1 Linux kernel !! 1 Linux kernel release 4.x <http://kernel.org/>
2 ============ <<
3 2
4 There are several guides for kernel developers !! 3 These are the release notes for Linux version 4. Read them carefully,
5 be rendered in a number of formats, like HTML !! 4 as they tell you what this is all about, explain how to install the
6 Documentation/admin-guide/README.rst first. !! 5 kernel, and what to do if something goes wrong.
7 6
8 In order to build the documentation, use ``mak !! 7 WHAT IS LINUX?
9 ``make pdfdocs``. The formatted documentation <<
10 8
11 https://www.kernel.org/doc/html/latest/ !! 9 Linux is a clone of the operating system Unix, written from scratch by
>> 10 Linus Torvalds with assistance from a loosely-knit team of hackers across
>> 11 the Net. It aims towards POSIX and Single UNIX Specification compliance.
12 12
13 There are various text files in the Documentat !! 13 It has all the features you would expect in a modern fully-fledged Unix,
14 several of them using the reStructuredText mar !! 14 including true multitasking, virtual memory, shared libraries, demand
>> 15 loading, shared copy-on-write executables, proper memory management,
>> 16 and multistack networking including IPv4 and IPv6.
>> 17
>> 18 It is distributed under the GNU General Public License - see the
>> 19 accompanying COPYING file for more details.
>> 20
>> 21 ON WHAT HARDWARE DOES IT RUN?
>> 22
>> 23 Although originally developed first for 32-bit x86-based PCs (386 or higher),
>> 24 today Linux also runs on (at least) the Compaq Alpha AXP, Sun SPARC and
>> 25 UltraSPARC, Motorola 68000, PowerPC, PowerPC64, ARM, Hitachi SuperH, Cell,
>> 26 IBM S/390, MIPS, HP PA-RISC, Intel IA-64, DEC VAX, AMD x86-64, AXIS CRIS,
>> 27 Xtensa, Tilera TILE, AVR32, ARC and Renesas M32R architectures.
>> 28
>> 29 Linux is easily portable to most general-purpose 32- or 64-bit architectures
>> 30 as long as they have a paged memory management unit (PMMU) and a port of the
>> 31 GNU C compiler (gcc) (part of The GNU Compiler Collection, GCC). Linux has
>> 32 also been ported to a number of architectures without a PMMU, although
>> 33 functionality is then obviously somewhat limited.
>> 34 Linux has also been ported to itself. You can now run the kernel as a
>> 35 userspace application - this is called UserMode Linux (UML).
>> 36
>> 37 DOCUMENTATION:
>> 38
>> 39 - There is a lot of documentation available both in electronic form on
>> 40 the Internet and in books, both Linux-specific and pertaining to
>> 41 general UNIX questions. I'd recommend looking into the documentation
>> 42 subdirectories on any Linux FTP site for the LDP (Linux Documentation
>> 43 Project) books. This README is not meant to be documentation on the
>> 44 system: there are much better sources available.
>> 45
>> 46 - There are various README files in the Documentation/ subdirectory:
>> 47 these typically contain kernel-specific installation notes for some
>> 48 drivers for example. See Documentation/00-INDEX for a list of what
>> 49 is contained in each file. Please read the Changes file, as it
>> 50 contains information about the problems, which may result by upgrading
>> 51 your kernel.
>> 52
>> 53 - The Documentation/DocBook/ subdirectory contains several guides for
>> 54 kernel developers and users. These guides can be rendered in a
>> 55 number of formats: PostScript (.ps), PDF, HTML, & man-pages, among others.
>> 56 After installation, "make psdocs", "make pdfdocs", "make htmldocs",
>> 57 or "make mandocs" will render the documentation in the requested format.
>> 58
>> 59 INSTALLING the kernel source:
>> 60
>> 61 - If you install the full sources, put the kernel tarball in a
>> 62 directory where you have permissions (eg. 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 Documentation/applying-patches.txt
>> 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
>> 113 SOFTWARE REQUIREMENTS
>> 114
>> 115 Compiling and running the 4.x kernels requires up-to-date
>> 116 versions of various software packages. Consult
>> 117 Documentation/Changes for the minimum version numbers required
>> 118 and how to get updates for these packages. Beware that using
>> 119 excessively old versions of these packages can cause indirect
>> 120 errors that are very difficult to track down, so don't assume that
>> 121 you can just update packages when obvious problems arise during
>> 122 build or operation.
>> 123
>> 124 BUILD directory for the kernel:
>> 125
>> 126 When compiling the kernel, all output files will per default be
>> 127 stored together with the kernel source code.
>> 128 Using the option "make O=output/dir" allow you to specify an alternate
>> 129 place for the output files (including .config).
