1Linux kernel release 4.x <http://kernel.org/> 2============================================= 3 4These are the release notes for Linux version 4. Read them carefully, 5as they tell you what this is all about, explain how to install the 6kernel, and what to do if something goes wrong. 7 8What is Linux? 9-------------- 10 11 Linux is a clone of the operating system Unix, written from scratch by 12 Linus Torvalds with assistance from a loosely-knit team of hackers across 13 the Net. It aims towards POSIX and Single UNIX Specification compliance. 14 15 It has all the features you would expect in a modern fully-fledged Unix, 16 including true multitasking, virtual memory, shared libraries, demand 17 loading, shared copy-on-write executables, proper memory management, 18 and multistack networking including IPv4 and IPv6. 19 20 It is distributed under the GNU General Public License v2 - see the 21 accompanying COPYING file for more details. 22 23On what hardware does it run? 24----------------------------- 25 26 Although originally developed first for 32-bit x86-based PCs (386 or higher), 27 today Linux also runs on (at least) the Compaq Alpha AXP, Sun SPARC and 28 UltraSPARC, Motorola 68000, PowerPC, PowerPC64, ARM, Hitachi SuperH, Cell, 29 IBM S/390, MIPS, HP PA-RISC, Intel IA-64, DEC VAX, AMD x86-64, AXIS CRIS, 30 Xtensa, Tilera TILE, ARC and Renesas M32R architectures. 31 32 Linux is easily portable to most general-purpose 32- or 64-bit architectures 33 as long as they have a paged memory management unit (PMMU) and a port of the 34 GNU C compiler (gcc) (part of The GNU Compiler Collection, GCC). Linux has 35 also been ported to a number of architectures without a PMMU, although 36 functionality is then obviously somewhat limited. 37 Linux has also been ported to itself. You can now run the kernel as a 38 userspace application - this is called UserMode Linux (UML). 39 40Documentation 41------------- 42 43 - There is a lot of documentation available both in electronic form on 44 the Internet and in books, both Linux-specific and pertaining to 45 general UNIX questions. I'd recommend looking into the documentation 46 subdirectories on any Linux FTP site for the LDP (Linux Documentation 47 Project) books. This README is not meant to be documentation on the 48 system: there are much better sources available. 49 50 - There are various README files in the Documentation/ subdirectory: 51 these typically contain kernel-specific installation notes for some 52 drivers for example. See Documentation/00-INDEX for a list of what 53 is contained in each file. Please read the 54 :ref:`Documentation/process/changes.rst <changes>` file, as it 55 contains information about the problems, which may result by upgrading 56 your kernel. 57 58Installing the kernel source 59---------------------------- 60 61 - If you install the full sources, put the kernel tarball in a 62 directory where you have permissions (e.g. your home directory) and 63 unpack it:: 64 65 xz -cd linux-4.X.tar.xz | tar xvf - 66 67 Replace "X" with the version number of the latest kernel. 68 69 Do NOT use the /usr/src/linux area! This area has a (usually 70 incomplete) set of kernel headers that are used by the library header 71 files. They should match the library, and not get messed up by 72 whatever the kernel-du-jour happens to be. 73 74 - You can also upgrade between 4.x releases by patching. Patches are 75 distributed in the xz format. To install by patching, get all the 76 newer patch files, enter the top level directory of the kernel source 77 (linux-4.X) and execute:: 78 79 xz -cd ../patch-4.x.xz | patch -p1 80 81 Replace "x" for all versions bigger than the version "X" of your current 82 source tree, **in_order**, and you should be ok. You may want to remove 83 the backup files (some-file-name~ or some-file-name.orig), and make sure 84 that there are no failed patches (some-file-name# or some-file-name.rej). 85 If there are, either you or I have made a mistake. 86 87 Unlike patches for the 4.x kernels, patches for the 4.x.y kernels 88 (also known as the -stable kernels) are not incremental but instead apply 89 directly to the base 4.x kernel. For example, if your base kernel is 4.0 90 and you want to apply the 4.0.3 patch, you must not first apply the 4.0.1 91 and 4.0.2 patches. Similarly, if you are running kernel version 4.0.2 and 92 want to jump to 4.0.3, you must first reverse the 4.0.2 patch (that is, 93 patch -R) **before** applying the 4.0.3 patch. You can read more on this in 94 :ref:`Documentation/process/applying-patches.rst <applying_patches>`. 