultaneous RPC requests 3506 that the client can send to the NFSv4.1 server. 3507 Note that there is little point in setting this 3508 value higher than the max_tcp_slot_table_limit. 3509 3510 nfs.nfs4_disable_idmapping= 3511 [NFSv4] When set to the default of '1', this option 3512 ensures that both the RPC level authentication 3513 scheme and the NFS level operations agree to use 3514 numeric uids/gids if the mount is using the 3515 'sec=sys' security flavour. In effect it is 3516 disabling idmapping, which can make migration from 3517 legacy NFSv2/v3 systems to NFSv4 easier. 3518 Servers that do not support this mode of operation 3519 will be autodetected by the client, and it will fall 3520 back to using the idmapper. 3521 To turn off this behaviour, set the value to '0'. 3522 3523 nfs.nfs4_unique_id= 3524 [NFS4] Specify an additional fixed unique ident- 3525 ification string that NFSv4 clients can insert into 3526 their nfs_client_id4 string. This is typically a 3527 UUID that is generated at system install time. 3528 3529 nfs.recover_lost_locks= 3530 [NFSv4] Attempt to recover locks that were lost due 3531 to a lease timeout on the server. Please note that 3532 doing this risks data corruption, since there are 3533 no guarantees that the file will remain unchanged 3534 after the locks are lost. 3535 If you want to enable the kernel legacy behaviour of 3536 attempting to recover these locks, then set this 3537 parameter to '1'. 3538 The default parameter value of '0' causes the kernel 3539 not to attempt recovery of lost locks. 3540 3541 nfs.send_implementation_id= 3542 [NFSv4.1] Send client implementation identification 3543 information in exchange_id requests. 3544 If zero, no implementation identification information 3545 will be sent. 3546 The default is to send the implementation identification 3547 information. 3548 3549 nfs4.layoutstats_timer= 3550 [NFSv4.2] Change the rate at which the kernel sends 3551 layoutstats to the pNFS metadata server. 3552 3553 Setting this to value to 0 causes the kernel to use 3554 whatever value is the default set by the layout 3555 driver. A non-zero value sets the minimum interval 3556 in seconds between layoutstats transmissions. 3557 3558 nfsd.inter_copy_offload_enable= 3559 [NFSv4.2] When set to 1, the server will support 3560 server-to-server copies for which this server is 3561 the destination of the copy. 3562 3563 nfsd.nfs4_disable_idmapping= 3564 [NFSv4] When set to the default of '1', the NFSv4 3565 server will return only numeric uids and gids to 3566 clients using auth_sys, and will accept numeric uids 3567 and gids from such clients. This is intended to ease 3568 migration from NFSv2/v3. 3569 3570 nfsd.nfsd4_ssc_umount_timeout= 3571 [NFSv4.2] When used as the destination of a 3572 server-to-server copy, knfsd temporarily mounts 3573 the source server. It caches the mount in case 3574 it will be needed again, and discards it if not 3575 used for the number of milliseconds specified by 3576 this parameter. 3577 3578 nfsaddrs= [NFS] Deprecated. Use ip= instead. 3579 See Documentation/admin-guide/nfs/nfsroot.rst. 3580 3581 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 3582 See Documentation/admin-guide/nfs/nfsroot.rst. 3583 3584 nfsrootdebug [NFS] enable nfsroot debugging messages. 3585 See Documentation/admin-guide/nfs/nfsroot.rst. 3586 3587 nmi_backtrace.backtrace_idle [KNL] 3588 Dump stacks even of idle CPUs in response to an 3589 NMI stack-backtrace request. 3590 3591 nmi_debug= [KNL,SH] Specify one or more actions to take 3592 when a NMI is triggered. 3593 Format: [state][,regs][,debounce][,die] 3594 3595 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 3596 Format: [panic,][nopanic,][num] 3597 Valid num: 0 or 1 3598 0 - turn hardlockup detector in nmi_watchdog off 3599 1 - turn hardlockup detector in nmi_watchdog on 3600 When panic is specified, panic when an NMI watchdog 3601 timeout occurs (or 'nopanic' to not panic on an NMI 3602 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 3603 To disable both hard and soft lockup detectors, 3604 please see 'nowatchdog'. 3605 This is useful when you use a panic=... timeout and 3606 need the box quickly up again. 3607 3608 These settings can be accessed at runtime via 3609 the nmi_watchdog and hardlockup_panic sysctls. 3610 3611 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 3612 emulation library even if a 387 maths coprocessor 3613 is present. 3614 3615 no4lvl [RISCV] Disable 4-level and 5-level paging modes. Forces 3616 kernel to use 3-level paging instead. 3617 3618 no5lvl [X86-64,RISCV] Disable 5-level paging mode. Forces 3619 kernel to use 4-level paging instead. 3620 3621 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 3622 caches in the slab allocator. Saves per-node memory, 3623 but will impact performance. 3624 3625 noalign [KNL,ARM] 3626 3627 noaltinstr [S390] Disables alternative instructions patching 3628 (CPU alternatives feature). 3629 3630 noapic [SMP,APIC] Tells the kernel to not make use of any 3631 IOAPICs that may be present in the system. 3632 3633 noautogroup Disable scheduler automatic task group creation. 3634 3635 nocache [ARM] 3636 3637 no_console_suspend 3638 [HW] Never suspend the console 3639 Disable suspending of consoles during suspend and 3640 hibernate operations. Once disabled, debugging 3641 messages can reach various consoles while the rest 3642 of the system is being put to sleep (ie, while 3643 debugging driver suspend/resume hooks). This may 3644 not work reliably with all consoles, but is known 3645 to work with serial and VGA consoles. 3646 To facilitate more flexible debugging, we also add 3647 console_suspend, a printk module parameter to control 3648 it. Users could use console_suspend (usually 3649 /sys/module/printk/parameters/console_suspend) to 3650 turn on/off it dynamically. 3651 3652 no_debug_objects 3653 [KNL] Disable object debugging 3654 3655 nodsp [SH] Disable hardware DSP at boot time. 3656 3657 noefi Disable EFI runtime services support. 3658 3659 no_entry_flush [PPC] Don't flush the L1-D cache when entering the kernel. 3660 3661 noexec [IA-64] 3662 3663 noexec32 [X86-64] 3664 This affects only 32-bit executables. 3665 noexec32=on: enable non-executable mappings (default) 3666 read doesn't imply executable mappings 3667 noexec32=off: disable non-executable mappings 3668 read implies executable mappings 3669 3670 no_file_caps Tells the kernel not to honor file capabilities. The 3671 only way then for a file to be executed with privilege 3672 is to be setuid root or executed by root. 3673 3674 nofpu [MIPS,SH] Disable hardware FPU at boot time. 3675 3676 nofsgsbase [X86] Disables FSGSBASE instructions. 3677 3678 nofxsr [BUGS=X86-32] Disables x86 floating point extended 3679 register save and restore. The kernel will only save 3680 legacy floating-point registers on task switch. 3681 3682 nohalt [IA-64] Tells the kernel not to use the power saving 3683 function PAL_HALT_LIGHT when idle. This increases 3684 power-consumption. On the positive side, it reduces 3685 interrupt wake-up latency, which may improve performance 3686 in certain environments such as networked servers or 3687 real-time systems. 3688 3689 no_hash_pointers 3690 Force pointers printed to the console or buffers to be 3691 unhashed. By default, when a pointer is printed via %p 3692 format string, that pointer is "hashed", i.e. obscured 3693 by hashing the pointer value. This is a security feature 3694 that hides actual kernel addresses from unprivileged 3695 users, but it also makes debugging the kernel more 3696 difficult since unequal pointers can no longer be 3697 compared. However, if this command-line option is 3698 specified, then all normal pointers will have their true 3699 value printed. This option should only be specified when 3700 debugging the kernel. Please do not use on production 3701 kernels. 3702 3703 nohibernate [HIBERNATION] Disable hibernation and resume. 3704 3705 nohlt [ARM,ARM64,MICROBLAZE,SH] Forces the kernel to busy wait 3706 in do_idle() and not use the arch_cpu_idle() 3707 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP 3708 to be effective. This is useful on platforms where the 3709 sleep(SH) or wfi(ARM,ARM64) instructions do not work 3710 correctly or when doing power measurements to evaluate 3711 the impact of the sleep instructions. This is also 3712 useful when using JTAG debugger. 3713 3714 nohugeiomap [KNL,X86,PPC,ARM64] Disable kernel huge I/O mappings. 3715 3716 nohugevmalloc [KNL,X86,PPC,ARM64] Disable kernel huge vmalloc mappings. 3717 3718 nohz= [KNL] Boottime enable/disable dynamic ticks 3719 Valid arguments: on, off 3720 Default: on 3721 3722 nohz_full= [KNL,BOOT,SMP,ISOL] 3723 The argument is a cpu list, as described above. 3724 In kernels built with CONFIG_NO_HZ_FULL=y, set 3725 the specified list of CPUs whose tick will be stopped 3726 whenever possible. The boot CPU will be forced outside 3727 the range to maintain the timekeeping. Any CPUs 3728 in this list will have their RCU callbacks offloaded, 3729 just as if they had also been called out in the 3730 rcu_nocbs= boot parameter. 3731 3732 Note that this argument takes precedence over 3733 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. 3734 3735 noinitrd [RAM] Tells the kernel not to load any configured 3736 initial RAM disk. 3737 3738 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 3739 remapping. 3740 [Deprecated - use intremap=off] 3741 3742 nointroute [IA-64] 3743 3744 noinvpcid [X86] Disable the INVPCID cpu feature. 3745 3746 noiotrap [SH] Disables trapped I/O port accesses. 3747 3748 noirqdebug [X86-32] Disables the code which attempts to detect and 3749 disable unhandled interrupt sources. 3750 3751 noisapnp [ISAPNP] Disables ISA PnP code. 3752 3753 nojitter [IA-64] Disables jitter checking for ITC timers. 3754 3755 nokaslr [KNL] 3756 When CONFIG_RANDOMIZE_BASE is set, this disables 3757 kernel and module base offset ASLR (Address Space 3758 Layout Randomization). 3759 3760 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 3761 fault handling. 3762 3763 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 3764 3765 nolapic [X86-32,APIC] Do not enable or use the local APIC. 3766 3767 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 3768 3769 nomca [IA-64] Disable machine check abort handling 3770 3771 nomce [X86-32] Disable Machine Check Exception 3772 3773 nomfgpt [X86-32] Disable Multi-Function General Purpose 3774 Timer usage (for AMD Geode machines). 3775 3776 nomodeset Disable kernel modesetting. Most systems' firmware 3777 sets up a display mode and provides framebuffer memory 3778 for output. With nomodeset, DRM and fbdev drivers will 3779 not load if they could possibly displace the pre- 3780 initialized output. Only the system framebuffer will 3781 be available for use. The respective drivers will not 3782 perform display-mode changes or accelerated rendering. 3783 3784 Useful as error fallback, or for testing and debugging. 3785 3786 nomodule Disable module load 3787 3788 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 3789 shutdown the other cpus. Instead use the REBOOT_VECTOR 3790 irq. 3791 3792 nopat [X86] Disable PAT (page attribute table extension of 3793 pagetables) support. 3794 3795 nopcid [X86-64] Disable the PCID cpu feature. 3796 3797 nopku [X86] Disable Memory Protection Keys CPU feature found 3798 in some Intel CPUs. 3799 3800 nopti [X86-64] 3801 Equivalent to pti=off 3802 3803 nopv= [X86,XEN,KVM,HYPER_V,VMWARE] 3804 Disables the PV optimizations forcing the guest to run 3805 as generic guest with no PV drivers. Currently support 3806 XEN HVM, KVM, HYPER_V and VMWARE guest. 3807 3808 nopvspin [X86,XEN,KVM] 3809 Disables the qspinlock slow path using PV optimizations 3810 which allow the hypervisor to 'idle' the guest on lock 3811 contention. 3812 3813 norandmaps Don't use address space randomization. Equivalent to 3814 echo 0 > /proc/sys/kernel/randomize_va_space 3815 3816 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 3817 with UP alternatives 3818 3819 noresume [SWSUSP] Disables resume and restores original swap 3820 space. 3821 3822 nosbagart [IA-64] 3823 3824 no-scroll [VGA] Disables scrollback. 3825 This is required for the Braillex ib80-piezo Braille 3826 reader made by F.H. Papenmeier (Germany). 3827 3828 nosgx [X86-64,SGX] Disables Intel SGX kernel support. 3829 3830 nosmap [PPC] 3831 Disable SMAP (Supervisor Mode Access Prevention) 3832 even if it is supported by processor. 3833 3834 nosmep [PPC64s] 3835 Disable SMEP (Supervisor Mode Execution Prevention) 3836 even if it is supported by processor. 3837 3838 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 3839 and disable the IO APIC. legacy for "maxcpus=0". 3840 3841 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 3842 Equivalent to smt=1. 3843 3844 [KNL,X86] Disable symmetric multithreading (SMT). 3845 nosmt=force: Force disable SMT, cannot be undone 3846 via the sysfs control file. 3847 3848 nosoftlockup [KNL] Disable the soft-lockup detector. 3849 3850 nospec_store_bypass_disable 3851 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability 3852 3853 nospectre_bhb [ARM64] Disable all mitigations for Spectre-BHB (branch 3854 history injection) vulnerability. System may allow data leaks 3855 with this option. 3856 3857 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1 3858 (bounds check bypass). With this option data leaks are 3859 possible in the system. 3860 3861 nospectre_v2 [X86,PPC_E500,ARM64] Disable all mitigations for 3862 the Spectre variant 2 (indirect branch prediction) 3863 vulnerability. System may allow data leaks with this 3864 option. 3865 3866 no-steal-acc [X86,PV_OPS,ARM64,PPC/PSERIES] Disable paravirtualized 3867 steal time accounting. steal time is computed, but 3868 won't influence scheduler behaviour 3869 3870 nosync [HW,M68K] Disables sync negotiation for all devices. 3871 3872 no_timer_check [X86,APIC] Disables the code which tests for 3873 broken timer IRQ sources. 3874 3875 no_uaccess_flush 3876 [PPC] Don't flush the L1-D cache after accessing user data. 3877 3878 novmcoredd [KNL,KDUMP] 3879 Disable device dump. Device dump allows drivers to 3880 append dump data to vmcore so you can collect driver 3881 specified debug info. Drivers can append the data 3882 without any limit and this data is stored in memory, 3883 so this may cause significant memory stress. Disabling 3884 device dump can help save memory but the driver debug 3885 data will be no longer available. This parameter 3886 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 3887 is set. 3888 3889 no-vmw-sched-clock 3890 [X86,PV_OPS] Disable paravirtualized VMware scheduler 3891 clock and use the default one. 3892 3893 nowatchdog [KNL] Disable both lockup detectors, i.e. 3894 soft-lockup and NMI watchdog (hard-lockup). 3895 3896 nowb [ARM] 3897 3898 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 3899 3900 NOTE: this parameter will be ignored on systems with the 3901 LEGACY_XAPIC_DISABLED bit set in the 3902 IA32_XAPIC_DISABLE_STATUS MSR. 3903 3904 noxsave [BUGS=X86] Disables x86 extended register state save 3905 and restore using xsave. The kernel will fallback to 3906 enabling legacy floating-point and sse state. 3907 3908 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 3909 register states. The kernel will fall back to use 3910 xsave to save the states. By using this parameter, 3911 performance of saving the states is degraded because 3912 xsave doesn't support modified optimization while 3913 xsaveopt supports it on xsaveopt enabled systems. 3914 3915 noxsaves [X86] Disables xsaves and xrstors used in saving and 3916 restoring x86 extended register state in compacted 3917 form of xsave area. The kernel will fall back to use 3918 xsaveopt and xrstor to save and restore the states 3919 in standard form of xsave area. By using this 3920 parameter, xsave area per process might occupy more 3921 memory on xsaves enabled systems. 3922 3923 nps_mtm_hs_ctr= [KNL,ARC] 3924 This parameter sets the maximum duration, in 3925 cycles, each HW thread of the CTOP can run 3926 without interruptions, before HW switches it. 3927 The actual maximum duration is 16 times this 3928 parameter's value. 3929 Format: integer between 1 and 255 3930 Default: 255 3931 3932 nptcg= [IA-64] Override max number of concurrent global TLB 3933 purges which is reported from either PAL_VM_SUMMARY or 3934 SAL PALO. 3935 3936 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 3937 could support. nr_cpus=n : n >= 1 limits the kernel to 3938 support 'n' processors. It could be larger than the 3939 number of already plugged CPU during bootup, later in 3940 runtime you can physically add extra cpu until it reaches 3941 n. So during boot up some boot time memory for per-cpu 3942 variables need be pre-allocated for later physical cpu 3943 hot plugging. 3944 3945 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 3946 3947 numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86] Disable NUMA, Only 3948 set up a single NUMA node spanning all memory. 3949 3950 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic 3951 NUMA balancing. 