>> 130 Example:
>> 131
>> 132 kernel source code: /usr/src/linux-4.X
>> 133 build directory: /home/name/build/kernel
>> 134
>> 135 To configure and build the kernel, use:
>> 136
>> 137 cd /usr/src/linux-4.X
>> 138 make O=/home/name/build/kernel menuconfig
>> 139 make O=/home/name/build/kernel
>> 140 sudo make O=/home/name/build/kernel modules_install install
>> 141
>> 142 Please note: If the 'O=output/dir' option is used, then it must be
>> 143 used for all invocations of make.
>> 144
>> 145 CONFIGURING the kernel:
>> 146
>> 147 Do not skip this step even if you are only upgrading one minor
>> 148 version. New configuration options are added in each release, and
>> 149 odd problems will turn up if the configuration files are not set up
>> 150 as expected. If you want to carry your existing configuration to a
>> 151 new version with minimal work, use "make oldconfig", which will
>> 152 only ask you for the answers to new questions.
>> 153
>> 154 - Alternative configuration commands are:
>> 155
>> 156 "make config" Plain text interface.
>> 157
>> 158 "make menuconfig" Text based color menus, radiolists & dialogs.
>> 159
>> 160 "make nconfig" Enhanced text based color menus.
>> 161
>> 162 "make xconfig" X windows (Qt) based configuration tool.
>> 163
>> 164 "make gconfig" X windows (GTK+) based configuration tool.
>> 165
>> 166 "make oldconfig" Default all questions based on the contents of
>> 167 your existing ./.config file and asking about
>> 168 new config symbols.
>> 169
>> 170 "make silentoldconfig"
>> 171 Like above, but avoids cluttering the screen
>> 172 with questions already answered.
>> 173 Additionally updates the dependencies.
>> 174
>> 175 "make olddefconfig"
>> 176 Like above, but sets new symbols to their default
>> 177 values without prompting.
>> 178
>> 179 "make defconfig" Create a ./.config file by using the default
>> 180 symbol values from either arch/$ARCH/defconfig
>> 181 or arch/$ARCH/configs/${PLATFORM}_defconfig,
>> 182 depending on the architecture.
>> 183
>> 184 "make ${PLATFORM}_defconfig"
>> 185 Create a ./.config file by using the default
>> 186 symbol values from
>> 187 arch/$ARCH/configs/${PLATFORM}_defconfig.
>> 188 Use "make help" to get a list of all available
>> 189 platforms of your architecture.
>> 190
>> 191 "make allyesconfig"
>> 192 Create a ./.config file by setting symbol
>> 193 values to 'y' as much as possible.
>> 194
>> 195 "make allmodconfig"
>> 196 Create a ./.config file by setting symbol
>> 197 values to 'm' as much as possible.
>> 198
>> 199 "make allnoconfig" Create a ./.config file by setting symbol
>> 200 values to 'n' as much as possible.
>> 201
>> 202 "make randconfig" Create a ./.config file by setting symbol
>> 203 values to random values.
>> 204
>> 205 "make localmodconfig" Create a config based on current config and
>> 206 loaded modules (lsmod). Disables any module
>> 207 option that is not needed for the loaded modules.
>> 208
>> 209 To create a localmodconfig for another machine,
>> 210 store the lsmod of that machine into a file
>> 211 and pass it in as a LSMOD parameter.
>> 212
>> 213 target$ lsmod > /tmp/mylsmod
>> 214 target$ scp /tmp/mylsmod host:/tmp
>> 215
>> 216 host$ make LSMOD=/tmp/mylsmod localmodconfig
>> 217
>> 218 The above also works when cross compiling.
>> 219
>> 220 "make localyesconfig" Similar to localmodconfig, except it will convert
>> 221 all module options to built in (=y) options.
>> 222
>> 223 You can find more information on using the Linux kernel config tools
>> 224 in Documentation/kbuild/kconfig.txt.
>> 225
>> 226 - NOTES on "make config":
>> 227
>> 228 - Having unnecessary drivers will make the kernel bigger, and can
>> 229 under some circumstances lead to problems: probing for a
>> 230 nonexistent controller card may confuse your other controllers
>> 231
>> 232 - Compiling the kernel with "Processor type" set higher than 386
>> 233 will result in a kernel that does NOT work on a 386. The
>> 234 kernel will detect this on bootup, and give up.
>> 235
>> 236 - A kernel with math-emulation compiled in will still use the
>> 237 coprocessor if one is present: the math emulation will just
>> 238 never get used in that case. The kernel will be slightly larger,
>> 239 but will work on different machines regardless of whether they
>> 240 have a math coprocessor or not.
>> 241
>> 242 - The "kernel hacking" configuration details usually result in a
>> 243 bigger or slower kernel (or both), and can even make the kernel
>> 244 less stable by configuring some routines to actively try to
>> 245 break bad code to find kernel problems (kmalloc()). Thus you
>> 246 should probably answer 'n' to the questions for "development",
>> 247 "experimental", or "debugging" features.
>> 248
>> 249 COMPILING the kernel:
>> 250
>> 251 - Make sure you have at least gcc 3.2 available.