95 96 Alternatively, the script patch-kernel can be used to automate this 97 process. It determines the current kernel version and applies any 98 patches found:: 99 100 linux/scripts/patch-kernel linux 101 102 The first argument in the command above is the location of the 103 kernel source. Patches are applied from the current directory, but 104 an alternative directory can be specified as the second argument. 105 106 - Make sure you have no stale .o files and dependencies lying around:: 107 108 cd linux 109 make mrproper 110 111 You should now have the sources correctly installed. 112 113Software requirements 114--------------------- 115 116 Compiling and running the 4.x kernels requires up-to-date 117 versions of various software packages. Consult 118 :ref:`Documentation/process/changes.rst <changes>` for the minimum version numbers 119 required and how to get updates for these packages. Beware that using 120 excessively old versions of these packages can cause indirect 121 errors that are very difficult to track down, so don't assume that 122 you can just update packages when obvious problems arise during 123 build or operation. 124 125Build directory for the kernel 126------------------------------ 127 128 When compiling the kernel, all output files will per default be 129 stored together with the kernel source code. 130 Using the option ``make O=output/dir`` allows you to specify an alternate 131 place for the output files (including .config). 132 Example:: 133 134 kernel source code: /usr/src/linux-4.X 135 build directory: /home/name/build/kernel 136 137 To configure and build the kernel, use:: 138 139 cd /usr/src/linux-4.X 140 make O=/home/name/build/kernel menuconfig 141 make O=/home/name/build/kernel 142 sudo make O=/home/name/build/kernel modules_install install 143 144 Please note: If the ``O=output/dir`` option is used, then it must be 145 used for all invocations of make. 146 147Configuring the kernel 148---------------------- 149 150 Do not skip this step even if you are only upgrading one minor 151 version. New configuration options are added in each release, and 152 odd problems will turn up if the configuration files are not set up 153 as expected. If you want to carry your existing configuration to a 154 new version with minimal work, use ``make oldconfig``, which will 155 only ask you for the answers to new questions. 156 157 - Alternative configuration commands are:: 158 159 "make config" Plain text interface. 160 161 "make menuconfig" Text based color menus, radiolists & dialogs. 162 163 "make nconfig" Enhanced text based color menus. 164 165 "make xconfig" Qt based configuration tool. 166 167 "make gconfig" GTK+ based configuration tool. 168 169 "make oldconfig" Default all questions based on the contents of 170 your existing ./.config file and asking about 171 new config symbols. 172 173 "make silentoldconfig" 174 Like above, but avoids cluttering the screen 175 with questions already answered. 176 Additionally updates the dependencies. 177 178 "make olddefconfig" 179 Like above, but sets new symbols to their default 180 values without prompting. 181 182 "make defconfig" Create a ./.config file by using the default 183 symbol values from either arch/$ARCH/defconfig 184 or arch/$ARCH/configs/${PLATFORM}_defconfig, 185 depending on the architecture. 186 187 "make ${PLATFORM}_defconfig" 188 Create a ./.config file by using the default 189 symbol values from 190 arch/$ARCH/configs/${PLATFORM}_defconfig. 191 Use "make help" to get a list of all available 192 platforms of your architecture. 193 194 "make allyesconfig" 195 Create a ./.config file by setting symbol 196 values to 'y' as much as possible. 197 198 "make allmodconfig" 199 Create a ./.config file by setting symbol 200 values to 'm' as much as possible. 201 202 "make allnoconfig" Create a ./.config file by setting symbol 203 values to 'n' as much as possible. 204 205 "make randconfig" Create a ./.config file by setting symbol 206 values to random values. 207 208 "make localmodconfig" Create a config based on current config and 209 loaded modules (lsmod). Disables any module 210 option that is not needed for the loaded modules. 211 212 To create a localmodconfig for another machine, 213 store the lsmod of that machine into a file 214 and pass it in as a LSMOD parameter. 215 216 target$ lsmod > /tmp/mylsmod 217 target$ scp /tmp/mylsmod host:/tmp 218 219 host$ make LSMOD=/tmp/mylsmod localmodconfig 220 221 The above also works when cross compiling. 