3952 Allowed values are enable and disable 3953 3954 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 3955 'node', 'default' can be specified 3956 This can be set from sysctl after boot. 3957 See Documentation/admin-guide/sysctl/vm.rst for details. 3958 3959 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 3960 See Documentation/core-api/debugging-via-ohci1394.rst for more 3961 info. 3962 3963 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 3964 Rather than timing out after 20 ms if an EC 3965 command is not properly ACKed, override the length 3966 of the timeout. We have interrupts disabled while 3967 waiting for the ACK, so if this is set too high 3968 interrupts *may* be lost! 3969 3970 omap_mux= [OMAP] Override bootloader pin multiplexing. 3971 Format: <mux_mode0.mode_name=value>... 3972 For example, to override I2C bus2: 3973 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 3974 3975 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 3976 3977 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 3978 3979 boundary - index of last SLC block on Flex-OneNAND. 3980 The remaining blocks are configured as MLC blocks. 3981 lock - Configure if Flex-OneNAND boundary should be locked. 3982 Once locked, the boundary cannot be changed. 3983 1 indicates lock status, 0 indicates unlock status. 3984 3985 oops=panic Always panic on oopses. Default is to just kill the 3986 process, but there is a small probability of 3987 deadlocking the machine. 3988 This will also cause panics on machine check exceptions. 3989 Useful together with panic=30 to trigger a reboot. 3990 3991 page_alloc.shuffle= 3992 [KNL] Boolean flag to control whether the page allocator 3993 should randomize its free lists. The randomization may 3994 be automatically enabled if the kernel detects it is 3995 running on a platform with a direct-mapped memory-side 3996 cache, and this parameter can be used to 3997 override/disable that behavior. The state of the flag 3998 can be read from sysfs at: 3999 /sys/module/page_alloc/parameters/shuffle. 4000 4001 page_owner= [KNL] Boot-time page_owner enabling option. 4002 Storage of the information about who allocated 4003 each page is disabled in default. With this switch, 4004 we can turn it on. 4005 on: enable the feature 4006 4007 page_poison= [KNL] Boot-time parameter changing the state of 4008 poisoning on the buddy allocator, available with 4009 CONFIG_PAGE_POISONING=y. 4010 off: turn off poisoning (default) 4011 on: turn on poisoning 4012 4013 page_reporting.page_reporting_order= 4014 [KNL] Minimal page reporting order 4015 Format: <integer> 4016 Adjust the minimal page reporting order. The page 4017 reporting is disabled when it exceeds MAX_ORDER. 4018 4019 panic= [KNL] Kernel behaviour on panic: delay <timeout> 4020 timeout > 0: seconds before rebooting 4021 timeout = 0: wait forever 4022 timeout < 0: reboot immediately 4023 Format: <timeout> 4024 4025 panic_print= Bitmask for printing system info when panic happens. 4026 User can chose combination of the following bits: 4027 bit 0: print all tasks info 4028 bit 1: print system memory info 4029 bit 2: print timer info 4030 bit 3: print locks info if CONFIG_LOCKDEP is on 4031 bit 4: print ftrace buffer 4032 bit 5: print all printk messages in buffer 4033 bit 6: print all CPUs backtrace (if available in the arch) 4034 *Be aware* that this option may print a _lot_ of lines, 4035 so there are risks of losing older messages in the log. 4036 Use this option carefully, maybe worth to setup a 4037 bigger log buffer with "log_buf_len" along with this. 4038 4039 panic_on_taint= Bitmask for conditionally calling panic() in add_taint() 4040 Format: <hex>[,nousertaint] 4041 Hexadecimal bitmask representing the set of TAINT flags 4042 that will cause the kernel to panic when add_taint() is 4043 called with any of the flags in this set. 4044 The optional switch "nousertaint" can be utilized to 4045 prevent userspace forced crashes by writing to sysctl 4046 /proc/sys/kernel/tainted any flagset matching with the 4047 bitmask set on panic_on_taint. 4048 See Documentation/admin-guide/tainted-kernels.rst for 4049 extra details on the taint flags that users can pick 4050 to compose the bitmask to assign to panic_on_taint. 4051 4052 panic_on_warn panic() instead of WARN(). Useful to cause kdump 4053 on a WARN(). 4054 4055 parkbd.port= [HW] Parallel port number the keyboard adapter is 4056 connected to, default is 0. 4057 Format: <parport#> 4058 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 4059 0 for XT, 1 for AT (default is AT). 4060 Format: <mode> 4061 4062 parport= [HW,PPT] Specify parallel ports. 0 disables. 4063 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 4064 Use 'auto' to force the driver to use any 4065 IRQ/DMA settings detected (the default is to 4066 ignore detected IRQ/DMA settings because of 4067 possible conflicts). You can specify the base 4068 address, IRQ, and DMA settings; IRQ and DMA 4069 should be numbers, or 'auto' (for using detected 4070 settings on that particular port), or 'nofifo' 4071 (to avoid using a FIFO even if it is detected). 4072 Parallel ports are assigned in the order they 4073 are specified on the command line, starting 4074 with parport0. 4075 4076 parport_init_mode= [HW,PPT] 4077 Configure VIA parallel port to operate in 4078 a specific mode. This is necessary on Pegasos 4079 computer where firmware has no options for setting 4080 up parallel port mode and sets it to spp. 4081 Currently this function knows 686a and 8231 chips. 4082 Format: [spp|ps2|epp|ecp|ecpepp] 4083 4084 pata_legacy.all= [HW,LIBATA] 4085 Format: <int> 4086 Set to non-zero to probe primary and secondary ISA 4087 port ranges on PCI systems where no PCI PATA device 4088 has been found at either range. Disabled by default. 4089 4090 pata_legacy.autospeed= [HW,LIBATA] 4091 Format: <int> 4092 Set to non-zero if a chip is present that snoops speed 4093 changes. Disabled by default. 4094 4095 pata_legacy.ht6560a= [HW,LIBATA] 4096 Format: <int> 4097 Set to 1, 2, or 3 for HT 6560A on the primary channel, 4098 the secondary channel, or both channels respectively. 4099 Disabled by default. 4100 4101 pata_legacy.ht6560b= [HW,LIBATA] 4102 Format: <int> 4103 Set to 1, 2, or 3 for HT 6560B on the primary channel, 4104 the secondary channel, or both channels respectively. 4105 Disabled by default. 4106 4107 pata_legacy.iordy_mask= [HW,LIBATA] 4108 Format: <int> 4109 IORDY enable mask. Set individual bits to allow IORDY 4110 for the respective channel. Bit 0 is for the first 4111 legacy channel handled by this driver, bit 1 is for 4112 the second channel, and so on. The sequence will often 4113 correspond to the primary legacy channel, the secondary 4114 legacy channel, and so on, but the handling of a PCI 4115 bus and the use of other driver options may interfere 4116 with the sequence. By default IORDY is allowed across 4117 all channels. 4118 4119 pata_legacy.opti82c46x= [HW,LIBATA] 4120 Format: <int> 4121 Set to 1, 2, or 3 for Opti 82c611A on the primary 4122 channel, the secondary channel, or both channels 4123 respectively. Disabled by default. 4124 4125 pata_legacy.opti82c611a= [HW,LIBATA] 4126 Format: <int> 4127 Set to 1, 2, or 3 for Opti 82c465MV on the primary 4128 channel, the secondary channel, or both channels 4129 respectively. Disabled by default. 4130 4131 pata_legacy.pio_mask= [HW,LIBATA] 4132 Format: <int> 4133 PIO mode mask for autospeed devices. Set individual 4134 bits to allow the use of the respective PIO modes. 4135 Bit 0 is for mode 0, bit 1 is for mode 1, and so on. 4136 All modes allowed by default. 4137 4138 pata_legacy.probe_all= [HW,LIBATA] 4139 Format: <int> 4140 Set to non-zero to probe tertiary and further ISA 4141 port ranges on PCI systems. Disabled by default. 4142 4143 pata_legacy.probe_mask= [HW,LIBATA] 4144 Format: <int> 4145 Probe mask for legacy ISA PATA ports. Depending on 4146 platform configuration and the use of other driver 4147 options up to 6 legacy ports are supported: 0x1f0, 4148 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing 4149 of individual ports can be disabled by setting the 4150 corresponding bits in the mask to 1. Bit 0 is for 4151 the first port in the list above (0x1f0), and so on. 4152 By default all supported ports are probed. 4153 4154 pata_legacy.qdi= [HW,LIBATA] 4155 Format: <int> 4156 Set to non-zero to probe QDI controllers. By default 4157 set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise. 4158 4159 pata_legacy.winbond= [HW,LIBATA] 4160 Format: <int> 4161 Set to non-zero to probe Winbond controllers. Use 4162 the standard I/O port (0x130) if 1, otherwise the 4163 value given is the I/O port to use (typically 0x1b0). 4164 By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE, 4165 0 otherwise. 4166 4167 pata_platform.pio_mask= [HW,LIBATA] 4168 Format: <int> 4169 Supported PIO mode mask. Set individual bits to allow 4170 the use of the respective PIO modes. Bit 0 is for 4171 mode 0, bit 1 is for mode 1, and so on. Mode 0 only 4172 allowed by default. 4173 4174 pause_on_oops= 4175 Halt all CPUs after the first oops has been printed for 4176 the specified number of seconds. This is to be used if 4177 your oopses keep scrolling off the screen. 4178 4179 pcbit= [HW,ISDN] 4180 4181 pci=option[,option...] [PCI] various PCI subsystem options. 4182 4183 Some options herein operate on a specific device 4184 or a set of devices (<pci_dev>). These are 4185 specified in one of the following formats: 4186 4187 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 4188 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 4189 4190 Note: the first format specifies a PCI 4191 bus/device/function address which may change 4192 if new hardware is inserted, if motherboard 4193 firmware changes, or due to changes caused 4194 by other kernel parameters. If the 4195 domain is left unspecified, it is 4196 taken to be zero. Optionally, a path 4197 to a device through multiple device/function 4198 addresses can be specified after the base 4199 address (this is more robust against 4200 renumbering issues). The second format 4201 selects devices using IDs from the 4202 configuration space which may match multiple 4203 devices in the system. 4204 4205 earlydump dump PCI config space before the kernel 4206 changes anything 4207 off [X86] don't probe for the PCI bus 4208 bios [X86-32] force use of PCI BIOS, don't access 4209 the hardware directly. Use this if your machine 4210 has a non-standard PCI host bridge. 4211 nobios [X86-32] disallow use of PCI BIOS, only direct 4212 hardware access methods are allowed. Use this 4213 if you experience crashes upon bootup and you 4214 suspect they are caused by the BIOS. 4215 conf1 [X86] Force use of PCI Configuration Access 4216 Mechanism 1 (config address in IO port 0xCF8, 4217 data in IO port 0xCFC, both 32-bit). 4218 conf2 [X86] Force use of PCI Configuration Access 4219 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 4220 the function, IO port 0xCFA, also 8-bit, sets 4221 bus number. The config space is then accessed 4222 through ports 0xC000-0xCFFF). 4223 See http://wiki.osdev.org/PCI for more info 4224 on the configuration access mechanisms. 4225 noaer [PCIE] If the PCIEAER kernel config parameter is 4226 enabled, this kernel boot option can be used to 4227 disable the use of PCIE advanced error reporting. 4228 nodomains [PCI] Disable support for multiple PCI 4229 root domains (aka PCI segments, in ACPI-speak). 4230 nommconf [X86] Disable use of MMCONFIG for PCI 4231 Configuration 4232 check_enable_amd_mmconf [X86] check for and enable 4233 properly configured MMIO access to PCI 4234 config space on AMD family 10h CPU 4235 nomsi [MSI] If the PCI_MSI kernel config parameter is 4236 enabled, this kernel boot option can be used to 4237 disable the use of MSI interrupts system-wide. 4238 noioapicquirk [APIC] Disable all boot interrupt quirks. 4239 Safety option to keep boot IRQs enabled. This 4240 should never be necessary. 4241 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 4242 primary IO-APIC for bridges that cannot disable 4243 boot IRQs. This fixes a source of spurious IRQs 4244 when the system masks IRQs. 4245 noioapicreroute [APIC] Disable workaround that uses the 4246 boot IRQ equivalent of an IRQ that connects to 4247 a chipset where boot IRQs cannot be disabled. 4248 The opposite of ioapicreroute. 4249 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 4250 routing table. These calls are known to be buggy 4251 on several machines and they hang the machine 4252 when used, but on other computers it's the only 4253 way to get the interrupt routing table. Try 4254 this option if the kernel is unable to allocate 4255 IRQs or discover secondary PCI buses on your 4256 motherboard. 4257 rom [X86] Assign address space to expansion ROMs. 4258 Use with caution as certain devices share 4259 address decoders between ROMs and other 4260 resources. 4261 norom [X86] Do not assign address space to 4262 expansion ROMs that do not already have 4263 BIOS assigned address ranges. 4264 nobar [X86] Do not assign address space to the 4265 BARs that weren't assigned by the BIOS. 4266 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 4267 assigned automatically to PCI devices. You can 4268 make the kernel exclude IRQs of your ISA cards 4269 this way. 4270 pirqaddr=0xAAAAA [X86] Specify the physical address 4271 of the PIRQ table (normally generated 4272 by the BIOS) if it is outside the 4273 F0000h-100000h range. 4274 lastbus=N [X86] Scan all buses thru bus #N. Can be 4275 useful if the kernel is unable to find your 4276 secondary buses and you want to tell it 4277 explicitly which ones they are. 4278 assign-busses [X86] Always assign all PCI bus 4279 numbers ourselves, overriding 4280 whatever the firmware may have done. 4281 usepirqmask [X86] Honor the possible IRQ mask stored 4282 in the BIOS $PIR table. This is needed on 4283 some systems with broken BIOSes, notably 4284 some HP Pavilion N5400 and Omnibook XE3 4285 notebooks. This will have no effect if ACPI 4286 IRQ routing is enabled. 4287 noacpi [X86] Do not use ACPI for IRQ routing 4288 or for PCI scanning. 4289 use_crs [X86] Use PCI host bridge window information 4290 from ACPI. On BIOSes from 2008 or later, this 4291 is enabled by default. If you need to use this, 4292 please report a bug. 4293 nocrs [X86] Ignore PCI host bridge windows from ACPI. 4294 If you need to use this, please report a bug. 4295 use_e820 [X86] Use E820 reservations to exclude parts of 4296 PCI host bridge windows. This is a workaround 4297 for BIOS defects in host bridge _CRS methods. 4298 If you need to use this, please report a bug to 4299 <linux-pci@vger.kernel.org>. 4300 no_e820 [X86] Ignore E820 reservations for PCI host 4301 bridge windows. This is the default on modern 4302 hardware. If you need to use this, please report 4303 a bug to <linux-pci@vger.kernel.org>. 4304 routeirq Do IRQ routing for all PCI devices. 4305 This is normally done in pci_enable_device(), 4306 so this option is a temporary workaround 4307 for broken drivers that don't call it. 4308 skip_isa_align [X86] do not align io start addr, so can 4309 handle more pci cards 4310 noearly [X86] Don't do any early type 1 scanning. 4311 This might help on some broken boards which 4312 machine check when some devices' config space 4313 is read. But various workarounds are disabled 4314 and some IOMMU drivers will not work. 4315 bfsort Sort PCI devices into breadth-first order. 4316 This sorting is done to get a device 4317 order compatible with older (<= 2.4) kernels. 4318 nobfsort Don't sort PCI devices into breadth-first order. 4319 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 4320 tuning and use the BIOS-configured MPS defaults. 4321 pcie_bus_safe Set every device's MPS to the largest value 4322 supported by all devices below the root complex. 4323 pcie_bus_perf Set device MPS to the largest allowable MPS 4324 based on its parent bus. Also set MRRS (Max 4325 Read Request Size) to the largest supported 4326 value (no larger than the MPS that the device 4327 or bus can support) for best performance. 4328 pcie_bus_peer2peer Set every device's MPS to 128B, which 4329 every device is guaranteed to support. This 4330 configuration allows peer-to-peer DMA between 4331 any pair of devices, possibly at the cost of 4332 reduced performance. This also guarantees 4333 that hot-added devices will work. 4334 cbiosize=nn[KMG] The fixed amount of bus space which is 4335 reserved for the CardBus bridge's IO window. 4336 The default value is 256 bytes. 4337 cbmemsize=nn[KMG] The fixed amount of bus space which is 4338 reserved for the CardBus bridge's memory 4339 window. The default value is 64 megabytes. 4340 resource_alignment= 4341 Format: 4342 [<order of align>@]<pci_dev>[; ...] 4343 Specifies alignment and device to reassign 4344 aligned memory resources. How to 4345 specify the device is described above. 4346 If <order of align> is not specified, 4347 PAGE_SIZE is used as alignment. 4348 A PCI-PCI bridge can be specified if resource 4349 windows need to be expanded. 