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 58 - The Documentation/DocBook/ subdirectory contains several guides for 59 kernel developers and users. These guides can be rendered in a 60 number of formats: PostScript (.ps), PDF, HTML, & man-pages, among others. 61 After installation, ``make psdocs``, ``make pdfdocs``, ``make htmldocs``, 62 or ``make mandocs`` will render the documentation in the requested format. 63 64Installing the kernel source 65---------------------------- 66 67 - If you install the full sources, put the kernel tarball in a 68 directory where you have permissions (e.g. your home directory) and 69 unpack it:: 70 71 xz -cd linux-4.X.tar.xz | tar xvf - 72 73 Replace "X" with the version number of the latest kernel. 74 75 Do NOT use the /usr/src/linux area! This area has a (usually 76 incomplete) set of kernel headers that are used by the library header 77 files. They should match the library, and not get messed up by 78 whatever the kernel-du-jour happens to be. 79 80 - You can also upgrade between 4.x releases by patching. Patches are 81 distributed in the xz format. To install by patching, get all the 82 newer patch files, enter the top level directory of the kernel source 83 (linux-4.X) and execute:: 84 85 xz -cd ../patch-4.x.xz | patch -p1 86 87 Replace "x" for all versions bigger than the version "X" of your current 88 source tree, **in_order**, and you should be ok. You may want to remove 89 the backup files (some-file-name~ or some-file-name.orig), and make sure 90 that there are no failed patches (some-file-name# or some-file-name.rej). 91 If there are, either you or I have made a mistake. 92 93 Unlike patches for the 4.x kernels, patches for the 4.x.y kernels 94 (also known as the -stable kernels) are not incremental but instead apply 95 directly to the base 4.x kernel. For example, if your base kernel is 4.0 96 and you want to apply the 4.0.3 patch, you must not first apply the 4.0.1 97 and 4.0.2 patches. Similarly, if you are running kernel version 4.0.2 and 98 want to jump to 4.0.3, you must first reverse the 4.0.2 patch (that is, 99 patch -R) **before** applying the 4.0.3 patch. You can read more on this in 100 :ref:`Documentation/process/applying-patches.rst <applying_patches>`. 101 102 Alternatively, the script patch-kernel can be used to automate this 103 process. It determines the current kernel version and applies any 104 patches found:: 105 106 linux/scripts/patch-kernel linux 107 108 The first argument in the command above is the location of the 109 kernel source. Patches are applied from the current directory, but 110 an alternative directory can be specified as the second argument. 111 112 - Make sure you have no stale .o files and dependencies lying around:: 113 114 cd linux 115 make mrproper 116 117 You should now have the sources correctly installed. 118 119Software requirements 120--------------------- 121 122 Compiling and running the 4.x kernels requires up-to-date 123 versions of various software packages. Consult 124 :ref:`Documentation/process/changes.rst <changes>` for the minimum version numbers 125 required and how to get updates for these packages. Beware that using 126 excessively old versions of these packages can cause indirect 127 errors that are very difficult to track down, so don't assume that 128 you can just update packages when obvious problems arise during 129 build or operation. 130 131Build directory for the kernel 132------------------------------ 133 134 When compiling the kernel, all output files will per default be 135 stored together with the kernel source code. 136 Using the option ``make O=output/dir`` allows you to specify an alternate 137 place for the output files (including .config). 138 Example:: 139 140 kernel source code: /usr/src/linux-4.X 141 build directory: /home/name/build/kernel 142 143 To configure and build the kernel, use:: 144 145 cd /usr/src/linux-4.X 146 make O=/home/name/build/kernel menuconfig 147 make O=/home/name/build/kernel 148 sudo make O=/home/name/build/kernel modules_install install 149 150 Please note: If the ``O=output/dir`` option is used, then it must be 151 used for all invocations of make. 152 153Configuring the kernel 154---------------------- 155 156 Do not skip this step even if you are only upgrading one minor 157 version. New configuration options are added in each release, and 158 odd problems will turn up if the configuration files are not set up 159 as expected. If you want to carry your existing configuration to a 160 new version with minimal work, use ``make oldconfig``, which will 161 only ask you for the answers to new questions. 162 163 - Alternative configuration commands are:: 164 165 "make config" Plain text interface. 166 167 "make menuconfig" Text based color menus, radiolists & dialogs. 168 169 "make nconfig" Enhanced text based color menus. 170 171 "make xconfig" Qt based configuration tool. 172 173 "make gconfig" GTK+ based configuration tool. 174 175 "make oldconfig" Default all questions based on the contents of 176 your existing ./.config file and asking about 177 new config symbols. 178 179 "make silentoldconfig" 180 Like above, but avoids cluttering the screen 181 with questions already answered. 182 Additionally updates the dependencies. 