222 223 "make localyesconfig" Similar to localmodconfig, except it will convert 224 all module options to built in (=y) options. 225 226 You can find more information on using the Linux kernel config tools 227 in Documentation/kbuild/kconfig.txt. 228 229 - NOTES on ``make config``: 230 231 - Having unnecessary drivers will make the kernel bigger, and can 232 under some circumstances lead to problems: probing for a 233 nonexistent controller card may confuse your other controllers. 234 235 - A kernel with math-emulation compiled in will still use the 236 coprocessor if one is present: the math emulation will just 237 never get used in that case. The kernel will be slightly larger, 238 but will work on different machines regardless of whether they 239 have a math coprocessor or not. 240 241 - The "kernel hacking" configuration details usually result in a 242 bigger or slower kernel (or both), and can even make the kernel 243 less stable by configuring some routines to actively try to 244 break bad code to find kernel problems (kmalloc()). Thus you 245 should probably answer 'n' to the questions for "development", 246 "experimental", or "debugging" features. 247 248Compiling the kernel 249-------------------- 250 251 - Make sure you have at least gcc 3.2 available. 252 For more information, refer to :ref:`Documentation/process/changes.rst <changes>`. 253 254 Please note that you can still run a.out user programs with this kernel. 255 256 - Do a ``make`` to create a compressed kernel image. It is also 257 possible to do ``make install`` if you have lilo installed to suit the 258 kernel makefiles, but you may want to check your particular lilo setup first. 259 260 To do the actual install, you have to be root, but none of the normal 261 build should require that. Don't take the name of root in vain. 262 263 - If you configured any of the parts of the kernel as ``modules``, you 264 will also have to do ``make modules_install``. 265 266 - Verbose kernel compile/build output: 267 268 Normally, the kernel build system runs in a fairly quiet mode (but not 269 totally silent). However, sometimes you or other kernel developers need 270 to see compile, link, or other commands exactly as they are executed. 271 For this, use "verbose" build mode. This is done by passing 272 ``V=1`` to the ``make`` command, e.g.:: 273 274 make V=1 all 275 276 To have the build system also tell the reason for the rebuild of each 277 target, use ``V=2``. The default is ``V=0``. 278 279 - Keep a backup kernel handy in case something goes wrong. This is 280 especially true for the development releases, since each new release 281 contains new code which has not been debugged. Make sure you keep a 282 backup of the modules corresponding to that kernel, as well. If you 283 are installing a new kernel with the same version number as your 284 working kernel, make a backup of your modules directory before you 285 do a ``make modules_install``. 286 287 Alternatively, before compiling, use the kernel config option 288 "LOCALVERSION" to append a unique suffix to the regular kernel version. 289 LOCALVERSION can be set in the "General Setup" menu. 290 291 - In order to boot your new kernel, you'll need to copy the kernel 292 image (e.g. .../linux/arch/x86/boot/bzImage after compilation) 293 to the place where your regular bootable kernel is found. 294 295 - Booting a kernel directly from a floppy without the assistance of a 296 bootloader such as LILO, is no longer supported. 297 298 If you boot Linux from the hard drive, chances are you use LILO, which 299 uses the kernel image as specified in the file /etc/lilo.conf. The 300 kernel image file is usually /vmlinuz, /boot/vmlinuz, /bzImage or 301 /boot/bzImage. To use the new kernel, save a copy of the old image 302 and copy the new image over the old one. Then, you MUST RERUN LILO 303 to update the loading map! If you don't, you won't be able to boot 304 the new kernel image. 305 306 Reinstalling LILO is usually a matter of running /sbin/lilo. 307 You may wish to edit /etc/lilo.conf to specify an entry for your 308 old kernel image (say, /vmlinux.old) in case the new one does not 309 work. See the LILO docs for more information. 310 311 After reinstalling LILO, you should be all set. Shutdown the system, 312 reboot, and enjoy! 313 314 If you ever need to change the default root device, video mode, 315 ramdisk size, etc. in the kernel image, use the ``rdev`` program (or 316 alternatively the LILO boot options when appropriate). No need to 317 recompile the kernel to change these parameters. 