4350 To specify the alignment for several 4351 instances of a device, the PCI vendor, 4352 device, subvendor, and subdevice may be 4353 specified, e.g., 12@pci:8086:9c22:103c:198f 4354 for 4096-byte alignment. 4355 ecrc= Enable/disable PCIe ECRC (transaction layer 4356 end-to-end CRC checking). Only effective if 4357 OS has native AER control (either granted by 4358 ACPI _OSC or forced via "pcie_ports=native") 4359 bios: Use BIOS/firmware settings. This is the 4360 the default. 4361 off: Turn ECRC off 4362 on: Turn ECRC on. 4363 hpiosize=nn[KMG] The fixed amount of bus space which is 4364 reserved for hotplug bridge's IO window. 4365 Default size is 256 bytes. 4366 hpmmiosize=nn[KMG] The fixed amount of bus space which is 4367 reserved for hotplug bridge's MMIO window. 4368 Default size is 2 megabytes. 4369 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 4370 reserved for hotplug bridge's MMIO_PREF window. 4371 Default size is 2 megabytes. 4372 hpmemsize=nn[KMG] The fixed amount of bus space which is 4373 reserved for hotplug bridge's MMIO and 4374 MMIO_PREF window. 4375 Default size is 2 megabytes. 4376 hpbussize=nn The minimum amount of additional bus numbers 4377 reserved for buses below a hotplug bridge. 4378 Default is 1. 4379 realloc= Enable/disable reallocating PCI bridge resources 4380 if allocations done by BIOS are too small to 4381 accommodate resources required by all child 4382 devices. 4383 off: Turn realloc off 4384 on: Turn realloc on 4385 realloc same as realloc=on 4386 noari do not use PCIe ARI. 4387 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 4388 do not use PCIe ATS (and IOMMU device IOTLB). 4389 pcie_scan_all Scan all possible PCIe devices. Otherwise we 4390 only look for one device below a PCIe downstream 4391 port. 4392 big_root_window Try to add a big 64bit memory window to the PCIe 4393 root complex on AMD CPUs. Some GFX hardware 4394 can resize a BAR to allow access to all VRAM. 4395 Adding the window is slightly risky (it may 4396 conflict with unreported devices), so this 4397 taints the kernel. 4398 disable_acs_redir=<pci_dev>[; ...] 4399 Specify one or more PCI devices (in the format 4400 specified above) separated by semicolons. 4401 Each device specified will have the PCI ACS 4402 redirect capabilities forced off which will 4403 allow P2P traffic between devices through 4404 bridges without forcing it upstream. Note: 4405 this removes isolation between devices and 4406 may put more devices in an IOMMU group. 4407 force_floating [S390] Force usage of floating interrupts. 4408 nomio [S390] Do not use MIO instructions. 4409 norid [S390] ignore the RID field and force use of 4410 one PCI domain per PCI function 4411 4412 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 4413 Management. 4414 off Disable ASPM. 4415 force Enable ASPM even on devices that claim not to support it. 4416 WARNING: Forcing ASPM on may cause system lockups. 4417 4418 pcie_ports= [PCIE] PCIe port services handling: 4419 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 4420 even if the platform doesn't give the OS permission to 4421 use them. This may cause conflicts if the platform 4422 also tries to use these services. 4423 dpc-native Use native PCIe service for DPC only. May 4424 cause conflicts if firmware uses AER or DPC. 4425 compat Disable native PCIe services (PME, AER, DPC, PCIe 4426 hotplug). 4427 4428 pcie_port_pm= [PCIE] PCIe port power management handling: 4429 off Disable power management of all PCIe ports 4430 force Forcibly enable power management of all PCIe ports 4431 4432 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 4433 nomsi Do not use MSI for native PCIe PME signaling (this makes 4434 all PCIe root ports use INTx for all services). 4435 4436 pcmv= [HW,PCMCIA] BadgePAD 4 4437 4438 pd_ignore_unused 4439 [PM] 4440 Keep all power-domains already enabled by bootloader on, 4441 even if no driver has claimed them. This is useful 4442 for debug and development, but should not be 4443 needed on a platform with proper driver support. 4444 4445 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 4446 boot time. 4447 Format: { 0 | 1 } 4448 See arch/parisc/kernel/pdc_chassis.c 4449 4450 percpu_alloc= Select which percpu first chunk allocator to use. 4451 Currently supported values are "embed" and "page". 4452 Archs may support subset or none of the selections. 4453 See comments in mm/percpu.c for details on each 4454 allocator. This parameter is primarily for debugging 4455 and performance comparison. 4456 4457 pirq= [SMP,APIC] Manual mp-table setup 4458 See Documentation/arch/x86/i386/IO-APIC.rst. 4459 4460 plip= [PPT,NET] Parallel port network link 4461 Format: { parport<nr> | timid | 0 } 4462 See also Documentation/admin-guide/parport.rst. 4463 4464 pmtmr= [X86] Manual setup of pmtmr I/O Port. 4465 Override pmtimer IOPort with a hex value. 4466 e.g. pmtmr=0x508 4467 4468 pmu_override= [PPC] Override the PMU. 4469 This option takes over the PMU facility, so it is no 4470 longer usable by perf. Setting this option starts the 4471 PMU counters by setting MMCR0 to 0 (the FC bit is 4472 cleared). If a number is given, then MMCR1 is set to 4473 that number, otherwise (e.g., 'pmu_override=on'), MMCR1 4474 remains 0. 4475 4476 pm_debug_messages [SUSPEND,KNL] 4477 Enable suspend/resume debug messages during boot up. 4478 4479 pnp.debug=1 [PNP] 4480 Enable PNP debug messages (depends on the 4481 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 4482 via /sys/module/pnp/parameters/debug. We always show 4483 current resource usage; turning this on also shows 4484 possible settings and some assignment information. 4485 4486 pnpacpi= [ACPI] 4487 { off } 4488 4489 pnpbios= [ISAPNP] 4490 { on | off | curr | res | no-curr | no-res } 4491 4492 pnp_reserve_irq= 4493 [ISAPNP] Exclude IRQs for the autoconfiguration 4494 4495 pnp_reserve_dma= 4496 [ISAPNP] Exclude DMAs for the autoconfiguration 4497 4498 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 4499 Ranges are in pairs (I/O port base and size). 4500 4501 pnp_reserve_mem= 4502 [ISAPNP] Exclude memory regions for the 4503 autoconfiguration. 4504 Ranges are in pairs (memory base and size). 4505 4506 ports= [IP_VS_FTP] IPVS ftp helper module 4507 Default is 21. 4508 Up to 8 (IP_VS_APP_MAX_PORTS) ports 4509 may be specified. 4510 Format: <port>,<port>.... 4511 4512 powersave=off [PPC] This option disables power saving features. 4513 It specifically disables cpuidle and sets the 4514 platform machine description specific power_save 4515 function to NULL. On Idle the CPU just reduces 4516 execution priority. 4517 4518 ppc_strict_facility_enable 4519 [PPC] This option catches any kernel floating point, 4520 Altivec, VSX and SPE outside of regions specifically 4521 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 4522 There is some performance impact when enabling this. 4523 4524 ppc_tm= [PPC] 4525 Format: {"off"} 4526 Disable Hardware Transactional Memory 4527 4528 preempt= [KNL] 4529 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC 4530 none - Limited to cond_resched() calls 4531 voluntary - Limited to cond_resched() and might_sleep() calls 4532 full - Any section that isn't explicitly preempt disabled 4533 can be preempted anytime. 4534 4535 print-fatal-signals= 4536 [KNL] debug: print fatal signals 4537 4538 If enabled, warn about various signal handling 4539 related application anomalies: too many signals, 4540 too many POSIX.1 timers, fatal signals causing a 4541 coredump - etc. 4542 4543 If you hit the warning due to signal overflow, 4544 you might want to try "ulimit -i unlimited". 4545 4546 default: off. 4547 4548 printk.always_kmsg_dump= 4549 Trigger kmsg_dump for cases other than kernel oops or 4550 panics 4551 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 4552 default: disabled 4553 4554 printk.console_no_auto_verbose= 4555 Disable console loglevel raise on oops, panic 4556 or lockdep-detected issues (only if lock debug is on). 4557 With an exception to setups with low baudrate on 4558 serial console, keeping this 0 is a good choice 4559 in order to provide more debug information. 4560 Format: <bool> 4561 default: 0 (auto_verbose is enabled) 4562 4563 printk.devkmsg={on,off,ratelimit} 4564 Control writing to /dev/kmsg. 4565 on - unlimited logging to /dev/kmsg from userspace 4566 off - logging to /dev/kmsg disabled 4567 ratelimit - ratelimit the logging 4568 Default: ratelimit 4569 4570 printk.time= Show timing data prefixed to each printk message line 4571 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 4572 4573 processor.max_cstate= [HW,ACPI] 4574 Limit processor to maximum C-state 4575 max_cstate=9 overrides any DMI blacklist limit. 4576 4577 processor.nocst [HW,ACPI] 4578 Ignore the _CST method to determine C-states, 4579 instead using the legacy FADT method 4580 4581 profile= [KNL] Enable kernel profiling via /proc/profile 4582 Format: [<profiletype>,]<number> 4583 Param: <profiletype>: "schedule", "sleep", or "kvm" 4584 [defaults to kernel profiling] 4585 Param: "schedule" - profile schedule points. 4586 Param: "sleep" - profile D-state sleeping (millisecs). 4587 Requires CONFIG_SCHEDSTATS 4588 Param: "kvm" - profile VM exits. 4589 Param: <number> - step/bucket size as a power of 2 for 4590 statistical time based profiling. 4591 4592 prompt_ramdisk= [RAM] [Deprecated] 4593 4594 prot_virt= [S390] enable hosting protected virtual machines 4595 isolated from the hypervisor (if hardware supports 4596 that). 4597 Format: <bool> 4598 4599 psi= [KNL] Enable or disable pressure stall information 4600 tracking. 4601 Format: <bool> 4602 4603 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 4604 probe for; one of (bare|imps|exps|lifebook|any). 4605 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 4606 per second. 4607 psmouse.resetafter= [HW,MOUSE] 4608 Try to reset the device after so many bad packets 4609 (0 = never). 4610 psmouse.resolution= 4611 [HW,MOUSE] Set desired mouse resolution, in dpi. 4612 psmouse.smartscroll= 4613 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 4614 0 = disabled, 1 = enabled (default). 4615 4616 pstore.backend= Specify the name of the pstore backend to use 4617 4618 pti= [X86-64] Control Page Table Isolation of user and 4619 kernel address spaces. Disabling this feature 4620 removes hardening, but improves performance of 4621 system calls and interrupts. 4622 4623 on - unconditionally enable 4624 off - unconditionally disable 4625 auto - kernel detects whether your CPU model is 4626 vulnerable to issues that PTI mitigates 4627 4628 Not specifying this option is equivalent to pti=auto. 4629 4630 pty.legacy_count= 4631 [KNL] Number of legacy pty's. Overwrites compiled-in 4632 default number. 4633 4634 quiet [KNL] Disable most log messages 4635 4636 r128= [HW,DRM] 4637 4638 radix_hcall_invalidate=on [PPC/PSERIES] 4639 Disable RADIX GTSE feature and use hcall for TLB 4640 invalidate. 4641 4642 raid= [HW,RAID] 4643 See Documentation/admin-guide/md.rst. 4644 4645 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 4646 See Documentation/admin-guide/blockdev/ramdisk.rst. 4647 4648 ramdisk_start= [RAM] RAM disk image start address 4649 4650 random.trust_cpu=off 4651 [KNL] Disable trusting the use of the CPU's 4652 random number generator (if available) to 4653 initialize the kernel's RNG. 4654 4655 random.trust_bootloader=off 4656 [KNL] Disable trusting the use of the a seed 4657 passed by the bootloader (if available) to 4658 initialize the kernel's RNG. 4659 4660 randomize_kstack_offset= 4661 [KNL] Enable or disable kernel stack offset 4662 randomization, which provides roughly 5 bits of 4663 entropy, frustrating memory corruption attacks 4664 that depend on stack address determinism or 4665 cross-syscall address exposures. This is only 4666 available on architectures that have defined 4667 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET. 4668 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 4669 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT. 4670 4671 ras=option[,option,...] [KNL] RAS-specific options 4672 4673 cec_disable [X86] 4674 Disable the Correctable Errors Collector, 4675 see CONFIG_RAS_CEC help text. 4676 4677 rcu_nocbs[=cpu-list] 4678 [KNL] The optional argument is a cpu list, 4679 as described above. 4680 4681 In kernels built with CONFIG_RCU_NOCB_CPU=y, 4682 enable the no-callback CPU mode, which prevents 4683 such CPUs' callbacks from being invoked in 4684 softirq context. Invocation of such CPUs' RCU 4685 callbacks will instead be offloaded to "rcuox/N" 4686 kthreads created for that purpose, where "x" is 4687 "p" for RCU-preempt, "s" for RCU-sched, and "g" 4688 for the kthreads that mediate grace periods; and 4689 "N" is the CPU number. This reduces OS jitter on 4690 the offloaded CPUs, which can be useful for HPC 4691 and real-time workloads. It can also improve 4692 energy efficiency for asymmetric multiprocessors. 4693 4694 If a cpulist is passed as an argument, the specified 4695 list of CPUs is set to no-callback mode from boot. 4696 4697 Otherwise, if the '=' sign and the cpulist 4698 arguments are omitted, no CPU will be set to 4699 no-callback mode from boot but the mode may be 4700 toggled at runtime via cpusets. 4701 4702 Note that this argument takes precedence over 4703 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. 4704 4705 rcu_nocb_poll [KNL] 4706 Rather than requiring that offloaded CPUs 4707 (specified by rcu_nocbs= above) explicitly 4708 awaken the corresponding "rcuoN" kthreads, 4709 make these kthreads poll for callbacks. 4710 This improves the real-time response for the 4711 offloaded CPUs by relieving them of the need to 4712 wake up the corresponding kthread, but degrades 4713 energy efficiency by requiring that the kthreads 4714 periodically wake up to do the polling. 4715 4716 rcutree.blimit= [KNL] 4717 Set maximum number of finished RCU callbacks to 4718 process in one batch. 4719 4720 rcutree.dump_tree= [KNL] 4721 Dump the structure of the rcu_node combining tree 4722 out at early boot. This is used for diagnostic 4723 purposes, to verify correct tree setup. 4724 4725 rcutree.gp_cleanup_delay= [KNL] 4726 Set the number of jiffies to delay each step of 4727 RCU grace-period cleanup. 4728 4729 rcutree.gp_init_delay= [KNL] 4730 Set the number of jiffies to delay each step of 4731 RCU grace-period initialization. 4732 4733 rcutree.gp_preinit_delay= [KNL] 4734 Set the number of jiffies to delay each step of 4735 RCU grace-period pre-initialization, that is, 4736 the propagation of recent CPU-hotplug changes up 4737 the rcu_node combining tree. 4738 4739 rcutree.use_softirq= [KNL] 4740 If set to zero, move all RCU_SOFTIRQ processing to 4741 per-CPU rcuc kthreads. Defaults to a non-zero 4742 value, meaning that RCU_SOFTIRQ is used by default. 4743 Specify rcutree.use_softirq=0 to use rcuc kthreads. 4744 4745 But note that CONFIG_PREEMPT_RT=y kernels disable 4746 this kernel boot parameter, forcibly setting it 4747 to zero. 4748 4749 rcutree.rcu_fanout_exact= [KNL] 4750 Disable autobalancing of the rcu_node combining 4751 tree. This is used by rcutorture, and might 4752 possibly be useful for architectures having high 4753 cache-to-cache transfer latencies. 4754 4755 rcutree.rcu_fanout_leaf= [KNL] 4756 Change the number of CPUs assigned to each 4757 leaf rcu_node structure. Useful for very 4758 large systems, which will choose the value 64, 4759 and for NUMA systems with large remote-access 4760 latencies, which will choose a value aligned 4761 with the appropriate hardware boundaries. 4762 4763 rcutree.rcu_min_cached_objs= [KNL] 4764 Minimum number of objects which are cached and 4765 maintained per one CPU. Object size is equal 4766 to PAGE_SIZE. The cache allows to reduce the 4767 pressure to page allocator, also it makes the 4768 whole algorithm to behave better in low memory 4769 condition. 4770 4771 rcutree.rcu_delay_page_cache_fill_msec= [KNL] 4772 Set the page-cache refill delay (in milliseconds) 4773 in response to low-memory conditions. The range 4774 of permitted values is in the range 0:100000. 4775 4776 rcutree.jiffies_till_first_fqs= [KNL] 4777 Set delay from grace-period initialization to 4778 first attempt to force quiescent states. 4779 Units are jiffies, minimum value is zero, 4780 and maximum value is HZ. 4781 4782 rcutree.jiffies_till_next_fqs= [KNL] 4783 Set delay between subsequent attempts to force 4784 quiescent states. Units are jiffies, minimum 4785 value is one, and maximum value is HZ. 4786 4787 rcutree.jiffies_till_sched_qs= [KNL] 4788 Set required age in jiffies for a 4789 given grace period before RCU starts 4790 soliciting quiescent-state help from 4791 rcu_note_context_switch() and cond_resched(). 4792 If not specified, the kernel will calculate 4793 a value based on the most recent settings 4794 of rcutree.jiffies_till_first_fqs 4795 and rcutree.jiffies_till_next_fqs. 4796 This calculated value may be viewed in 4797 rcutree.jiffies_to_sched_qs. Any attempt to set 4798 rcutree.jiffies_to_sched_qs will be cheerfully 4799 overwritten. 