183 184 "make olddefconfig" 185 Like above, but sets new symbols to their default 186 values without prompting. 187 188 "make defconfig" Create a ./.config file by using the default 189 symbol values from either arch/$ARCH/defconfig 190 or arch/$ARCH/configs/${PLATFORM}_defconfig, 191 depending on the architecture. 192 193 "make ${PLATFORM}_defconfig" 194 Create a ./.config file by using the default 195 symbol values from 196 arch/$ARCH/configs/${PLATFORM}_defconfig. 197 Use "make help" to get a list of all available 198 platforms of your architecture. 199 200 "make allyesconfig" 201 Create a ./.config file by setting symbol 202 values to 'y' as much as possible. 203 204 "make allmodconfig" 205 Create a ./.config file by setting symbol 206 values to 'm' as much as possible. 207 208 "make allnoconfig" Create a ./.config file by setting symbol 209 values to 'n' as much as possible. 210 211 "make randconfig" Create a ./.config file by setting symbol 212 values to random values. 213 214 "make localmodconfig" Create a config based on current config and 215 loaded modules (lsmod). Disables any module 216 option that is not needed for the loaded modules. 217 218 To create a localmodconfig for another machine, 219 store the lsmod of that machine into a file 220 and pass it in as a LSMOD parameter. 221 222 target$ lsmod > /tmp/mylsmod 223 target$ scp /tmp/mylsmod host:/tmp 224 225 host$ make LSMOD=/tmp/mylsmod localmodconfig 226 227 The above also works when cross compiling. 228 229 "make localyesconfig" Similar to localmodconfig, except it will convert 230 all module options to built in (=y) options. 231 232 You can find more information on using the Linux kernel config tools 233 in Documentation/kbuild/kconfig.txt. 234 235 - NOTES on ``make config``: 236 237 - Having unnecessary drivers will make the kernel bigger, and can 238 under some circumstances lead to problems: probing for a 239 nonexistent controller card may confuse your other controllers. 240 241 - A kernel with math-emulation compiled in will still use the 242 coprocessor if one is present: the math emulation will just 243 never get used in that case. The kernel will be slightly larger, 244 but will work on different machines regardless of whether they 245 have a math coprocessor or not. 246 247 - The "kernel hacking" configuration details usually result in a 248 bigger or slower kernel (or both), and can even make the kernel 249 less stable by configuring some routines to actively try to 250 break bad code to find kernel problems (kmalloc()). Thus you 251 should probably answer 'n' to the questions for "development", 252 "experimental", or "debugging" features. 253 254Compiling the kernel 255-------------------- 256 257 - Make sure you have at least gcc 3.2 available. 258 For more information, refer to :ref:`Documentation/process/changes.rst <changes>`. 259 260 Please note that you can still run a.out user programs with this kernel. 261 262 - Do a ``make`` to create a compressed kernel image. It is also 263 possible to do ``make install`` if you have lilo installed to suit the 264 kernel makefiles, but you may want to check your particular lilo setup first. 265 266 To do the actual install, you have to be root, but none of the normal 267 build should require that. Don't take the name of root in vain. 268 269 - If you configured any of the parts of the kernel as ``modules``, you 270 will also have to do ``make modules_install``. 271 272 - Verbose kernel compile/build output: 273 274 Normally, the kernel build system runs in a fairly quiet mode (but not 275 totally silent). However, sometimes you or other kernel developers need 276 to see compile, link, or other commands exactly as they are executed. 277 For this, use "verbose" build mode. This is done by passing 278 ``V=1`` to the ``make`` command, e.g.:: 279 280 make V=1 all 281 282 To have the build system also tell the reason for the rebuild of each 283 target, use ``V=2``. The default is ``V=0``. 284 285 - Keep a backup kernel handy in case something goes wrong. This is 286 especially true for the development releases, since each new release 287 contains new code which has not been debugged. Make sure you keep a 288 backup of the modules corresponding to that kernel, as well. If you 289 are installing a new kernel with the same version number as your 290 working kernel, make a backup of your modules directory before you 291 do a ``make modules_install``. 292 293 Alternatively, before compiling, use the kernel config option 294 "LOCALVERSION" to append a unique suffix to the regular kernel version. 295 LOCALVERSION can be set in the "General Setup" menu. 296 297 - In order to boot your new kernel, you'll need to copy the kernel 298 image (e.g. .../linux/arch/x86/boot/bzImage after compilation) 299 to the place where your regular bootable kernel is found. 300 301 - Booting a kernel directly from a floppy without the assistance of a 302 bootloader such as LILO, is no longer supported. 303 304 If you boot Linux from the hard drive, chances are you use LILO, which 305 uses the kernel image as specified in the file /etc/lilo.conf. The 306 kernel image file is usually /vmlinuz, /boot/vmlinuz, /bzImage or 307 /boot/bzImage. To use the new kernel, save a copy of the old image 308 and copy the new image over the old one. Then, you MUST RERUN LILO 309 to update the loading map! If you don't, you won't be able to boot 310 the new kernel image. 