1 Linux kernel !! 1 Linux kernel release 3.x <http://kernel.org/>
2 ============ <<
3 2
4 There are several guides for kernel developers !! 3 These are the release notes for Linux version 3. 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 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 gzip -cd linux-3.X.tar.gz | tar xvf -
>> 66
>> 67 or
>> 68
>> 69 bzip2 -dc linux-3.X.tar.bz2 | tar xvf -
>> 70
>> 71 Replace "X" with the version number of the latest kernel.
>> 72
>> 73 Do NOT use the /usr/src/linux area! This area has a (usually
>> 74 incomplete) set of kernel headers that are used by the library header
>> 75 files. They should match the library, and not get messed up by
>> 76 whatever the kernel-du-jour happens to be.
>> 77
>> 78 - You can also upgrade between 3.x releases by patching. Patches are
>> 79 distributed in the traditional gzip and the newer bzip2 format. To
>> 80 install by patching, get all the newer patch files, enter the
>> 81 top level directory of the kernel source (linux-3.X) and execute:
>> 82
>> 83 gzip -cd ../patch-3.x.gz | patch -p1
>> 84
>> 85 or
>> 86
>> 87 bzip2 -dc ../patch-3.x.bz2 | patch -p1
>> 88
>> 89 Replace "x" for all versions bigger than the version "X" of your current
>> 90 source tree, _in_order_, and you should be ok. You may want to remove
>> 91 the backup files (some-file-name~ or some-file-name.orig), and make sure
>> 92 that there are no failed patches (some-file-name# or some-file-name.rej).
>> 93 If there are, either you or I have made a mistake.
>> 94
>> 95 Unlike patches for the 3.x kernels, patches for the 3.x.y kernels
>> 96 (also known as the -stable kernels) are not incremental but instead apply
>> 97 directly to the base 3.x kernel. For example, if your base kernel is 3.0
>> 98 and you want to apply the 3.0.3 patch, you must not first apply the 3.0.1
>> 99 and 3.0.2 patches. Similarly, if you are running kernel version 3.0.2 and
>> 100 want to jump to 3.0.3, you must first reverse the 3.0.2 patch (that is,
>> 101 patch -R) _before_ applying the 3.0.3 patch. You can read more on this in
>> 102 Documentation/applying-patches.txt
>> 103
>> 104 Alternatively, the script patch-kernel can be used to automate this
>> 105 process. It determines the current kernel version and applies any
>> 106 patches found.
>> 107
>> 108 linux/scripts/patch-kernel linux
>> 109
>> 110 The first argument in the command above is the location of the
>> 111 kernel source. Patches are applied from the current directory, but
>> 112 an alternative directory can be specified as the second argument.
>> 113
>> 114 - Make sure you have no stale .o files and dependencies lying around:
>> 115
>> 116 cd linux
>> 117 make mrproper
>> 118
>> 119 You should now have the sources correctly installed.
>> 120
>> 121 SOFTWARE REQUIREMENTS
>> 122
>> 123 Compiling and running the 3.x kernels requires up-to-date
>> 124 versions of various software packages. Consult
>> 125 Documentation/Changes for the minimum version numbers required
>> 126 and how to get updates for these packages. Beware that using
>> 127 excessively old versions of these packages can cause indirect
>> 128 errors that are very difficult to track down, so don't assume that
>> 129 you can just update packages when obvious problems arise during
>> 130 build or operation.
>> 131
>> 132 BUILD directory for the kernel:
>> 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" allow you to specify an alternate
>> 137 place for the output files (including .config).
>> 138 Example:
>> 139
>> 140 kernel source code: /usr/src/linux-3.X
>> 141 build directory: /home/name/build/kernel
>> 142
>> 143 To configure and build the kernel, use:
>> 144
>> 145 cd /usr/src/linux-3.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
>> 153 CONFIGURING the kernel:
>> 154
>> 155 Do not skip this step even if you are only upgrading one minor
>> 156 version. New configuration options are added in each release, and
>> 157 odd problems will turn up if the configuration files are not set up
>> 158 as expected. If you want to carry your existing configuration to a
>> 159 new version with minimal work, use "make oldconfig", which will
>> 160 only ask you for the answers to new questions.
>> 161
>> 162 - Alternative configuration commands are:
>> 163
>> 164 "make config" Plain text interface.
>> 165
>> 166 "make menuconfig" Text based color menus, radiolists & dialogs.
>> 167
>> 168 "make nconfig" Enhanced text based color menus.
>> 169
>> 170 "make xconfig" X windows (Qt) based configuration tool.
>> 171
>> 172 "make gconfig" X windows (Gtk) based configuration tool.
>> 173
>> 174 "make oldconfig" Default all questions based on the contents of
>> 175 your existing ./.config file and asking about
>> 176 new config symbols.
>> 177
>> 178 "make silentoldconfig"
>> 179 Like above, but avoids cluttering the screen
>> 180 with questions already answered.
>> 181 Additionally updates the dependencies.