4800 4801 rcutree.kthread_prio= [KNL,BOOT] 4802 Set the SCHED_FIFO priority of the RCU per-CPU 4803 kthreads (rcuc/N). This value is also used for 4804 the priority of the RCU boost threads (rcub/N) 4805 and for the RCU grace-period kthreads (rcu_bh, 4806 rcu_preempt, and rcu_sched). If RCU_BOOST is 4807 set, valid values are 1-99 and the default is 1 4808 (the least-favored priority). Otherwise, when 4809 RCU_BOOST is not set, valid values are 0-99 and 4810 the default is zero (non-realtime operation). 4811 When RCU_NOCB_CPU is set, also adjust the 4812 priority of NOCB callback kthreads. 4813 4814 rcutree.rcu_divisor= [KNL] 4815 Set the shift-right count to use to compute 4816 the callback-invocation batch limit bl from 4817 the number of callbacks queued on this CPU. 4818 The result will be bounded below by the value of 4819 the rcutree.blimit kernel parameter. Every bl 4820 callbacks, the softirq handler will exit in 4821 order to allow the CPU to do other work. 4822 4823 Please note that this callback-invocation batch 4824 limit applies only to non-offloaded callback 4825 invocation. Offloaded callbacks are instead 4826 invoked in the context of an rcuoc kthread, which 4827 scheduler will preempt as it does any other task. 4828 4829 rcutree.nocb_nobypass_lim_per_jiffy= [KNL] 4830 On callback-offloaded (rcu_nocbs) CPUs, 4831 RCU reduces the lock contention that would 4832 otherwise be caused by callback floods through 4833 use of the ->nocb_bypass list. However, in the 4834 common non-flooded case, RCU queues directly to 4835 the main ->cblist in order to avoid the extra 4836 overhead of the ->nocb_bypass list and its lock. 4837 But if there are too many callbacks queued during 4838 a single jiffy, RCU pre-queues the callbacks into 4839 the ->nocb_bypass queue. The definition of "too 4840 many" is supplied by this kernel boot parameter. 4841 4842 rcutree.rcu_nocb_gp_stride= [KNL] 4843 Set the number of NOCB callback kthreads in 4844 each group, which defaults to the square root 4845 of the number of CPUs. Larger numbers reduce 4846 the wakeup overhead on the global grace-period 4847 kthread, but increases that same overhead on 4848 each group's NOCB grace-period kthread. 4849 4850 rcutree.qhimark= [KNL] 4851 Set threshold of queued RCU callbacks beyond which 4852 batch limiting is disabled. 4853 4854 rcutree.qlowmark= [KNL] 4855 Set threshold of queued RCU callbacks below which 4856 batch limiting is re-enabled. 4857 4858 rcutree.qovld= [KNL] 4859 Set threshold of queued RCU callbacks beyond which 4860 RCU's force-quiescent-state scan will aggressively 4861 enlist help from cond_resched() and sched IPIs to 4862 help CPUs more quickly reach quiescent states. 4863 Set to less than zero to make this be set based 4864 on rcutree.qhimark at boot time and to zero to 4865 disable more aggressive help enlistment. 4866 4867 rcutree.rcu_kick_kthreads= [KNL] 4868 Cause the grace-period kthread to get an extra 4869 wake_up() if it sleeps three times longer than 4870 it should at force-quiescent-state time. 4871 This wake_up() will be accompanied by a 4872 WARN_ONCE() splat and an ftrace_dump(). 4873 4874 rcutree.rcu_unlock_delay= [KNL] 4875 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, 4876 this specifies an rcu_read_unlock()-time delay 4877 in microseconds. This defaults to zero. 4878 Larger delays increase the probability of 4879 catching RCU pointer leaks, that is, buggy use 4880 of RCU-protected pointers after the relevant 4881 rcu_read_unlock() has completed. 4882 4883 rcutree.sysrq_rcu= [KNL] 4884 Commandeer a sysrq key to dump out Tree RCU's 4885 rcu_node tree with an eye towards determining 4886 why a new grace period has not yet started. 4887 4888 rcuscale.gp_async= [KNL] 4889 Measure performance of asynchronous 4890 grace-period primitives such as call_rcu(). 4891 4892 rcuscale.gp_async_max= [KNL] 4893 Specify the maximum number of outstanding 4894 callbacks per writer thread. When a writer 4895 thread exceeds this limit, it invokes the 4896 corresponding flavor of rcu_barrier() to allow 4897 previously posted callbacks to drain. 4898 4899 rcuscale.gp_exp= [KNL] 4900 Measure performance of expedited synchronous 4901 grace-period primitives. 4902 4903 rcuscale.holdoff= [KNL] 4904 Set test-start holdoff period. The purpose of 4905 this parameter is to delay the start of the 4906 test until boot completes in order to avoid 4907 interference. 4908 4909 rcuscale.kfree_rcu_test= [KNL] 4910 Set to measure performance of kfree_rcu() flooding. 4911 4912 rcuscale.kfree_rcu_test_double= [KNL] 4913 Test the double-argument variant of kfree_rcu(). 4914 If this parameter has the same value as 4915 rcuscale.kfree_rcu_test_single, both the single- 4916 and double-argument variants are tested. 4917 4918 rcuscale.kfree_rcu_test_single= [KNL] 4919 Test the single-argument variant of kfree_rcu(). 4920 If this parameter has the same value as 4921 rcuscale.kfree_rcu_test_double, both the single- 4922 and double-argument variants are tested. 4923 4924 rcuscale.kfree_nthreads= [KNL] 4925 The number of threads running loops of kfree_rcu(). 4926 4927 rcuscale.kfree_alloc_num= [KNL] 4928 Number of allocations and frees done in an iteration. 4929 4930 rcuscale.kfree_loops= [KNL] 4931 Number of loops doing rcuscale.kfree_alloc_num number 4932 of allocations and frees. 4933 4934 rcuscale.nreaders= [KNL] 4935 Set number of RCU readers. The value -1 selects 4936 N, where N is the number of CPUs. A value 4937 "n" less than -1 selects N-n+1, where N is again 4938 the number of CPUs. For example, -2 selects N 4939 (the number of CPUs), -3 selects N+1, and so on. 4940 A value of "n" less than or equal to -N selects 4941 a single reader. 4942 4943 rcuscale.nwriters= [KNL] 4944 Set number of RCU writers. The values operate 4945 the same as for rcuscale.nreaders. 4946 N, where N is the number of CPUs 4947 4948 rcuscale.perf_type= [KNL] 4949 Specify the RCU implementation to test. 4950 4951 rcuscale.shutdown= [KNL] 4952 Shut the system down after performance tests 4953 complete. This is useful for hands-off automated 4954 testing. 4955 4956 rcuscale.verbose= [KNL] 4957 Enable additional printk() statements. 4958 4959 rcuscale.writer_holdoff= [KNL] 4960 Write-side holdoff between grace periods, 4961 in microseconds. The default of zero says 4962 no holdoff. 4963 4964 rcutorture.fqs_duration= [KNL] 4965 Set duration of force_quiescent_state bursts 4966 in microseconds. 4967 4968 rcutorture.fqs_holdoff= [KNL] 4969 Set holdoff time within force_quiescent_state bursts 4970 in microseconds. 4971 4972 rcutorture.fqs_stutter= [KNL] 4973 Set wait time between force_quiescent_state bursts 4974 in seconds. 4975 4976 rcutorture.fwd_progress= [KNL] 4977 Specifies the number of kthreads to be used 4978 for RCU grace-period forward-progress testing 4979 for the types of RCU supporting this notion. 4980 Defaults to 1 kthread, values less than zero or 4981 greater than the number of CPUs cause the number 4982 of CPUs to be used. 4983 4984 rcutorture.fwd_progress_div= [KNL] 4985 Specify the fraction of a CPU-stall-warning 4986 period to do tight-loop forward-progress testing. 4987 4988 rcutorture.fwd_progress_holdoff= [KNL] 4989 Number of seconds to wait between successive 4990 forward-progress tests. 4991 4992 rcutorture.fwd_progress_need_resched= [KNL] 4993 Enclose cond_resched() calls within checks for 4994 need_resched() during tight-loop forward-progress 4995 testing. 4996 4997 rcutorture.gp_cond= [KNL] 4998 Use conditional/asynchronous update-side 4999 primitives, if available. 5000 5001 rcutorture.gp_exp= [KNL] 5002 Use expedited update-side primitives, if available. 5003 5004 rcutorture.gp_normal= [KNL] 5005 Use normal (non-expedited) asynchronous 5006 update-side primitives, if available. 5007 5008 rcutorture.gp_sync= [KNL] 5009 Use normal (non-expedited) synchronous 5010 update-side primitives, if available. If all 5011 of rcutorture.gp_cond=, rcutorture.gp_exp=, 5012 rcutorture.gp_normal=, and rcutorture.gp_sync= 5013 are zero, rcutorture acts as if is interpreted 5014 they are all non-zero. 5015 5016 rcutorture.irqreader= [KNL] 5017 Run RCU readers from irq handlers, or, more 5018 accurately, from a timer handler. Not all RCU 5019 flavors take kindly to this sort of thing. 5020 5021 rcutorture.leakpointer= [KNL] 5022 Leak an RCU-protected pointer out of the reader. 5023 This can of course result in splats, and is 5024 intended to test the ability of things like 5025 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect 5026 such leaks. 5027 5028 rcutorture.n_barrier_cbs= [KNL] 5029 Set callbacks/threads for rcu_barrier() testing. 5030 5031 rcutorture.nfakewriters= [KNL] 5032 Set number of concurrent RCU writers. These just 5033 stress RCU, they don't participate in the actual 5034 test, hence the "fake". 5035 5036 rcutorture.nocbs_nthreads= [KNL] 5037 Set number of RCU callback-offload togglers. 5038 Zero (the default) disables toggling. 5039 5040 rcutorture.nocbs_toggle= [KNL] 5041 Set the delay in milliseconds between successive 5042 callback-offload toggling attempts. 5043 5044 rcutorture.nreaders= [KNL] 5045 Set number of RCU readers. The value -1 selects 5046 N-1, where N is the number of CPUs. A value 5047 "n" less than -1 selects N-n-2, where N is again 5048 the number of CPUs. For example, -2 selects N 5049 (the number of CPUs), -3 selects N+1, and so on. 5050 5051 rcutorture.object_debug= [KNL] 5052 Enable debug-object double-call_rcu() testing. 5053 5054 rcutorture.onoff_holdoff= [KNL] 5055 Set time (s) after boot for CPU-hotplug testing. 5056 5057 rcutorture.onoff_interval= [KNL] 5058 Set time (jiffies) between CPU-hotplug operations, 5059 or zero to disable CPU-hotplug testing. 5060 5061 rcutorture.read_exit= [KNL] 5062 Set the number of read-then-exit kthreads used 5063 to test the interaction of RCU updaters and 5064 task-exit processing. 5065 5066 rcutorture.read_exit_burst= [KNL] 5067 The number of times in a given read-then-exit 5068 episode that a set of read-then-exit kthreads 5069 is spawned. 5070 5071 rcutorture.read_exit_delay= [KNL] 5072 The delay, in seconds, between successive 5073 read-then-exit testing episodes. 5074 5075 rcutorture.shuffle_interval= [KNL] 5076 Set task-shuffle interval (s). Shuffling tasks 5077 allows some CPUs to go into dyntick-idle mode 5078 during the rcutorture test. 5079 5080 rcutorture.shutdown_secs= [KNL] 5081 Set time (s) after boot system shutdown. This 5082 is useful for hands-off automated testing. 5083 5084 rcutorture.stall_cpu= [KNL] 5085 Duration of CPU stall (s) to test RCU CPU stall 5086 warnings, zero to disable. 5087 5088 rcutorture.stall_cpu_block= [KNL] 5089 Sleep while stalling if set. This will result 5090 in warnings from preemptible RCU in addition 5091 to any other stall-related activity. 5092 5093 rcutorture.stall_cpu_holdoff= [KNL] 5094 Time to wait (s) after boot before inducing stall. 5095 5096 rcutorture.stall_cpu_irqsoff= [KNL] 5097 Disable interrupts while stalling if set. 5098 5099 rcutorture.stall_gp_kthread= [KNL] 5100 Duration (s) of forced sleep within RCU 5101 grace-period kthread to test RCU CPU stall 5102 warnings, zero to disable. If both stall_cpu 5103 and stall_gp_kthread are specified, the 5104 kthread is starved first, then the CPU. 5105 5106 rcutorture.stat_interval= [KNL] 5107 Time (s) between statistics printk()s. 5108 5109 rcutorture.stutter= [KNL] 5110 Time (s) to stutter testing, for example, specifying 5111 five seconds causes the test to run for five seconds, 5112 wait for five seconds, and so on. This tests RCU's 5113 ability to transition abruptly to and from idle. 5114 5115 rcutorture.test_boost= [KNL] 5116 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 5117 "Maybe" means test if the RCU implementation 5118 under test support RCU priority boosting. 5119 5120 rcutorture.test_boost_duration= [KNL] 5121 Duration (s) of each individual boost test. 5122 5123 rcutorture.test_boost_interval= [KNL] 5124 Interval (s) between each boost test. 5125 5126 rcutorture.test_no_idle_hz= [KNL] 5127 Test RCU's dyntick-idle handling. See also the 5128 rcutorture.shuffle_interval parameter. 5129 5130 rcutorture.torture_type= [KNL] 5131 Specify the RCU implementation to test. 5132 5133 rcutorture.verbose= [KNL] 5134 Enable additional printk() statements. 5135 5136 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 5137 Dump ftrace buffer after reporting RCU CPU 5138 stall warning. 5139 5140 rcupdate.rcu_cpu_stall_suppress= [KNL] 5141 Suppress RCU CPU stall warning messages. 5142 5143 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 5144 Suppress RCU CPU stall warning messages and 5145 rcutorture writer stall warnings that occur 5146 during early boot, that is, during the time 5147 before the init task is spawned. 5148 5149 rcupdate.rcu_cpu_stall_timeout= [KNL] 5150 Set timeout for RCU CPU stall warning messages. 5151 The value is in seconds and the maximum allowed 5152 value is 300 seconds. 5153 5154 rcupdate.rcu_exp_cpu_stall_timeout= [KNL] 5155 Set timeout for expedited RCU CPU stall warning 5156 messages. The value is in milliseconds 5157 and the maximum allowed value is 21000 5158 milliseconds. Please note that this value is 5159 adjusted to an arch timer tick resolution. 5160 Setting this to zero causes the value from 5161 rcupdate.rcu_cpu_stall_timeout to be used (after 5162 conversion from seconds to milliseconds). 5163 5164 rcupdate.rcu_cpu_stall_cputime= [KNL] 5165 Provide statistics on the cputime and count of 5166 interrupts and tasks during the sampling period. For 5167 multiple continuous RCU stalls, all sampling periods 5168 begin at half of the first RCU stall timeout. 5169 5170 rcupdate.rcu_exp_stall_task_details= [KNL] 5171 Print stack dumps of any tasks blocking the 5172 current expedited RCU grace period during an 5173 expedited RCU CPU stall warning. 5174 5175 rcupdate.rcu_expedited= [KNL] 5176 Use expedited grace-period primitives, for 5177 example, synchronize_rcu_expedited() instead 5178 of synchronize_rcu(). This reduces latency, 5179 but can increase CPU utilization, degrade 5180 real-time latency, and degrade energy efficiency. 5181 No effect on CONFIG_TINY_RCU kernels. 5182 5183 rcupdate.rcu_normal= [KNL] 5184 Use only normal grace-period primitives, 5185 for example, synchronize_rcu() instead of 5186 synchronize_rcu_expedited(). This improves 5187 real-time latency, CPU utilization, and 5188 energy efficiency, but can expose users to 5189 increased grace-period latency. This parameter 5190 overrides rcupdate.rcu_expedited. No effect on 5191 CONFIG_TINY_RCU kernels. 5192 5193 rcupdate.rcu_normal_after_boot= [KNL] 5194 Once boot has completed (that is, after 5195 rcu_end_inkernel_boot() has been invoked), use 5196 only normal grace-period primitives. No effect 5197 on CONFIG_TINY_RCU kernels. 5198 5199 But note that CONFIG_PREEMPT_RT=y kernels enables 5200 this kernel boot parameter, forcibly setting 5201 it to the value one, that is, converting any 5202 post-boot attempt at an expedited RCU grace 5203 period to instead use normal non-expedited 5204 grace-period processing. 5205 5206 rcupdate.rcu_task_collapse_lim= [KNL] 5207 Set the maximum number of callbacks present 5208 at the beginning of a grace period that allows 5209 the RCU Tasks flavors to collapse back to using 5210 a single callback queue. This switching only 5211 occurs when rcupdate.rcu_task_enqueue_lim is 5212 set to the default value of -1. 5213 5214 rcupdate.rcu_task_contend_lim= [KNL] 5215 Set the minimum number of callback-queuing-time 5216 lock-contention events per jiffy required to 5217 cause the RCU Tasks flavors to switch to per-CPU 5218 callback queuing. This switching only occurs 5219 when rcupdate.rcu_task_enqueue_lim is set to 5220 the default value of -1. 5221 5222 rcupdate.rcu_task_enqueue_lim= [KNL] 5223 Set the number of callback queues to use for the 5224 RCU Tasks family of RCU flavors. The default 5225 of -1 allows this to be automatically (and 5226 dynamically) adjusted. This parameter is intended 5227 for use in testing. 5228 5229 rcupdate.rcu_task_ipi_delay= [KNL] 5230 Set time in jiffies during which RCU tasks will 5231 avoid sending IPIs, starting with the beginning 5232 of a given grace period. Setting a large 5233 number avoids disturbing real-time workloads, 5234 but lengthens grace periods. 5235 5236 rcupdate.rcu_task_stall_info= [KNL] 5237 Set initial timeout in jiffies for RCU task stall 5238 informational messages, which give some indication 5239 of the problem for those not patient enough to 5240 wait for ten minutes. Informational messages are 5241 only printed prior to the stall-warning message 5242 for a given grace period. Disable with a value 5243 less than or equal to zero. Defaults to ten 5244 seconds. A change in value does not take effect 5245 until the beginning of the next grace period. 5246 5247 rcupdate.rcu_task_stall_info_mult= [KNL] 5248 Multiplier for time interval between successive 5249 RCU task stall informational messages for a given 5250 RCU tasks grace period. This value is clamped 5251 to one through ten, inclusive. It defaults to 5252 the value three, so that the first informational 5253 message is printed 10 seconds into the grace 5254 period, the second at 40 seconds, the third at 5255 160 seconds, and then the stall warning at 600 5256 seconds would prevent a fourth at 640 seconds. 