311 312 Reinstalling LILO is usually a matter of running /sbin/lilo. 313 You may wish to edit /etc/lilo.conf to specify an entry for your 314 old kernel image (say, /vmlinux.old) in case the new one does not 315 work. See the LILO docs for more information. 316 317 After reinstalling LILO, you should be all set. Shutdown the system, 318 reboot, and enjoy! 319 320 If you ever need to change the default root device, video mode, 321 ramdisk size, etc. in the kernel image, use the ``rdev`` program (or 322 alternatively the LILO boot options when appropriate). No need to 323 recompile the kernel to change these parameters. 324 325 - Reboot with the new kernel and enjoy. 326 327If something goes wrong 328----------------------- 329 330 - If you have problems that seem to be due to kernel bugs, please check 331 the file MAINTAINERS to see if there is a particular person associated 332 with the part of the kernel that you are having trouble with. If there 333 isn't anyone listed there, then the second best thing is to mail 334 them to me (torvalds@linux-foundation.org), and possibly to any other 335 relevant mailing-list or to the newsgroup. 336 337 - In all bug-reports, *please* tell what kernel you are talking about, 338 how to duplicate the problem, and what your setup is (use your common 339 sense). If the problem is new, tell me so, and if the problem is 340 old, please try to tell me when you first noticed it. 341 342 - If the bug results in a message like:: 343 344 unable to handle kernel paging request at address C0000010 345 Oops: 0002 346 EIP: 0010:XXXXXXXX 347 eax: xxxxxxxx ebx: xxxxxxxx ecx: xxxxxxxx edx: xxxxxxxx 348 esi: xxxxxxxx edi: xxxxxxxx ebp: xxxxxxxx 349 ds: xxxx es: xxxx fs: xxxx gs: xxxx 350 Pid: xx, process nr: xx 351 xx xx xx xx xx xx xx xx xx xx 352 353 or similar kernel debugging information on your screen or in your 354 system log, please duplicate it *exactly*. The dump may look 355 incomprehensible to you, but it does contain information that may 356 help debugging the problem. The text above the dump is also 357 important: it tells something about why the kernel dumped code (in 358 the above example, it's due to a bad kernel pointer). More information 359 on making sense of the dump is in Documentation/admin-guide/oops-tracing.rst 360 361 - If you compiled the kernel with CONFIG_KALLSYMS you can send the dump 362 as is, otherwise you will have to use the ``ksymoops`` program to make 363 sense of the dump (but compiling with CONFIG_KALLSYMS is usually preferred). 364 This utility can be downloaded from 365 ftp://ftp.<country>.kernel.org/pub/linux/utils/kernel/ksymoops/ . 366 Alternatively, you can do the dump lookup by hand: 367 368 - In debugging dumps like the above, it helps enormously if you can 369 look up what the EIP value means. The hex value as such doesn't help 370 me or anybody else very much: it will depend on your particular 371 kernel setup. What you should do is take the hex value from the EIP 372 line (ignore the ``0010:``), and look it up in the kernel namelist to 373 see which kernel function contains the offending address. 374 375 To find out the kernel function name, you'll need to find the system 376 binary associated with the kernel that exhibited the symptom. This is 377 the file 'linux/vmlinux'. To extract the namelist and match it against 378 the EIP from the kernel crash, do:: 379 380 nm vmlinux | sort | less 381 382 This will give you a list of kernel addresses sorted in ascending 383 order, from which it is simple to find the function that contains the 384 offending address. Note that the address given by the kernel 385 debugging messages will not necessarily match exactly with the 386 function addresses (in fact, that is very unlikely), so you can't 387 just 'grep' the list: the list will, however, give you the starting 388 point of each kernel function, so by looking for the function that 389 has a starting address lower than the one you are searching for but 390 is followed by a function with a higher address you will find the one 391 you want. In fact, it may be a good idea to include a bit of 392 "context" in your problem report, giving a few lines around the 393 interesting one. 394 395 If you for some reason cannot do the above (you have a pre-compiled 396 kernel image or similar), telling me as much about your setup as 397 possible will help. Please read the :ref:`admin-guide/reporting-bugs.rst <reportingbugs>` 398 document for details. 399 400 - Alternatively, you can use gdb on a running kernel. (read-only; i.e. you 401 cannot change values or set break points.) To do this, first compile the 402 kernel with -g; edit arch/x86/Makefile appropriately, then do a ``make 403 clean``. You'll also need to enable CONFIG_PROC_FS (via ``make config``). 404 405 After you've rebooted with the new kernel, do ``gdb vmlinux /proc/kcore``. 406 You can now use all the usual gdb commands. The command to look up the 407 point where your system crashed is ``l *0xXXXXXXXX``. (Replace the XXXes 408 with the EIP value.) 409 410 gdb'ing a non-running kernel currently fails because ``gdb`` (wrongly) 411 disregards the starting offset for which the kernel is compiled. 412