>> 182
>> 183 "make olddefconfig"
>> 184 Like above, but sets new symbols to their default
>> 185 values without prompting.
>> 186
>> 187 "make defconfig" Create a ./.config file by using the default
>> 188 symbol values from either arch/$ARCH/defconfig
>> 189 or arch/$ARCH/configs/${PLATFORM}_defconfig,
>> 190 depending on the architecture.
>> 191
>> 192 "make ${PLATFORM}_defconfig"
>> 193 Create a ./.config file by using the default
>> 194 symbol values from
>> 195 arch/$ARCH/configs/${PLATFORM}_defconfig.
>> 196 Use "make help" to get a list of all available
>> 197 platforms of your architecture.
>> 198
>> 199 "make allyesconfig"
>> 200 Create a ./.config file by setting symbol
>> 201 values to 'y' as much as possible.
>> 202
>> 203 "make allmodconfig"
>> 204 Create a ./.config file by setting symbol
>> 205 values to 'm' as much as possible.
>> 206
>> 207 "make allnoconfig" Create a ./.config file by setting symbol
>> 208 values to 'n' as much as possible.
>> 209
>> 210 "make randconfig" Create a ./.config file by setting symbol
>> 211 values to random values.
>> 212
>> 213 "make localmodconfig" Create a config based on current config and
>> 214 loaded modules (lsmod). Disables any module
>> 215 option that is not needed for the loaded modules.
>> 216
>> 217 To create a localmodconfig for another machine,
>> 218 store the lsmod of that machine into a file
>> 219 and pass it in as a LSMOD parameter.
>> 220
>> 221 target$ lsmod > /tmp/mylsmod
>> 222 target$ scp /tmp/mylsmod host:/tmp
>> 223
>> 224 host$ make LSMOD=/tmp/mylsmod localmodconfig
>> 225
>> 226 The above also works when cross compiling.
>> 227
>> 228 "make localyesconfig" Similar to localmodconfig, except it will convert
>> 229 all module options to built in (=y) options.
>> 230
>> 231 You can find more information on using the Linux kernel config tools
>> 232 in Documentation/kbuild/kconfig.txt.
>> 233
>> 234 - NOTES on "make config":
>> 235
>> 236 - Having unnecessary drivers will make the kernel bigger, and can
>> 237 under some circumstances lead to problems: probing for a
>> 238 nonexistent controller card may confuse your other controllers
>> 239
>> 240 - Compiling the kernel with "Processor type" set higher than 386
>> 241 will result in a kernel that does NOT work on a 386. The
>> 242 kernel will detect this on bootup, and give up.
>> 243
>> 244 - A kernel with math-emulation compiled in will still use the
>> 245 coprocessor if one is present: the math emulation will just
>> 246 never get used in that case. The kernel will be slightly larger,
>> 247 but will work on different machines regardless of whether they
>> 248 have a math coprocessor or not.
>> 249
>> 250 - The "kernel hacking" configuration details usually result in a
>> 251 bigger or slower kernel (or both), and can even make the kernel
>> 252 less stable by configuring some routines to actively try to
>> 253 break bad code to find kernel problems (kmalloc()). Thus you
>> 254 should probably answer 'n' to the questions for "development",
>> 255 "experimental", or "debugging" features.
>> 256
>> 257 COMPILING the kernel:
>> 258
>> 259 - Make sure you have at least gcc 3.2 available.
>> 260 For more information, refer to Documentation/Changes.
>> 261
>> 262 Please note that you can still run a.out user programs with this kernel.
>> 263
>> 264 - Do a "make" to create a compressed kernel image. It is also
>> 265 possible to do "make install" if you have lilo installed to suit the
>> 266 kernel makefiles, but you may want to check your particular lilo setup first.
>> 267
>> 268 To do the actual install, you have to be root, but none of the normal
>> 269 build should require that. Don't take the name of root in vain.
>> 270
>> 271 - If you configured any of the parts of the kernel as `modules', you
>> 272 will also have to do "make modules_install".
>> 273
>> 274 - Verbose kernel compile/build output:
>> 275
>> 276 Normally, the kernel build system runs in a fairly quiet mode (but not
>> 277 totally silent). However, sometimes you or other kernel developers need
>> 278 to see compile, link, or other commands exactly as they are executed.
>> 279 For this, use "verbose" build mode. This is done by inserting
>> 280 "V=1" in the "make" command. E.g.:
>> 281
>> 282 make V=1 all
>> 283
>> 284 To have the build system also tell the reason for the rebuild of each
>> 285 target, use "V=2". The default is "V=0".
>> 286
>> 287 - Keep a backup kernel handy in case something goes wrong. This is
>> 288 especially true for the development releases, since each new release
>> 289 contains new code which has not been debugged. Make sure you keep a
>> 290 backup of the modules corresponding to that kernel, as well. If you
>> 291 are installing a new kernel with the same version number as your
>> 292 working kernel, make a backup of your modules directory before you
>> 293 do a "make modules_install".