5257 5258 rcupdate.rcu_task_stall_timeout= [KNL] 5259 Set timeout in jiffies for RCU task stall 5260 warning messages. Disable with a value less 5261 than or equal to zero. Defaults to ten minutes. 5262 A change in value does not take effect until 5263 the beginning of the next grace period. 5264 5265 rcupdate.rcu_self_test= [KNL] 5266 Run the RCU early boot self tests 5267 5268 rdinit= [KNL] 5269 Format: <full_path> 5270 Run specified binary instead of /init from the ramdisk, 5271 used for early userspace startup. See initrd. 5272 5273 rdrand= [X86] 5274 force - Override the decision by the kernel to hide the 5275 advertisement of RDRAND support (this affects 5276 certain AMD processors because of buggy BIOS 5277 support, specifically around the suspend/resume 5278 path). 5279 5280 rdt= [HW,X86,RDT] 5281 Turn on/off individual RDT features. List is: 5282 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 5283 mba, smba, bmec. 5284 E.g. to turn on cmt and turn off mba use: 5285 rdt=cmt,!mba 5286 5287 reboot= [KNL] 5288 Format (x86 or x86_64): 5289 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] | d[efault] \ 5290 [[,]s[mp]#### \ 5291 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 5292 [[,]f[orce] 5293 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 5294 (prefix with 'panic_' to set mode for panic 5295 reboot only), 5296 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 5297 reboot_force is either force or not specified, 5298 reboot_cpu is s[mp]#### with #### being the processor 5299 to be used for rebooting. 5300 5301 refscale.holdoff= [KNL] 5302 Set test-start holdoff period. The purpose of 5303 this parameter is to delay the start of the 5304 test until boot completes in order to avoid 5305 interference. 5306 5307 refscale.loops= [KNL] 5308 Set the number of loops over the synchronization 5309 primitive under test. Increasing this number 5310 reduces noise due to loop start/end overhead, 5311 but the default has already reduced the per-pass 5312 noise to a handful of picoseconds on ca. 2020 5313 x86 laptops. 5314 5315 refscale.nreaders= [KNL] 5316 Set number of readers. The default value of -1 5317 selects N, where N is roughly 75% of the number 5318 of CPUs. A value of zero is an interesting choice. 5319 5320 refscale.nruns= [KNL] 5321 Set number of runs, each of which is dumped onto 5322 the console log. 5323 5324 refscale.readdelay= [KNL] 5325 Set the read-side critical-section duration, 5326 measured in microseconds. 5327 5328 refscale.scale_type= [KNL] 5329 Specify the read-protection implementation to test. 5330 5331 refscale.shutdown= [KNL] 5332 Shut down the system at the end of the performance 5333 test. This defaults to 1 (shut it down) when 5334 refscale is built into the kernel and to 0 (leave 5335 it running) when refscale is built as a module. 5336 5337 refscale.verbose= [KNL] 5338 Enable additional printk() statements. 5339 5340 refscale.verbose_batched= [KNL] 5341 Batch the additional printk() statements. If zero 5342 (the default) or negative, print everything. Otherwise, 5343 print every Nth verbose statement, where N is the value 5344 specified. 5345 5346 relax_domain_level= 5347 [KNL, SMP] Set scheduler's default relax_domain_level. 5348 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 5349 5350 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 5351 Format: <base1>,<size1>[,<base2>,<size2>,...] 5352 Reserve I/O ports or memory so the kernel won't use 5353 them. If <base> is less than 0x10000, the region 5354 is assumed to be I/O ports; otherwise it is memory. 5355 5356 reservetop= [X86-32] 5357 Format: nn[KMG] 5358 Reserves a hole at the top of the kernel virtual 5359 address space. 5360 5361 reset_devices [KNL] Force drivers to reset the underlying device 5362 during initialization. 5363 5364 resume= [SWSUSP] 5365 Specify the partition device for software suspend 5366 Format: 5367 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 5368 5369 resume_offset= [SWSUSP] 5370 Specify the offset from the beginning of the partition 5371 given by "resume=" at which the swap header is located, 5372 in <PAGE_SIZE> units (needed only for swap files). 5373 See Documentation/power/swsusp-and-swap-files.rst 5374 5375 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 5376 read the resume files 5377 5378 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 5379 Useful for devices that are detected asynchronously 5380 (e.g. USB and MMC devices). 5381 5382 retain_initrd [RAM] Keep initrd memory after extraction 5383 5384 retbleed= [X86] Control mitigation of RETBleed (Arbitrary 5385 Speculative Code Execution with Return Instructions) 5386 vulnerability. 5387 5388 AMD-based UNRET and IBPB mitigations alone do not stop 5389 sibling threads from influencing the predictions of other 5390 sibling threads. For that reason, STIBP is used on pro- 5391 cessors that support it, and mitigate SMT on processors 5392 that don't. 5393 5394 off - no mitigation 5395 auto - automatically select a migitation 5396 auto,nosmt - automatically select a mitigation, 5397 disabling SMT if necessary for 5398 the full mitigation (only on Zen1 5399 and older without STIBP). 5400 ibpb - On AMD, mitigate short speculation 5401 windows on basic block boundaries too. 5402 Safe, highest perf impact. It also 5403 enables STIBP if present. Not suitable 5404 on Intel. 5405 ibpb,nosmt - Like "ibpb" above but will disable SMT 5406 when STIBP is not available. This is 5407 the alternative for systems which do not 5408 have STIBP. 5409 unret - Force enable untrained return thunks, 5410 only effective on AMD f15h-f17h based 5411 systems. 5412 unret,nosmt - Like unret, but will disable SMT when STIBP 5413 is not available. This is the alternative for 5414 systems which do not have STIBP. 5415 5416 Selecting 'auto' will choose a mitigation method at run 5417 time according to the CPU. 5418 5419 Not specifying this option is equivalent to retbleed=auto. 5420 5421 rfkill.default_state= 5422 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 5423 etc. communication is blocked by default. 5424 1 Unblocked. 5425 5426 rfkill.master_switch_mode= 5427 0 The "airplane mode" button does nothing. 5428 1 The "airplane mode" button toggles between everything 5429 blocked and the previous configuration. 5430 2 The "airplane mode" button toggles between everything 5431 blocked and everything unblocked. 5432 5433 rhash_entries= [KNL,NET] 5434 Set number of hash buckets for route cache 5435 5436 ring3mwait=disable 5437 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 5438 CPUs. 5439 5440 ro [KNL] Mount root device read-only on boot 5441 5442 rodata= [KNL] 5443 on Mark read-only kernel memory as read-only (default). 5444 off Leave read-only kernel memory writable for debugging. 5445 full Mark read-only kernel memory and aliases as read-only 5446 [arm64] 5447 5448 rockchip.usb_uart 5449 Enable the uart passthrough on the designated usb port 5450 on Rockchip SoCs. When active, the signals of the 5451 debug-uart get routed to the D+ and D- pins of the usb 5452 port and the regular usb controller gets disabled. 5453 5454 root= [KNL] Root filesystem 5455 See name_to_dev_t comment in init/do_mounts.c. 5456 5457 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 5458 mount the root filesystem 5459 5460 rootflags= [KNL] Set root filesystem mount option string 5461 5462 rootfstype= [KNL] Set root filesystem type 5463 5464 rootwait [KNL] Wait (indefinitely) for root device to show up. 5465 Useful for devices that are detected asynchronously 5466 (e.g. USB and MMC devices). 5467 5468 rproc_mem=nn[KMG][@address] 5469 [KNL,ARM,CMA] Remoteproc physical memory block. 5470 Memory area to be used by remote processor image, 5471 managed by CMA. 5472 5473 rw [KNL] Mount root device read-write on boot 5474 5475 S [KNL] Run init in single mode 5476 5477 s390_iommu= [HW,S390] 5478 Set s390 IOTLB flushing mode 5479 strict 5480 With strict flushing every unmap operation will result in 5481 an IOTLB flush. Default is lazy flushing before reuse, 5482 which is faster. 5483 5484 s390_iommu_aperture= [KNL,S390] 5485 Specifies the size of the per device DMA address space 5486 accessible through the DMA and IOMMU APIs as a decimal 5487 factor of the size of main memory. 5488 The default is 1 meaning that one can concurrently use 5489 as many DMA addresses as physical memory is installed, 5490 if supported by hardware, and thus map all of memory 5491 once. With a value of 2 one can map all of memory twice 5492 and so on. As a special case a factor of 0 imposes no 5493 restrictions other than those given by hardware at the 5494 cost of significant additional memory use for tables. 5495 5496 sa1100ir [NET] 5497 See drivers/net/irda/sa1100_ir.c. 5498 5499 sched_verbose [KNL] Enables verbose scheduler debug messages. 5500 5501 schedstats= [KNL,X86] Enable or disable scheduled statistics. 5502 Allowed values are enable and disable. This feature 5503 incurs a small amount of overhead in the scheduler 5504 but is useful for debugging and performance tuning. 5505 5506 sched_thermal_decay_shift= 5507 [KNL, SMP] Set a decay shift for scheduler thermal 5508 pressure signal. Thermal pressure signal follows the 5509 default decay period of other scheduler pelt 5510 signals(usually 32 ms but configurable). Setting 5511 sched_thermal_decay_shift will left shift the decay 5512 period for the thermal pressure signal by the shift 5513 value. 5514 i.e. with the default pelt decay period of 32 ms 5515 sched_thermal_decay_shift thermal pressure decay pr 5516 1 64 ms 5517 2 128 ms 5518 and so on. 5519 Format: integer between 0 and 10 5520 Default is 0. 5521 5522 scftorture.holdoff= [KNL] 5523 Number of seconds to hold off before starting 5524 test. Defaults to zero for module insertion and 5525 to 10 seconds for built-in smp_call_function() 5526 tests. 5527 5528 scftorture.longwait= [KNL] 5529 Request ridiculously long waits randomly selected 5530 up to the chosen limit in seconds. Zero (the 5531 default) disables this feature. Please note 5532 that requesting even small non-zero numbers of 5533 seconds can result in RCU CPU stall warnings, 5534 softlockup complaints, and so on. 5535 5536 scftorture.nthreads= [KNL] 5537 Number of kthreads to spawn to invoke the 5538 smp_call_function() family of functions. 5539 The default of -1 specifies a number of kthreads 5540 equal to the number of CPUs. 5541 5542 scftorture.onoff_holdoff= [KNL] 5543 Number seconds to wait after the start of the 5544 test before initiating CPU-hotplug operations. 5545 5546 scftorture.onoff_interval= [KNL] 5547 Number seconds to wait between successive 5548 CPU-hotplug operations. Specifying zero (which 5549 is the default) disables CPU-hotplug operations. 5550 5551 scftorture.shutdown_secs= [KNL] 5552 The number of seconds following the start of the 5553 test after which to shut down the system. The 5554 default of zero avoids shutting down the system. 5555 Non-zero values are useful for automated tests. 5556 5557 scftorture.stat_interval= [KNL] 5558 The number of seconds between outputting the 5559 current test statistics to the console. A value 5560 of zero disables statistics output. 5561 5562 scftorture.stutter_cpus= [KNL] 5563 The number of jiffies to wait between each change 5564 to the set of CPUs under test. 5565 5566 scftorture.use_cpus_read_lock= [KNL] 5567 Use use_cpus_read_lock() instead of the default 5568 preempt_disable() to disable CPU hotplug 5569 while invoking one of the smp_call_function*() 5570 functions. 5571 5572 scftorture.verbose= [KNL] 5573 Enable additional printk() statements. 5574 5575 scftorture.weight_single= [KNL] 5576 The probability weighting to use for the 5577 smp_call_function_single() function with a zero 5578 "wait" parameter. A value of -1 selects the 5579 default if all other weights are -1. However, 5580 if at least one weight has some other value, a 5581 value of -1 will instead select a weight of zero. 5582 5583 scftorture.weight_single_wait= [KNL] 5584 The probability weighting to use for the 5585 smp_call_function_single() function with a 5586 non-zero "wait" parameter. See weight_single. 5587 5588 scftorture.weight_many= [KNL] 5589 The probability weighting to use for the 5590 smp_call_function_many() function with a zero 5591 "wait" parameter. See weight_single. 5592 Note well that setting a high probability for 5593 this weighting can place serious IPI load 5594 on the system. 5595 5596 scftorture.weight_many_wait= [KNL] 5597 The probability weighting to use for the 5598 smp_call_function_many() function with a 5599 non-zero "wait" parameter. See weight_single 5600 and weight_many. 5601 5602 scftorture.weight_all= [KNL] 5603 The probability weighting to use for the 5604 smp_call_function_all() function with a zero 5605 "wait" parameter. See weight_single and 5606 weight_many. 5607 5608 scftorture.weight_all_wait= [KNL] 5609 The probability weighting to use for the 5610 smp_call_function_all() function with a 5611 non-zero "wait" parameter. See weight_single 5612 and weight_many. 5613 5614 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 5615 xtime_lock contention on larger systems, and/or RCU lock 5616 contention on all systems with CONFIG_MAXSMP set. 5617 Format: { "0" | "1" } 5618 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 5619 1 -- enable. 5620 Note: increases power consumption, thus should only be 5621 enabled if running jitter sensitive (HPC/RT) workloads. 5622 5623 security= [SECURITY] Choose a legacy "major" security module to 5624 enable at boot. This has been deprecated by the 5625 "lsm=" parameter. 5626 5627 selinux= [SELINUX] Disable or enable SELinux at boot time. 5628 Format: { "0" | "1" } 5629 See security/selinux/Kconfig help text. 5630 0 -- disable. 5631 1 -- enable. 5632 Default value is 1. 5633 5634 serialnumber [BUGS=X86-32] 5635 5636 sev=option[,option...] [X86-64] See Documentation/arch/x86/x86_64/boot-options.rst 5637 5638 shapers= [NET] 5639 Maximal number of shapers. 5640 5641 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 5642 Limit apic dumping. The parameter defines the maximal 5643 number of local apics being dumped. Also it is possible 5644 to set it to "all" by meaning -- no limit here. 5645 Format: { 1 (default) | 2 | ... | all }. 5646 The parameter valid if only apic=debug or 5647 apic=verbose is specified. 5648 Example: apic=debug show_lapic=all 5649 5650 simeth= [IA-64] 5651 simscsi= 5652 5653 slram= [HW,MTD] 5654 5655 slab_merge [MM] 5656 Enable merging of slabs with similar size when the 5657 kernel is built without CONFIG_SLAB_MERGE_DEFAULT. 5658 5659 slab_nomerge [MM] 5660 Disable merging of slabs with similar size. May be 5661 necessary if there is some reason to distinguish 5662 allocs to different slabs, especially in hardened 5663 environments where the risk of heap overflows and 5664 layout control by attackers can usually be 5665 frustrated by disabling merging. This will reduce 5666 most of the exposure of a heap attack to a single 5667 cache (risks via metadata attacks are mostly 5668 unchanged). Debug options disable merging on their 5669 own. 5670 For more information see Documentation/mm/slub.rst. 5671 5672 slab_max_order= [MM, SLAB] 5673 Determines the maximum allowed order for slabs. 5674 A high setting may cause OOMs due to memory 5675 fragmentation. Defaults to 1 for systems with 5676 more than 32MB of RAM, 0 otherwise. 5677 5678 slub_debug[=options[,slabs][;[options[,slabs]]...] [MM, SLUB] 5679 Enabling slub_debug allows one to determine the 5680 culprit if slab objects become corrupted. Enabling 5681 slub_debug can create guard zones around objects and 5682 may poison objects when not in use. Also tracks the 5683 last alloc / free. For more information see 5684 Documentation/mm/slub.rst. 5685 5686 slub_max_order= [MM, SLUB] 5687 Determines the maximum allowed order for slabs. 5688 A high setting may cause OOMs due to memory 5689 fragmentation. For more information see 5690 Documentation/mm/slub.rst. 5691 5692 slub_min_objects= [MM, SLUB] 5693 The minimum number of objects per slab. SLUB will 5694 increase the slab order up to slub_max_order to 5695 generate a sufficiently large slab able to contain 5696 the number of objects indicated. The higher the number 5697 of objects the smaller the overhead of tracking slabs 5698 and the less frequently locks need to be acquired. 5699 For more information see Documentation/mm/slub.rst. 5700 5701 slub_min_order= [MM, SLUB] 5702 Determines the minimum page order for slabs. Must be 5703 lower than slub_max_order. 5704 For more information see Documentation/mm/slub.rst. 5705 5706 slub_merge [MM, SLUB] 5707 Same with slab_merge. 5708 5709 slub_nomerge [MM, SLUB] 5710 Same with slab_nomerge. This is supported for legacy. 5711 See slab_nomerge for more information. 5712 5713 smart2= [HW] 5714 Format: <io1>[,<io2>[,...,<io8>]] 5715 5716 smp.csd_lock_timeout= [KNL] 5717 Specify the period of time in milliseconds 5718 that smp_call_function() and friends will wait 5719 for a CPU to release the CSD lock. This is 5720 useful when diagnosing bugs involving CPUs 5721 disabling interrupts for extended periods 5722 of time. Defaults to 5,000 milliseconds, and 5723 setting a value of zero disables this feature. 