318 319 - Reboot with the new kernel and enjoy. 320 321If something goes wrong 322----------------------- 323 324 - If you have problems that seem to be due to kernel bugs, please check 325 the file MAINTAINERS to see if there is a particular person associated 326 with the part of the kernel that you are having trouble with. If there 327 isn't anyone listed there, then the second best thing is to mail 328 them to me (torvalds@linux-foundation.org), and possibly to any other 329 relevant mailing-list or to the newsgroup. 330 331 - In all bug-reports, *please* tell what kernel you are talking about, 332 how to duplicate the problem, and what your setup is (use your common 333 sense). If the problem is new, tell me so, and if the problem is 334 old, please try to tell me when you first noticed it. 335 336 - If the bug results in a message like:: 337 338 unable to handle kernel paging request at address C0000010 339 Oops: 0002 340 EIP: 0010:XXXXXXXX 341 eax: xxxxxxxx ebx: xxxxxxxx ecx: xxxxxxxx edx: xxxxxxxx 342 esi: xxxxxxxx edi: xxxxxxxx ebp: xxxxxxxx 343 ds: xxxx es: xxxx fs: xxxx gs: xxxx 344 Pid: xx, process nr: xx 345 xx xx xx xx xx xx xx xx xx xx 346 347 or similar kernel debugging information on your screen or in your 348 system log, please duplicate it *exactly*. The dump may look 349 incomprehensible to you, but it does contain information that may 350 help debugging the problem. The text above the dump is also 351 important: it tells something about why the kernel dumped code (in 352 the above example, it's due to a bad kernel pointer). More information 353 on making sense of the dump is in Documentation/admin-guide/bug-hunting.rst 354 355 - If you compiled the kernel with CONFIG_KALLSYMS you can send the dump 356 as is, otherwise you will have to use the ``ksymoops`` program to make 357 sense of the dump (but compiling with CONFIG_KALLSYMS is usually preferred). 358 This utility can be downloaded from 359 https://www.kernel.org/pub/linux/utils/kernel/ksymoops/ . 360 Alternatively, you can do the dump lookup by hand: 361 362 - In debugging dumps like the above, it helps enormously if you can 363 look up what the EIP value means. The hex value as such doesn't help 364 me or anybody else very much: it will depend on your particular 365 kernel setup. What you should do is take the hex value from the EIP 366 line (ignore the ``0010:``), and look it up in the kernel namelist to 367 see which kernel function contains the offending address. 368 369 To find out the kernel function name, you'll need to find the system 370 binary associated with the kernel that exhibited the symptom. This is 371 the file 'linux/vmlinux'. To extract the namelist and match it against 372 the EIP from the kernel crash, do:: 373 374 nm vmlinux | sort | less 375 376 This will give you a list of kernel addresses sorted in ascending 377 order, from which it is simple to find the function that contains the 378 offending address. Note that the address given by the kernel 379 debugging messages will not necessarily match exactly with the 380 function addresses (in fact, that is very unlikely), so you can't 381 just 'grep' the list: the list will, however, give you the starting 382 point of each kernel function, so by looking for the function that 383 has a starting address lower than the one you are searching for but 384 is followed by a function with a higher address you will find the one 385 you want. In fact, it may be a good idea to include a bit of 386 "context" in your problem report, giving a few lines around the 387 interesting one. 388 389 If you for some reason cannot do the above (you have a pre-compiled 390 kernel image or similar), telling me as much about your setup as 391 possible will help. Please read the :ref:`admin-guide/reporting-bugs.rst <reportingbugs>` 392 document for details. 393 394 - Alternatively, you can use gdb on a running kernel. (read-only; i.e. you 395 cannot change values or set break points.) To do this, first compile the 396 kernel with -g; edit arch/x86/Makefile appropriately, then do a ``make 397 clean``. You'll also need to enable CONFIG_PROC_FS (via ``make config``). 398 399 After you've rebooted with the new kernel, do ``gdb vmlinux /proc/kcore``. 400 You can now use all the usual gdb commands. The command to look up the 401 point where your system crashed is ``l *0xXXXXXXXX``. (Replace the XXXes 402 with the EIP value.) 403 404 gdb'ing a non-running kernel currently fails because ``gdb`` (wrongly) 405 disregards the starting offset for which the kernel is compiled. 406