>> 252 For more information, refer to Documentation/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 inserting
>> 272 "V=1" in 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/i386/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
>> 321 IF SOMETHING GOES WRONG:
>> 322
>> 323 - If you have problems that seem to be due to kernel bugs, please check
>> 324 the file MAINTAINERS to see if there is a particular person associated
>> 325 with the part of the kernel that you are having trouble with. If there
>> 326 isn't anyone listed there, then the second best thing is to mail
>> 327 them to me (torvalds@linux-foundation.org), and possibly to any other
>> 328 relevant mailing-list or to the newsgroup.
>> 329
>> 330 - In all bug-reports, *please* tell what kernel you are talking about,
>> 331 how to duplicate the problem, and what your setup is (use your common
>> 332 sense). If the problem is new, tell me so, and if the problem is
>> 333 old, please try to tell me when you first noticed it.
>> 334
>> 335 - If the bug results in a message like
>> 336
>> 337 unable to handle kernel paging request at address C0000010
>> 338 Oops: 0002
>> 339 EIP: 0010:XXXXXXXX
>> 340 eax: xxxxxxxx ebx: xxxxxxxx ecx: xxxxxxxx edx: xxxxxxxx
>> 341 esi: xxxxxxxx edi: xxxxxxxx ebp: xxxxxxxx
>> 342 ds: xxxx es: xxxx fs: xxxx gs: xxxx
>> 343 Pid: xx, process nr: xx
>> 344 xx xx xx xx xx xx xx xx xx xx
>> 345
>> 346 or similar kernel debugging information on your screen or in your
>> 347 system log, please duplicate it *exactly*. The dump may look
>> 348 incomprehensible to you, but it does contain information that may
>> 349 help debugging the problem. The text above the dump is also
>> 350 important: it tells something about why the kernel dumped code (in
>> 351 the above example, it's due to a bad kernel pointer). More information
>> 352 on making sense of the dump is in Documentation/oops-tracing.txt
>> 353
>> 354 - If you compiled the kernel with CONFIG_KALLSYMS you can send the dump
>> 355 as is, otherwise you will have to use the "ksymoops" program to make
>> 356 sense of the dump (but compiling with CONFIG_KALLSYMS is usually preferred).
>> 357 This utility can be downloaded from
>> 358 ftp://ftp.<country>.kernel.org/pub/linux/utils/kernel/ksymoops/ .
>> 359 Alternatively, you can do the dump lookup by hand:
>> 360
>> 361 - In debugging dumps like the above, it helps enormously if you can
>> 362 look up what the EIP value means. The hex value as such doesn't help
>> 363 me or anybody else very much: it will depend on your particular
>> 364 kernel setup. What you should do is take the hex value from the EIP
>> 365 line (ignore the "0010:"), and look it up in the kernel namelist to
>> 366 see which kernel function contains the offending address.
>> 367
>> 368 To find out the kernel function name, you'll need to find the system
>> 369 binary associated with the kernel that exhibited the symptom. This is
>> 370 the file 'linux/vmlinux'. To extract the namelist and match it against
>> 371 the EIP from the kernel crash, do:
>> 372
>> 373 nm vmlinux | sort | less
>> 374
>> 375 This will give you a list of kernel addresses sorted in ascending
>> 376 order, from which it is simple to find the function that contains the
>> 377 offending address. Note that the address given by the kernel
>> 378 debugging messages will not necessarily match exactly with the
>> 379 function addresses (in fact, that is very unlikely), so you can't
>> 380 just 'grep' the list: the list will, however, give you the starting
>> 381 point of each kernel function, so by looking for the function that
>> 382 has a starting address lower than the one you are searching for but
>> 383 is followed by a function with a higher address you will find the one
>> 384 you want. In fact, it may be a good idea to include a bit of
>> 385 "context" in your problem report, giving a few lines around the
>> 386 interesting one.
>> 387
>> 388 If you for some reason cannot do the above (you have a pre-compiled
>> 389 kernel image or similar), telling me as much about your setup as
>> 390 possible will help. Please read the REPORTING-BUGS document for details.
>> 391
>> 392 - Alternatively, you can use gdb on a running kernel. (read-only; i.e. you
>> 393 cannot change values or set break points.) To do this, first compile the
>> 394 kernel with -g; edit arch/i386/Makefile appropriately, then do a "make
>> 395 clean". You'll also need to enable CONFIG_PROC_FS (via "make config").
>> 396
>> 397 After you've rebooted with the new kernel, do "gdb vmlinux /proc/kcore".
>> 398 You can now use all the usual gdb commands. The command to look up the
>> 399 point where your system crashed is "l *0xXXXXXXXX". (Replace the XXXes
>> 400 with the EIP value.)
>> 401
>> 402 gdb'ing a non-running kernel currently fails because gdb (wrongly)
>> 403 disregards the starting offset for which the kernel is compiled.
15 404
16 Please read the Documentation/process/changes. <<
17 requirements for building and running the kern <<
18 the problems which may result by upgrading you <<
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