5724 This feature may be more efficiently disabled 5725 using the csdlock_debug- kernel parameter. 5726 5727 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 5728 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 5729 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 5730 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 5731 smsc-ircc2.ircc_irq= [HW] IRQ line 5732 smsc-ircc2.ircc_dma= [HW] DMA channel 5733 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 5734 0: Toshiba Satellite 1800 (GP data pin select) 5735 1: Fast pin select (default) 5736 2: ATC IRMode 5737 5738 smt= [KNL,S390] Set the maximum number of threads (logical 5739 CPUs) to use per physical CPU on systems capable of 5740 symmetric multithreading (SMT). Will be capped to the 5741 actual hardware limit. 5742 Format: <integer> 5743 Default: -1 (no limit) 5744 5745 softlockup_panic= 5746 [KNL] Should the soft-lockup detector generate panics. 5747 Format: 0 | 1 5748 5749 A value of 1 instructs the soft-lockup detector 5750 to panic the machine when a soft-lockup occurs. It is 5751 also controlled by the kernel.softlockup_panic sysctl 5752 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 5753 respective build-time switch to that functionality. 5754 5755 softlockup_all_cpu_backtrace= 5756 [KNL] Should the soft-lockup detector generate 5757 backtraces on all cpus. 5758 Format: 0 | 1 5759 5760 sonypi.*= [HW] Sony Programmable I/O Control Device driver 5761 See Documentation/admin-guide/laptops/sonypi.rst 5762 5763 spectre_v2= [X86] Control mitigation of Spectre variant 2 5764 (indirect branch speculation) vulnerability. 5765 The default operation protects the kernel from 5766 user space attacks. 5767 5768 on - unconditionally enable, implies 5769 spectre_v2_user=on 5770 off - unconditionally disable, implies 5771 spectre_v2_user=off 5772 auto - kernel detects whether your CPU model is 5773 vulnerable 5774 5775 Selecting 'on' will, and 'auto' may, choose a 5776 mitigation method at run time according to the 5777 CPU, the available microcode, the setting of the 5778 CONFIG_RETPOLINE configuration option, and the 5779 compiler with which the kernel was built. 5780 5781 Selecting 'on' will also enable the mitigation 5782 against user space to user space task attacks. 5783 5784 Selecting 'off' will disable both the kernel and 5785 the user space protections. 5786 5787 Specific mitigations can also be selected manually: 5788 5789 retpoline - replace indirect branches 5790 retpoline,generic - Retpolines 5791 retpoline,lfence - LFENCE; indirect branch 5792 retpoline,amd - alias for retpoline,lfence 5793 eibrs - Enhanced/Auto IBRS 5794 eibrs,retpoline - Enhanced/Auto IBRS + Retpolines 5795 eibrs,lfence - Enhanced/Auto IBRS + LFENCE 5796 ibrs - use IBRS to protect kernel 5797 5798 Not specifying this option is equivalent to 5799 spectre_v2=auto. 5800 5801 spectre_v2_user= 5802 [X86] Control mitigation of Spectre variant 2 5803 (indirect branch speculation) vulnerability between 5804 user space tasks 5805 5806 on - Unconditionally enable mitigations. Is 5807 enforced by spectre_v2=on 5808 5809 off - Unconditionally disable mitigations. Is 5810 enforced by spectre_v2=off 5811 5812 prctl - Indirect branch speculation is enabled, 5813 but mitigation can be enabled via prctl 5814 per thread. The mitigation control state 5815 is inherited on fork. 5816 5817 prctl,ibpb 5818 - Like "prctl" above, but only STIBP is 5819 controlled per thread. IBPB is issued 5820 always when switching between different user 5821 space processes. 5822 5823 seccomp 5824 - Same as "prctl" above, but all seccomp 5825 threads will enable the mitigation unless 5826 they explicitly opt out. 5827 5828 seccomp,ibpb 5829 - Like "seccomp" above, but only STIBP is 5830 controlled per thread. IBPB is issued 5831 always when switching between different 5832 user space processes. 5833 5834 auto - Kernel selects the mitigation depending on 5835 the available CPU features and vulnerability. 5836 5837 Default mitigation: "prctl" 5838 5839 Not specifying this option is equivalent to 5840 spectre_v2_user=auto. 5841 5842 spec_store_bypass_disable= 5843 [HW] Control Speculative Store Bypass (SSB) Disable mitigation 5844 (Speculative Store Bypass vulnerability) 5845 5846 Certain CPUs are vulnerable to an exploit against a 5847 a common industry wide performance optimization known 5848 as "Speculative Store Bypass" in which recent stores 5849 to the same memory location may not be observed by 5850 later loads during speculative execution. The idea 5851 is that such stores are unlikely and that they can 5852 be detected prior to instruction retirement at the 5853 end of a particular speculation execution window. 5854 5855 In vulnerable processors, the speculatively forwarded 5856 store can be used in a cache side channel attack, for 5857 example to read memory to which the attacker does not 5858 directly have access (e.g. inside sandboxed code). 5859 5860 This parameter controls whether the Speculative Store 5861 Bypass optimization is used. 5862 5863 On x86 the options are: 5864 5865 on - Unconditionally disable Speculative Store Bypass 5866 off - Unconditionally enable Speculative Store Bypass 5867 auto - Kernel detects whether the CPU model contains an 5868 implementation of Speculative Store Bypass and 5869 picks the most appropriate mitigation. If the 5870 CPU is not vulnerable, "off" is selected. If the 5871 CPU is vulnerable the default mitigation is 5872 architecture and Kconfig dependent. See below. 5873 prctl - Control Speculative Store Bypass per thread 5874 via prctl. Speculative Store Bypass is enabled 5875 for a process by default. The state of the control 5876 is inherited on fork. 5877 seccomp - Same as "prctl" above, but all seccomp threads 5878 will disable SSB unless they explicitly opt out. 5879 5880 Default mitigations: 5881 X86: "prctl" 5882 5883 On powerpc the options are: 5884 5885 on,auto - On Power8 and Power9 insert a store-forwarding 5886 barrier on kernel entry and exit. On Power7 5887 perform a software flush on kernel entry and 5888 exit. 5889 off - No action. 5890 5891 Not specifying this option is equivalent to 5892 spec_store_bypass_disable=auto. 5893 5894 spia_io_base= [HW,MTD] 5895 spia_fio_base= 5896 spia_pedr= 5897 spia_peddr= 5898 5899 split_lock_detect= 5900 [X86] Enable split lock detection or bus lock detection 5901 5902 When enabled (and if hardware support is present), atomic 5903 instructions that access data across cache line 5904 boundaries will result in an alignment check exception 5905 for split lock detection or a debug exception for 5906 bus lock detection. 5907 5908 off - not enabled 5909 5910 warn - the kernel will emit rate-limited warnings 5911 about applications triggering the #AC 5912 exception or the #DB exception. This mode is 5913 the default on CPUs that support split lock 5914 detection or bus lock detection. Default 5915 behavior is by #AC if both features are 5916 enabled in hardware. 5917 5918 fatal - the kernel will send SIGBUS to applications 5919 that trigger the #AC exception or the #DB 5920 exception. Default behavior is by #AC if 5921 both features are enabled in hardware. 5922 5923 ratelimit:N - 5924 Set system wide rate limit to N bus locks 5925 per second for bus lock detection. 5926 0 < N <= 1000. 5927 5928 N/A for split lock detection. 5929 5930 5931 If an #AC exception is hit in the kernel or in 5932 firmware (i.e. not while executing in user mode) 5933 the kernel will oops in either "warn" or "fatal" 5934 mode. 5935 5936 #DB exception for bus lock is triggered only when 5937 CPL > 0. 5938 5939 srbds= [X86,INTEL] 5940 Control the Special Register Buffer Data Sampling 5941 (SRBDS) mitigation. 5942 5943 Certain CPUs are vulnerable to an MDS-like 5944 exploit which can leak bits from the random 5945 number generator. 5946 5947 By default, this issue is mitigated by 5948 microcode. However, the microcode fix can cause 5949 the RDRAND and RDSEED instructions to become 5950 much slower. Among other effects, this will 5951 result in reduced throughput from /dev/urandom. 5952 5953 The microcode mitigation can be disabled with 5954 the following option: 5955 5956 off: Disable mitigation and remove 5957 performance impact to RDRAND and RDSEED 5958 5959 srcutree.big_cpu_lim [KNL] 5960 Specifies the number of CPUs constituting a 5961 large system, such that srcu_struct structures 5962 should immediately allocate an srcu_node array. 5963 This kernel-boot parameter defaults to 128, 5964 but takes effect only when the low-order four 5965 bits of srcutree.convert_to_big is equal to 3 5966 (decide at boot). 5967 5968 srcutree.convert_to_big [KNL] 5969 Specifies under what conditions an SRCU tree 5970 srcu_struct structure will be converted to big 5971 form, that is, with an rcu_node tree: 5972 5973 0: Never. 5974 1: At init_srcu_struct() time. 5975 2: When rcutorture decides to. 5976 3: Decide at boot time (default). 5977 0x1X: Above plus if high contention. 5978 5979 Either way, the srcu_node tree will be sized based 5980 on the actual runtime number of CPUs (nr_cpu_ids) 5981 instead of the compile-time CONFIG_NR_CPUS. 5982 5983 srcutree.counter_wrap_check [KNL] 5984 Specifies how frequently to check for 5985 grace-period sequence counter wrap for the 5986 srcu_data structure's ->srcu_gp_seq_needed field. 5987 The greater the number of bits set in this kernel 5988 parameter, the less frequently counter wrap will 5989 be checked for. Note that the bottom two bits 5990 are ignored. 5991 5992 srcutree.exp_holdoff [KNL] 5993 Specifies how many nanoseconds must elapse 5994 since the end of the last SRCU grace period for 5995 a given srcu_struct until the next normal SRCU 5996 grace period will be considered for automatic 5997 expediting. Set to zero to disable automatic 5998 expediting. 5999 6000 srcutree.srcu_max_nodelay [KNL] 6001 Specifies the number of no-delay instances 6002 per jiffy for which the SRCU grace period 6003 worker thread will be rescheduled with zero 6004 delay. Beyond this limit, worker thread will 6005 be rescheduled with a sleep delay of one jiffy. 6006 6007 srcutree.srcu_max_nodelay_phase [KNL] 6008 Specifies the per-grace-period phase, number of 6009 non-sleeping polls of readers. Beyond this limit, 6010 grace period worker thread will be rescheduled 6011 with a sleep delay of one jiffy, between each 6012 rescan of the readers, for a grace period phase. 6013 6014 srcutree.srcu_retry_check_delay [KNL] 6015 Specifies number of microseconds of non-sleeping 6016 delay between each non-sleeping poll of readers. 6017 6018 srcutree.small_contention_lim [KNL] 6019 Specifies the number of update-side contention 6020 events per jiffy will be tolerated before 6021 initiating a conversion of an srcu_struct 6022 structure to big form. Note that the value of 6023 srcutree.convert_to_big must have the 0x10 bit 6024 set for contention-based conversions to occur. 6025 6026 ssbd= [ARM64,HW] 6027 Speculative Store Bypass Disable control 6028 6029 On CPUs that are vulnerable to the Speculative 6030 Store Bypass vulnerability and offer a 6031 firmware based mitigation, this parameter 6032 indicates how the mitigation should be used: 6033 6034 force-on: Unconditionally enable mitigation for 6035 for both kernel and userspace 6036 force-off: Unconditionally disable mitigation for 6037 for both kernel and userspace 6038 kernel: Always enable mitigation in the 6039 kernel, and offer a prctl interface 6040 to allow userspace to register its 6041 interest in being mitigated too. 6042 6043 stack_guard_gap= [MM] 6044 override the default stack gap protection. The value 6045 is in page units and it defines how many pages prior 6046 to (for stacks growing down) resp. after (for stacks 6047 growing up) the main stack are reserved for no other 6048 mapping. Default value is 256 pages. 6049 6050 stack_depot_disable= [KNL] 6051 Setting this to true through kernel command line will 6052 disable the stack depot thereby saving the static memory 6053 consumed by the stack hash table. By default this is set 6054 to false. 6055 6056 stacktrace [FTRACE] 6057 Enabled the stack tracer on boot up. 6058 6059 stacktrace_filter=[function-list] 6060 [FTRACE] Limit the functions that the stack tracer 6061 will trace at boot up. function-list is a comma-separated 6062 list of functions. This list can be changed at run 6063 time by the stack_trace_filter file in the debugfs 6064 tracing directory. Note, this enables stack tracing 6065 and the stacktrace above is not needed. 6066 6067 sti= [PARISC,HW] 6068 Format: <num> 6069 Set the STI (builtin display/keyboard on the HP-PARISC 6070 machines) console (graphic card) which should be used 6071 as the initial boot-console. 6072 See also comment in drivers/video/console/sticore.c. 6073 6074 sti_font= [HW] 6075 See comment in drivers/video/console/sticore.c. 6076 6077 stifb= [HW] 6078 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 6079 6080 strict_sas_size= 6081 [X86] 6082 Format: <bool> 6083 Enable or disable strict sigaltstack size checks 6084 against the required signal frame size which 6085 depends on the supported FPU features. This can 6086 be used to filter out binaries which have 6087 not yet been made aware of AT_MINSIGSTKSZ. 6088 6089 stress_hpt [PPC] 6090 Limits the number of kernel HPT entries in the hash 6091 page table to increase the rate of hash page table 6092 faults on kernel addresses. 6093 6094 stress_slb [PPC] 6095 Limits the number of kernel SLB entries, and flushes 6096 them frequently to increase the rate of SLB faults 6097 on kernel addresses. 6098 6099 sunrpc.min_resvport= 6100 sunrpc.max_resvport= 6101 [NFS,SUNRPC] 6102 SunRPC servers often require that client requests 6103 originate from a privileged port (i.e. a port in the 6104 range 0 < portnr < 1024). 6105 An administrator who wishes to reserve some of these 6106 ports for other uses may adjust the range that the 6107 kernel's sunrpc client considers to be privileged 6108 using these two parameters to set the minimum and 6109 maximum port values. 6110 6111 sunrpc.svc_rpc_per_connection_limit= 6112 [NFS,SUNRPC] 6113 Limit the number of requests that the server will 6114 process in parallel from a single connection. 6115 The default value is 0 (no limit). 6116 6117 sunrpc.pool_mode= 6118 [NFS] 6119 Control how the NFS server code allocates CPUs to 6120 service thread pools. Depending on how many NICs 6121 you have and where their interrupts are bound, this 6122 option will affect which CPUs will do NFS serving. 6123 Note: this parameter cannot be changed while the 6124 NFS server is running. 6125 6126 auto the server chooses an appropriate mode 6127 automatically using heuristics 6128 global a single global pool contains all CPUs 6129 percpu one pool for each CPU 6130 pernode one pool for each NUMA node (equivalent 6131 to global on non-NUMA machines) 6132 6133 sunrpc.tcp_slot_table_entries= 6134 sunrpc.udp_slot_table_entries= 6135 [NFS,SUNRPC] 6136 Sets the upper limit on the number of simultaneous 6137 RPC calls that can be sent from the client to a 6138 server. Increasing these values may allow you to 6139 improve throughput, but will also increase the 6140 amount of memory reserved for use by the client. 6141 6142 suspend.pm_test_delay= 6143 [SUSPEND] 6144 Sets the number of seconds to remain in a suspend test 6145 mode before resuming the system (see 6146 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 6147 is set. Default value is 5. 6148 6149 svm= [PPC] 6150 Format: { on | off | y | n | 1 | 0 } 6151 This parameter controls use of the Protected 6152 Execution Facility on pSeries. 6153 6154 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 6155 Format: { <int> [,<int>] | force | noforce } 6156 <int> -- Number of I/O TLB slabs 6157 <int> -- Second integer after comma. Number of swiotlb 6158 areas with their own lock. Will be rounded up 6159 to a power of 2. 6160 force -- force using of bounce buffers even if they 6161 wouldn't be automatically used by the kernel 6162 noforce -- Never use bounce buffers (for debugging) 6163 6164 switches= [HW,M68k] 6165 6166 sysctl.*= [KNL] 6167 Set a sysctl parameter, right before loading the init 6168 process, as if the value was written to the respective 6169 /proc/sys/... file. Both '.' and '/' are recognized as 6170 separators. Unrecognized parameters and invalid values 6171 are reported in the kernel log. Sysctls registered 6172 later by a loaded module cannot be set this way. 6173 Example: sysctl.vm.swappiness=40 6174 6175 sysrq_always_enabled 6176 [KNL] 6177 Ignore sysrq setting - this boot parameter will 6178 neutralize any effect of /proc/sys/kernel/sysrq. 6179 Useful for debugging. 6180 6181 tcpmhash_entries= [KNL,NET] 6182 Set the number of tcp_metrics_hash slots. 6183 Default value is 8192 or 16384 depending on total 6184 ram pages. This is used to specify the TCP metrics 6185 cache size. See Documentation/networking/ip-sysctl.rst 6186 "tcp_no_metrics_save" section for more details. 6187 6188 tdfx= [HW,DRM] 6189 6190 test_suspend= [SUSPEND] 6191 Format: { "mem" | "standby" | "freeze" }[,N] 6192 Specify "mem" (for Suspend-to-RAM) or "standby" (for 6193 standby suspend) or "freeze" (for suspend type freeze) 6194 as the system sleep state during system startup with 6195 the optional capability to repeat N number of times. 6196 The system is woken from this state using a 6197 wakeup-capable RTC alarm. 6198 6199 thash_entries= [KNL,NET] 6200 Set number of hash buckets for TCP connection 6201 6202 thermal.act= [HW,ACPI] 6203 -1: disable all active trip points in all thermal zones 6204 <degrees C>: override all lowest active trip points 6205 6206 thermal.crt= [HW,ACPI] 6207 -1: disable all critical trip points in all thermal zones 6208 <degrees C>: override all critical trip points 6209 6210 thermal.nocrt= [HW,ACPI] 6211 Set to disable actions on ACPI thermal zone 6212 critical and hot trip points. 6213 6214 thermal.off= [HW,ACPI] 6215 1: disable ACPI thermal control 6216 6217 thermal.psv= [HW,ACPI] 6218 -1: disable all passive trip points 6219 <degrees C>: override all passive trip points to this 6220 value 6221 6222 thermal.tzp= [HW,ACPI] 6223 Specify global default ACPI thermal zone polling rate 6224 <deci-seconds>: poll all this frequency 6225 0: no polling (default) 6226 6227 threadirqs [KNL] 6228 Force threading of all interrupt handlers except those 6229 marked explicitly IRQF_NO_THREAD. 6230 6231 topology= [S390] 6232 Format: {off | on} 6233 Specify if the kernel should make use of the cpu 6234 topology information if the hardware supports this. 6235 The scheduler will make use of this information and 6236 e.g. base its process migration decisions on it. 6237 Default is on. 6238 6239 topology_updates= [KNL, PPC, NUMA] 6240 Format: {off} 6241 Specify if the kernel should ignore (off) 6242 topology updates sent by the hypervisor to this 6243 LPAR. 6244 6245 torture.disable_onoff_at_boot= [KNL] 6246 Prevent the CPU-hotplug component of torturing 6247 until after init has spawned. 6248 6249 torture.ftrace_dump_at_shutdown= [KNL] 6250 Dump the ftrace buffer at torture-test shutdown, 6251 even if there were no errors. This can be a 6252 very costly operation when many torture tests 6253 are running concurrently, especially on systems 6254 with rotating-rust storage. 6255 6256 torture.verbose_sleep_frequency= [KNL] 6257 Specifies how many verbose printk()s should be 6258 emitted between each sleep. The default of zero 6259 disables verbose-printk() sleeping. 6260 6261 torture.verbose_sleep_duration= [KNL] 6262 Duration of each verbose-printk() sleep in jiffies. 6263 6264 tp720= [HW,PS2] 6265 6266 tpm_suspend_pcr=[HW,TPM] 6267 Format: integer pcr id 6268 Specify that at suspend time, the tpm driver 6269 should extend the specified pcr with zeros, 6270 as a workaround for some chips which fail to 6271 flush the last written pcr on TPM_SaveState. 6272 This will guarantee that all the other pcrs 6273 are saved. 6274 6275 tp_printk [FTRACE] 6276 Have the tracepoints sent to printk as well as the 6277 tracing ring buffer. This is useful for early boot up 6278 where the system hangs or reboots and does not give the 6279 option for reading the tracing buffer or performing a 6280 ftrace_dump_on_oops. 6281 6282 To turn off having tracepoints sent to printk, 6283 echo 0 > /proc/sys/kernel/tracepoint_printk 6284 Note, echoing 1 into this file without the 6285 tracepoint_printk kernel cmdline option has no effect. 6286 6287 The tp_printk_stop_on_boot (see below) can also be used 6288 to stop the printing of events to console at 6289 late_initcall_sync. 6290 6291 ** CAUTION ** 6292 6293 Having tracepoints sent to printk() and activating high 6294 frequency tracepoints such as irq or sched, can cause 6295 the system to live lock. 6296 6297 tp_printk_stop_on_boot [FTRACE] 6298 When tp_printk (above) is set, it can cause a lot of noise 6299 on the console. It may be useful to only include the 6300 printing of events during boot up, as user space may 6301 make the system inoperable. 6302 6303 This command line option will stop the printing of events 6304 to console at the late_initcall_sync() time frame. 6305 6306 trace_buf_size=nn[KMG] 6307 [FTRACE] will set tracing buffer size on each cpu. 6308 6309 trace_clock= [FTRACE] Set the clock used for tracing events 6310 at boot up. 6311 local - Use the per CPU time stamp counter 6312 (converted into nanoseconds). Fast, but 6313 depending on the architecture, may not be 6314 in sync between CPUs. 6315 global - Event time stamps are synchronize across 6316 CPUs. May be slower than the local clock, 6317 but better for some race conditions. 6318 counter - Simple counting of events (1, 2, ..) 6319 note, some counts may be skipped due to the 6320 infrastructure grabbing the clock more than 6321 once per event. 6322 uptime - Use jiffies as the time stamp. 6323 perf - Use the same clock that perf uses. 6324 mono - Use ktime_get_mono_fast_ns() for time stamps. 6325 mono_raw - Use ktime_get_raw_fast_ns() for time 6326 stamps. 6327 boot - Use ktime_get_boot_fast_ns() for time stamps. 6328 Architectures may add more clocks. See 6329 Documentation/trace/ftrace.rst for more details. 6330 6331 trace_event=[event-list] 6332 [FTRACE] Set and start specified trace events in order 6333 to facilitate early boot debugging. The event-list is a 6334 comma-separated list of trace events to enable. See 6335 also Documentation/trace/events.rst 6336 6337 trace_instance=[instance-info] 6338 [FTRACE] Create a ring buffer instance early in boot up. 6339 This will be listed in: 6340 6341 /sys/kernel/tracing/instances 6342 6343 Events can be enabled at the time the instance is created 6344 via: 6345 6346 trace_instance=<name>,<system1>:<event1>,<system2>:<event2> 6347 6348 Note, the "<system*>:" portion is optional if the event is 6349 unique. 6350 6351 trace_instance=foo,sched:sched_switch,irq_handler_entry,initcall 6352 6353 will enable the "sched_switch" event (note, the "sched:" is optional, and 6354 the same thing would happen if it was left off). The irq_handler_entry 6355 event, and all events under the "initcall" system. 6356 6357 trace_options=[option-list] 6358 [FTRACE] Enable or disable tracer options at boot. 6359 The option-list is a comma delimited list of options 6360 that can be enabled or disabled just as if you were 6361 to echo the option name into 6362 6363 /sys/kernel/tracing/trace_options 6364 6365 For example, to enable stacktrace option (to dump the 6366 stack trace of each event), add to the command line: 6367 6368 trace_options=stacktrace 6369 6370 See also Documentation/trace/ftrace.rst "trace options" 6371 section. 6372 6373 trace_trigger=[trigger-list] 6374 [FTRACE] Add a event trigger on specific events. 6375 Set a trigger on top of a specific event, with an optional 6376 filter. 6377 6378 The format is is "trace_trigger=<event>.<trigger>[ if <filter>],..." 6379 Where more than one trigger may be specified that are comma deliminated. 6380 6381 For example: 6382 6383 trace_trigger="sched_switch.stacktrace if prev_state == 2" 6384 6385 The above will enable the "stacktrace" trigger on the "sched_switch" 6386 event but only trigger it if the "prev_state" of the "sched_switch" 6387 event is "2" (TASK_UNINTERUPTIBLE). 6388 6389 See also "Event triggers" in Documentation/trace/events.rst 6390 6391 6392 traceoff_on_warning 6393 [FTRACE] enable this option to disable tracing when a 6394 warning is hit. This turns off "tracing_on". Tracing can 6395 be enabled again by echoing '1' into the "tracing_on" 6396 file located in /sys/kernel/tracing/ 6397 6398 This option is useful, as it disables the trace before 6399 the WARNING dump is called, which prevents the trace to 6400 be filled with content caused by the warning output. 6401 6402 This option can also be set at run time via the sysctl 6403 option: kernel/traceoff_on_warning 6404 6405 transparent_hugepage= 6406 [KNL] 6407 Format: [always|madvise|never] 6408 Can be used to control the default behavior of the system 6409 with respect to transparent hugepages. 6410 See Documentation/admin-guide/mm/transhuge.rst 6411 for more details. 6412 6413 trusted.source= [KEYS] 6414 Format: <string> 6415 This parameter identifies the trust source as a backend 6416 for trusted keys implementation. Supported trust 6417 sources: 6418 - "tpm" 6419 - "tee" 6420 - "caam" 6421 If not specified then it defaults to iterating through 6422 the trust source list starting with TPM and assigns the 6423 first trust source as a backend which is initialized 6424 successfully during iteration. 6425 6426 trusted.rng= [KEYS] 6427 Format: <string> 6428 The RNG used to generate key material for trusted keys. 6429 Can be one of: 6430 - "kernel" 6431 - the same value as trusted.source: "tpm" or "tee" 6432 - "default" 6433 If not specified, "default" is used. In this case, 6434 the RNG's choice is left to each individual trust source. 6435 6436 tsc= Disable clocksource stability checks for TSC. 6437 Format: <string> 6438 [x86] reliable: mark tsc clocksource as reliable, this 6439 disables clocksource verification at runtime, as well 6440 as the stability checks done at bootup. Used to enable 6441 high-resolution timer mode on older hardware, and in 6442 virtualized environment. 6443 [x86] noirqtime: Do not use TSC to do irq accounting. 6444 Used to run time disable IRQ_TIME_ACCOUNTING on any 6445 platforms where RDTSC is slow and this accounting 6446 can add overhead. 6447 [x86] unstable: mark the TSC clocksource as unstable, this 6448 marks the TSC unconditionally unstable at bootup and 6449 avoids any further wobbles once the TSC watchdog notices. 6450 [x86] nowatchdog: disable clocksource watchdog. Used 6451 in situations with strict latency requirements (where 6452 interruptions from clocksource watchdog are not 6453 acceptable). 6454 [x86] recalibrate: force recalibration against a HW timer 6455 (HPET or PM timer) on systems whose TSC frequency was 6456 obtained from HW or FW using either an MSR or CPUID(0x15). 6457 Warn if the difference is more than 500 ppm. 6458 [x86] watchdog: Use TSC as the watchdog clocksource with 6459 which to check other HW timers (HPET or PM timer), but 6460 only on systems where TSC has been deemed trustworthy. 6461 This will be suppressed by an earlier tsc=nowatchdog and 6462 can be overridden by a later tsc=nowatchdog. A console 6463 message will flag any such suppression or overriding. 6464 6465 tsc_early_khz= [X86] Skip early TSC calibration and use the given 6466 value instead. Useful when the early TSC frequency discovery 6467 procedure is not reliable, such as on overclocked systems 6468 with CPUID.16h support and partial CPUID.15h support. 6469 Format: <unsigned int> 6470 6471 tsx= [X86] Control Transactional Synchronization 6472 Extensions (TSX) feature in Intel processors that 6473 support TSX control. 6474 6475 This parameter controls the TSX feature. The options are: 6476 6477 on - Enable TSX on the system. Although there are 6478 mitigations for all known security vulnerabilities, 6479 TSX has been known to be an accelerator for 6480 several previous speculation-related CVEs, and 6481 so there may be unknown security risks associated 6482 with leaving it enabled. 6483 6484 off - Disable TSX on the system. (Note that this 6485 option takes effect only on newer CPUs which are 6486 not vulnerable to MDS, i.e., have 6487 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 6488 the new IA32_TSX_CTRL MSR through a microcode 6489 update. This new MSR allows for the reliable 6490 deactivation of the TSX functionality.) 6491 6492 auto - Disable TSX if X86_BUG_TAA is present, 6493 otherwise enable TSX on the system. 6494 6495 Not specifying this option is equivalent to tsx=off. 6496 6497 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 6498 for more details. 6499 6500 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async 6501 Abort (TAA) vulnerability. 6502 6503 Similar to Micro-architectural Data Sampling (MDS) 6504 certain CPUs that support Transactional 6505 Synchronization Extensions (TSX) are vulnerable to an 6506 exploit against CPU internal buffers which can forward 6507 information to a disclosure gadget under certain 6508 conditions. 6509 6510 In vulnerable processors, the speculatively forwarded 6511 data can be used in a cache side channel attack, to 6512 access data to which the attacker does not have direct 6513 access. 6514 6515 This parameter controls the TAA mitigation. The 6516 options are: 6517 6518 full - Enable TAA mitigation on vulnerable CPUs 6519 if TSX is enabled. 6520 6521 full,nosmt - Enable TAA mitigation and disable SMT on 6522 vulnerable CPUs. If TSX is disabled, SMT 6523 is not disabled because CPU is not 6524 vulnerable to cross-thread TAA attacks. 6525 off - Unconditionally disable TAA mitigation 6526 6527 On MDS-affected machines, tsx_async_abort=off can be 6528 prevented by an active MDS mitigation as both vulnerabilities 6529 are mitigated with the same mechanism so in order to disable 6530 this mitigation, you need to specify mds=off too. 6531 6532 Not specifying this option is equivalent to 6533 tsx_async_abort=full. On CPUs which are MDS affected 6534 and deploy MDS mitigation, TAA mitigation is not 6535 required and doesn't provide any additional 6536 mitigation. 6537 6538 For details see: 6539 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 6540 6541 turbografx.map[2|3]= [HW,JOY] 6542 TurboGraFX parallel port interface 6543 Format: 6544 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 6545 See also Documentation/input/devices/joystick-parport.rst 6546 6547 udbg-immortal [PPC] When debugging early kernel crashes that 6548 happen after console_init() and before a proper 6549 console driver takes over, this boot options might 6550 help "seeing" what's going on. 6551 6552 uhash_entries= [KNL,NET] 6553 Set number of hash buckets for UDP/UDP-Lite connections 6554 6555 uhci-hcd.ignore_oc= 6556 [USB] Ignore overcurrent events (default N). 6557 Some badly-designed motherboards generate lots of 6558 bogus events, for ports that aren't wired to 6559 anything. Set this parameter to avoid log spamming. 6560 Note that genuine overcurrent events won't be 6561 reported either. 6562 6563 unknown_nmi_panic 6564 [X86] Cause panic on unknown NMI. 6565 6566 usbcore.authorized_default= 6567 [USB] Default USB device authorization: 6568 (default -1 = authorized except for wireless USB, 6569 0 = not authorized, 1 = authorized, 2 = authorized 6570 if device connected to internal port) 6571 6572 usbcore.autosuspend= 6573 [USB] The autosuspend time delay (in seconds) used 6574 for newly-detected USB devices (default 2). This 6575 is the time required before an idle device will be 6576 autosuspended. Devices for which the delay is set 6577 to a negative value won't be autosuspended at all. 6578 6579 usbcore.usbfs_snoop= 6580 [USB] Set to log all usbfs traffic (default 0 = off). 6581 6582 usbcore.usbfs_snoop_max= 6583 [USB] Maximum number of bytes to snoop in each URB 6584 (default = 65536). 6585 6586 usbcore.blinkenlights= 6587 [USB] Set to cycle leds on hubs (default 0 = off). 6588 6589 usbcore.old_scheme_first= 6590 [USB] Start with the old device initialization 6591 scheme (default 0 = off). 6592 6593 usbcore.usbfs_memory_mb= 6594 [USB] Memory limit (in MB) for buffers allocated by 6595 usbfs (default = 16, 0 = max = 2047). 6596 6597 usbcore.use_both_schemes= 6598 [USB] Try the other device initialization scheme 6599 if the first one fails (default 1 = enabled). 6600 6601 usbcore.initial_descriptor_timeout= 6602 [USB] Specifies timeout for the initial 64-byte 6603 USB_REQ_GET_DESCRIPTOR request in milliseconds 6604 (default 5000 = 5.0 seconds). 6605 6606 usbcore.nousb [USB] Disable the USB subsystem 6607 6608 usbcore.quirks= 6609 [USB] A list of quirk entries to augment the built-in 6610 usb core quirk list. List entries are separated by 6611 commas. Each entry has the form 6612 VendorID:ProductID:Flags. The IDs are 4-digit hex 6613 numbers and Flags is a set of letters. Each letter 6614 will change the built-in quirk; setting it if it is 6615 clear and clearing it if it is set. The letters have 6616 the following meanings: 6617 a = USB_QUIRK_STRING_FETCH_255 (string 6618 descriptors must not be fetched using 6619 a 255-byte read); 6620 b = USB_QUIRK_RESET_RESUME (device can't resume 6621 correctly so reset it instead); 6622 c = USB_QUIRK_NO_SET_INTF (device can't handle 6623 Set-Interface requests); 6624 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 6625 handle its Configuration or Interface 6626 strings); 6627 e = USB_QUIRK_RESET (device can't be reset 6628 (e.g morph devices), don't use reset); 6629 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 6630 more interface descriptions than the 6631 bNumInterfaces count, and can't handle 6632 talking to these interfaces); 6633 g = USB_QUIRK_DELAY_INIT (device needs a pause 6634 during initialization, after we read 6635 the device descriptor); 6636 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 6637 high speed and super speed interrupt 6638 endpoints, the USB 2.0 and USB 3.0 spec 6639 require the interval in microframes (1 6640 microframe = 125 microseconds) to be 6641 calculated as interval = 2 ^ 6642 (bInterval-1). 6643 Devices with this quirk report their 6644 bInterval as the result of this 6645 calculation instead of the exponent 6646 variable used in the calculation); 6647 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 6648 handle device_qualifier descriptor 6649 requests); 6650 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 6651 generates spurious wakeup, ignore 6652 remote wakeup capability); 6653 k = USB_QUIRK_NO_LPM (device can't handle Link 6654 Power Management); 6655 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 6656 (Device reports its bInterval as linear 6657 frames instead of the USB 2.0 6658 calculation); 6659 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 6660 to be disconnected before suspend to 6661 prevent spurious wakeup); 6662 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 6663 pause after every control message); 6664 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 6665 delay after resetting its port); 6666 Example: quirks=0781:5580:bk,0a5c:5834:gij 6667 6668 usbhid.mousepoll= 6669 [USBHID] The interval which mice are to be polled at. 6670 6671 usbhid.jspoll= 6672 [USBHID] The interval which joysticks are to be polled at. 6673 6674 usbhid.kbpoll= 6675 [USBHID] The interval which keyboards are to be polled at. 6676 6677 usb-storage.delay_use= 6678 [UMS] The delay in seconds before a new device is 6679 scanned for Logical Units (default 1). 6680 6681 usb-storage.quirks= 6682 [UMS] A list of quirks entries to supplement or 6683 override the built-in unusual_devs list. List 6684 entries are separated by commas. Each entry has 6685 the form VID:PID:Flags where VID and PID are Vendor 6686 and Product ID values (4-digit hex numbers) and 6687 Flags is a set of characters, each corresponding 6688 to a common usb-storage quirk flag as follows: 6689 a = SANE_SENSE (collect more than 18 bytes 6690 of sense data, not on uas); 6691 b = BAD_SENSE (don't collect more than 18 6692 bytes of sense data, not on uas); 6693 c = FIX_CAPACITY (decrease the reported 6694 device capacity by one sector); 6695 d = NO_READ_DISC_INFO (don't use 6696 READ_DISC_INFO command, not on uas); 6697 e = NO_READ_CAPACITY_16 (don't use 6698 READ_CAPACITY_16 command); 6699 f = NO_REPORT_OPCODES (don't use report opcodes 6700 command, uas only); 6701 g = MAX_SECTORS_240 (don't transfer more than 6702 240 sectors at a time, uas only); 6703 h = CAPACITY_HEURISTICS (decrease the 6704 reported device capacity by one 6705 sector if the number is odd); 6706 i = IGNORE_DEVICE (don't bind to this 6707 device); 6708 j = NO_REPORT_LUNS (don't use report luns 6709 command, uas only); 6710 k = NO_SAME (do not use WRITE_SAME, uas only) 6711 l = NOT_LOCKABLE (don't try to lock and 6712 unlock ejectable media, not on uas); 6713 m = MAX_SECTORS_64 (don't transfer more 6714 than 64 sectors = 32 KB at a time, 6715 not on uas); 6716 n = INITIAL_READ10 (force a retry of the 6717 initial READ(10) command, not on uas); 6718 o = CAPACITY_OK (accept the capacity 6719 reported by the device, not on uas); 6720 p = WRITE_CACHE (the device cache is ON 6721 by default, not on uas); 6722 r = IGNORE_RESIDUE (the device reports 6723 bogus residue values, not on uas); 6724 s = SINGLE_LUN (the device has only one 6725 Logical Unit); 6726 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 6727 commands, uas only); 6728 u = IGNORE_UAS (don't bind to the uas driver); 6729 w = NO_WP_DETECT (don't test whether the 6730 medium is write-protected). 6731 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 6732 even if the device claims no cache, 6733 not on uas) 6734 Example: quirks=0419:aaf5:rl,0421:0433:rc 6735 6736 user_debug= [KNL,ARM] 6737 Format: <int> 6738 See arch/arm/Kconfig.debug help text. 6739 1 - undefined instruction events 6740 2 - system calls 6741 4 - invalid data aborts 6742 8 - SIGSEGV faults 6743 16 - SIGBUS faults 6744 Example: user_debug=31 6745 6746 userpte= 6747 [X86] Flags controlling user PTE allocations. 6748 6749 nohigh = do not allocate PTE pages in 6750 HIGHMEM regardless of setting 6751 of CONFIG_HIGHPTE. 6752 6753 vdso= [X86,SH,SPARC] 6754 On X86_32, this is an alias for vdso32=. Otherwise: 6755 6756 vdso=1: enable VDSO (the default) 6757 vdso=0: disable VDSO mapping 6758 6759 vdso32= [X86] Control the 32-bit vDSO 6760 vdso32=1: enable 32-bit VDSO 6761 vdso32=0 or vdso32=2: disable 32-bit VDSO 6762 6763 See the help text for CONFIG_COMPAT_VDSO for more 6764 details. If CONFIG_COMPAT_VDSO is set, the default is 6765 vdso32=0; otherwise, the default is vdso32=1. 6766 6767 For compatibility with older kernels, vdso32=2 is an 6768 alias for vdso32=0. 6769 6770 Try vdso32=0 if you encounter an error that says: 6771 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 6772 6773 vector= [IA-64,SMP] 6774 vector=percpu: enable percpu vector domain 6775 6776 video= [FB] Frame buffer configuration 6777 See Documentation/fb/modedb.rst. 6778 6779 video.brightness_switch_enabled= [ACPI] 6780 Format: [0|1] 6781 If set to 1, on receiving an ACPI notify event 6782 generated by hotkey, video driver will adjust brightness 6783 level and then send out the event to user space through 6784 the allocated input device. If set to 0, video driver 6785 will only send out the event without touching backlight 6786 brightness level. 6787 default: 1 6788 6789 virtio_mmio.device= 6790 [VMMIO] Memory mapped virtio (platform) device. 6791 6792 <size>@<baseaddr>:<irq>[:<id>] 6793 where: 6794 <size> := size (can use standard suffixes 6795 like K, M and G) 6796 <baseaddr> := physical base address 6797 <irq> := interrupt number (as passed to 6798 request_irq()) 6799 <id> := (optional) platform device id 6800 example: 6801 virtio_mmio.device=1K@0x100b0000:48:7 6802 6803 Can be used multiple times for multiple devices. 6804 6805 vga= [BOOT,X86-32] Select a particular video mode 6806 See Documentation/arch/x86/boot.rst and 6807 Documentation/admin-guide/svga.rst. 6808 Use vga=ask for menu. 6809 This is actually a boot loader parameter; the value is 6810 passed to the kernel using a special protocol. 6811 6812 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 6813 May slow down system boot speed, especially when 6814 enabled on systems with a large amount of memory. 6815 All options are enabled by default, and this 6816 interface is meant to allow for selectively 6817 enabling or disabling specific virtual memory 6818 debugging features. 6819 6820 Available options are: 6821 P Enable page structure init time poisoning 6822 - Disable all of the above options 6823 6824 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 6825 size of <nn>. This can be used to increase the 6826 minimum size (128MB on x86). It can also be used to 6827 decrease the size and leave more room for directly 6828 mapped kernel RAM. 6829 6830 vmcp_cma=nn[MG] [KNL,S390] 6831 Sets the memory size reserved for contiguous memory 6832 allocations for the vmcp device driver. 6833 6834 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 6835 Format: <command> 6836 6837 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 6838 Format: <command> 6839 6840 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 6841 Format: <command> 6842 6843 vsyscall= [X86-64] 6844 Controls the behavior of vsyscalls (i.e. calls to 6845 fixed addresses of 0xffffffffff600x00 from legacy 6846 code). Most statically-linked binaries and older 6847 versions of glibc use these calls. Because these 6848 functions are at fixed addresses, they make nice 6849 targets for exploits that can control RIP. 6850 6851 emulate Vsyscalls turn into traps and are emulated 6852 reasonably safely. The vsyscall page is 6853 readable. 6854 6855 xonly [default] Vsyscalls turn into traps and are 6856 emulated reasonably safely. The vsyscall 6857 page is not readable. 6858 6859 none Vsyscalls don't work at all. This makes 6860 them quite hard to use for exploits but 6861 might break your system. 6862 6863 vt.color= [VT] Default text color. 6864 Format: 0xYX, X = foreground, Y = background. 6865 Default: 0x07 = light gray on black. 6866 6867 vt.cur_default= [VT] Default cursor shape. 6868 Format: 0xCCBBAA, where AA, BB, and CC are the same as 6869 the parameters of the <Esc>[?A;B;Cc escape sequence; 6870 see VGA-softcursor.txt. Default: 2 = underline. 6871 6872 vt.default_blu= [VT] 6873 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 6874 Change the default blue palette of the console. 6875 This is a 16-member array composed of values 6876 ranging from 0-255. 6877 6878 vt.default_grn= [VT] 6879 Format: <green0>,<green1>,<green2>,...,<green15> 6880 Change the default green palette of the console. 6881 This is a 16-member array composed of values 6882 ranging from 0-255. 6883 6884 vt.default_red= [VT] 6885 Format: <red0>,<red1>,<red2>,...,<red15> 6886 Change the default red palette of the console. 6887 This is a 16-member array composed of values 6888 ranging from 0-255. 6889 6890 vt.default_utf8= 6891 [VT] 6892 Format=<0|1> 6893 Set system-wide default UTF-8 mode for all tty's. 6894 Default is 1, i.e. UTF-8 mode is enabled for all 6895 newly opened terminals. 6896 6897 vt.global_cursor_default= 6898 [VT] 6899 Format=<-1|0|1> 6900 Set system-wide default for whether a cursor 6901 is shown on new VTs. Default is -1, 6902 i.e. cursors will be created by default unless 6903 overridden by individual drivers. 0 will hide 6904 cursors, 1 will display them. 6905 6906 vt.italic= [VT] Default color for italic text; 0-15. 6907 Default: 2 = green. 6908 6909 vt.underline= [VT] Default color for underlined text; 0-15. 6910 Default: 3 = cyan. 6911 6912 watchdog timers [HW,WDT] For information on watchdog timers, 6913 see Documentation/watchdog/watchdog-parameters.rst 6914 or other driver-specific files in the 6915 Documentation/watchdog/ directory. 6916 6917 watchdog_thresh= 6918 [KNL] 6919 Set the hard lockup detector stall duration 6920 threshold in seconds. The soft lockup detector 6921 threshold is set to twice the value. A value of 0 6922 disables both lockup detectors. Default is 10 6923 seconds. 6924 6925 workqueue.watchdog_thresh= 6926 If CONFIG_WQ_WATCHDOG is configured, workqueue can 6927 warn stall conditions and dump internal state to 6928 help debugging. 0 disables workqueue stall 6929 detection; otherwise, it's the stall threshold 6930 duration in seconds. The default value is 30 and 6931 it can be updated at runtime by writing to the 6932 corresponding sysfs file. 6933 6934 workqueue.disable_numa 6935 By default, all work items queued to unbound 6936 workqueues are affine to the NUMA nodes they're 6937 issued on, which results in better behavior in 6938 general. If NUMA affinity needs to be disabled for 6939 whatever reason, this option can be used. Note 6940 that this also can be controlled per-workqueue for 6941 workqueues visible under /sys/bus/workqueue/. 6942 6943 workqueue.power_efficient 6944 Per-cpu workqueues are generally preferred because 6945 they show better performance thanks to cache 6946 locality; unfortunately, per-cpu workqueues tend to 6947 be more power hungry than unbound workqueues. 6948 6949 Enabling this makes the per-cpu workqueues which 6950 were observed to contribute significantly to power 6951 consumption unbound, leading to measurably lower 6952 power usage at the cost of small performance 6953 overhead. 6954 6955 The default value of this parameter is determined by 6956 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 6957 6958 workqueue.debug_force_rr_cpu 6959 Workqueue used to implicitly guarantee that work 6960 items queued without explicit CPU specified are put 6961 on the local CPU. This guarantee is no longer true 6962 and while local CPU is still preferred work items 6963 may be put on foreign CPUs. This debug option 6964 forces round-robin CPU selection to flush out 6965 usages which depend on the now broken guarantee. 6966 When enabled, memory and cache locality will be 6967 impacted. 6968 6969 writecombine= [LOONGARCH] Control the MAT (Memory Access Type) of 6970 ioremap_wc(). 6971 6972 on - Enable writecombine, use WUC for ioremap_wc() 6973 off - Disable writecombine, use SUC for ioremap_wc() 6974 6975 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 6976 default x2apic cluster mode on platforms 6977 supporting x2apic. 6978 6979 xen_512gb_limit [KNL,X86-64,XEN] 6980 Restricts the kernel running paravirtualized under Xen 6981 to use only up to 512 GB of RAM. The reason to do so is 6982 crash analysis tools and Xen tools for doing domain 6983 save/restore/migration must be enabled to handle larger 6984 domains. 6985 6986 xen_emul_unplug= [HW,X86,XEN] 6987 Unplug Xen emulated devices 6988 Format: [unplug0,][unplug1] 6989 ide-disks -- unplug primary master IDE devices 6990 aux-ide-disks -- unplug non-primary-master IDE devices 6991 nics -- unplug network devices 6992 all -- unplug all emulated devices (NICs and IDE disks) 6993 unnecessary -- unplugging emulated devices is 6994 unnecessary even if the host did not respond to 6995 the unplug protocol 6996 never -- do not unplug even if version check succeeds 6997 6998 xen_legacy_crash [X86,XEN] 6999 Crash from Xen panic notifier, without executing late 7000 panic() code such as dumping handler. 7001 7002 xen_msr_safe= [X86,XEN] 7003 Format: <bool> 7004 Select whether to always use non-faulting (safe) MSR 7005 access functions when running as Xen PV guest. The 7006 default value is controlled by CONFIG_XEN_PV_MSR_SAFE. 7007 7008 xen_nopvspin [X86,XEN] 7009 Disables the qspinlock slowpath using Xen PV optimizations. 7010 This parameter is obsoleted by "nopvspin" parameter, which 7011 has equivalent effect for XEN platform. 7012 7013 xen_nopv [X86] 7014 Disables the PV optimizations forcing the HVM guest to 7015 run as generic HVM guest with no PV drivers. 7016 This option is obsoleted by the "nopv" option, which 7017 has equivalent effect for XEN platform. 7018 7019 xen_no_vector_callback 7020 [KNL,X86,XEN] Disable the vector callback for Xen 7021 event channel interrupts. 7022 7023 xen_scrub_pages= [XEN] 7024 Boolean option to control scrubbing pages before giving them back 7025 to Xen, for use by other domains. Can be also changed at runtime 7026 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 7027 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 7028 7029 xen_timer_slop= [X86-64,XEN] 7030 Set the timer slop (in nanoseconds) for the virtual Xen 7031 timers (default is 100000). This adjusts the minimum 7032 delta of virtualized Xen timers, where lower values 7033 improve timer resolution at the expense of processing 7034 more timer interrupts. 7035 7036 xen.balloon_boot_timeout= [XEN] 7037 The time (in seconds) to wait before giving up to boot 7038 in case initial ballooning fails to free enough memory. 7039 Applies only when running as HVM or PVH guest and 7040 started with less memory configured than allowed at 7041 max. Default is 180. 7042 7043 xen.event_eoi_delay= [XEN] 7044 How long to delay EOI handling in case of event 7045 storms (jiffies). Default is 10. 7046 7047 xen.event_loop_timeout= [XEN] 7048 After which time (jiffies) the event handling loop 7049 should start to delay EOI handling. Default is 2. 7050 7051 xen.fifo_events= [XEN] 7052 Boolean parameter to disable using fifo event handling 7053 even if available. Normally fifo event handling is 7054 preferred over the 2-level event handling, as it is 7055 fairer and the number of possible event channels is 7056 much higher. Default is on (use fifo events). 7057 7058 xirc2ps_cs= [NET,PCMCIA] 7059 Format: 7060 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 7061 7062 xive= [PPC] 7063 By default on POWER9 and above, the kernel will 7064 natively use the XIVE interrupt controller. This option 7065 allows the fallback firmware mode to be used: 7066 7067 off Fallback to firmware control of XIVE interrupt 7068 controller on both pseries and powernv 7069 platforms. Only useful on POWER9 and above. 7070 7071 xive.store-eoi=off [PPC] 7072 By default on POWER10 and above, the kernel will use 7073 stores for EOI handling when the XIVE interrupt mode 7074 is active. This option allows the XIVE driver to use 7075 loads instead, as on POWER9. 7076 7077 xhci-hcd.quirks [USB,KNL] 7078 A hex value specifying bitmask with supplemental xhci 7079 host controller quirks. Meaning of each bit can be 7080 consulted in header drivers/usb/host/xhci.h. 7081 7082 xmon [PPC] 7083 Format: { early | on | rw | ro | off } 7084 Controls if xmon debugger is enabled. Default is off. 7085 Passing only "xmon" is equivalent to "xmon=early". 7086 early Call xmon as early as possible on boot; xmon 7087 debugger is called from setup_arch(). 7088 on xmon debugger hooks will be installed so xmon 7089 is only called on a kernel crash. Default mode, 7090 i.e. either "ro" or "rw" mode, is controlled 7091 with CONFIG_XMON_DEFAULT_RO_MODE. 7092 rw xmon debugger hooks will be installed so xmon 7093 is called only on a kernel crash, mode is write, 7094 meaning SPR registers, memory and, other data 7095 can be written using xmon commands. 7096 ro same as "rw" option above but SPR registers, 7097 memory, and other data can't be written using 7098 xmon commands. 7099 off xmon is disabled. 7100 7101