>> 294
>> 295 Alternatively, before compiling, use the kernel config option
>> 296 "LOCALVERSION" to append a unique suffix to the regular kernel version.
>> 297 LOCALVERSION can be set in the "General Setup" menu.
>> 298
>> 299 - In order to boot your new kernel, you'll need to copy the kernel
>> 300 image (e.g. .../linux/arch/i386/boot/bzImage after compilation)
>> 301 to the place where your regular bootable kernel is found.
>> 302
>> 303 - Booting a kernel directly from a floppy without the assistance of a
>> 304 bootloader such as LILO, is no longer supported.
>> 305
>> 306 If you boot Linux from the hard drive, chances are you use LILO, which
>> 307 uses the kernel image as specified in the file /etc/lilo.conf. The
>> 308 kernel image file is usually /vmlinuz, /boot/vmlinuz, /bzImage or
>> 309 /boot/bzImage. To use the new kernel, save a copy of the old image
>> 310 and copy the new image over the old one. Then, you MUST RERUN LILO
>> 311 to update the loading map!! If you don't, you won't be able to boot
>> 312 the new kernel image.
>> 313
>> 314 Reinstalling LILO is usually a matter of running /sbin/lilo.
>> 315 You may wish to edit /etc/lilo.conf to specify an entry for your
>> 316 old kernel image (say, /vmlinux.old) in case the new one does not
>> 317 work. See the LILO docs for more information.
>> 318
>> 319 After reinstalling LILO, you should be all set. Shutdown the system,
>> 320 reboot, and enjoy!
>> 321
>> 322 If you ever need to change the default root device, video mode,
>> 323 ramdisk size, etc. in the kernel image, use the 'rdev' program (or
>> 324 alternatively the LILO boot options when appropriate). No need to
>> 325 recompile the kernel to change these parameters.
>> 326
>> 327 - Reboot with the new kernel and enjoy.
>> 328
>> 329 IF SOMETHING GOES WRONG:
>> 330
>> 331 - If you have problems that seem to be due to kernel bugs, please check
>> 332 the file MAINTAINERS to see if there is a particular person associated
>> 333 with the part of the kernel that you are having trouble with. If there
>> 334 isn't anyone listed there, then the second best thing is to mail
>> 335 them to me (torvalds@linux-foundation.org), and possibly to any other
>> 336 relevant mailing-list or to the newsgroup.
>> 337
>> 338 - In all bug-reports, *please* tell what kernel you are talking about,
>> 339 how to duplicate the problem, and what your setup is (use your common
>> 340 sense). If the problem is new, tell me so, and if the problem is
>> 341 old, please try to tell me when you first noticed it.
>> 342
>> 343 - If the bug results in a message like
>> 344
>> 345 unable to handle kernel paging request at address C0000010
>> 346 Oops: 0002
>> 347 EIP: 0010:XXXXXXXX
>> 348 eax: xxxxxxxx ebx: xxxxxxxx ecx: xxxxxxxx edx: xxxxxxxx
>> 349 esi: xxxxxxxx edi: xxxxxxxx ebp: xxxxxxxx
>> 350 ds: xxxx es: xxxx fs: xxxx gs: xxxx
>> 351 Pid: xx, process nr: xx
>> 352 xx xx xx xx xx xx xx xx xx xx
>> 353
>> 354 or similar kernel debugging information on your screen or in your
>> 355 system log, please duplicate it *exactly*. The dump may look
>> 356 incomprehensible to you, but it does contain information that may
>> 357 help debugging the problem. The text above the dump is also
>> 358 important: it tells something about why the kernel dumped code (in
>> 359 the above example, it's due to a bad kernel pointer). More information
>> 360 on making sense of the dump is in Documentation/oops-tracing.txt
>> 361
>> 362 - If you compiled the kernel with CONFIG_KALLSYMS you can send the dump
>> 363 as is, otherwise you will have to use the "ksymoops" program to make
>> 364 sense of the dump (but compiling with CONFIG_KALLSYMS is usually preferred).
>> 365 This utility can be downloaded from
>> 366 ftp://ftp.<country>.kernel.org/pub/linux/utils/kernel/ksymoops/ .
>> 367 Alternatively, you can do the dump lookup by hand:
>> 368
>> 369 - In debugging dumps like the above, it helps enormously if you can
>> 370 look up what the EIP value means. The hex value as such doesn't help
>> 371 me or anybody else very much: it will depend on your particular
>> 372 kernel setup. What you should do is take the hex value from the EIP
>> 373 line (ignore the "0010:"), and look it up in the kernel namelist to
>> 374 see which kernel function contains the offending address.
>> 375
>> 376 To find out the kernel function name, you'll need to find the system
>> 377 binary associated with the kernel that exhibited the symptom. This is
>> 378 the file 'linux/vmlinux'. To extract the namelist and match it against
>> 379 the EIP from the kernel crash, do:
>> 380
>> 381 nm vmlinux | sort | less
>> 382
>> 383 This will give you a list of kernel addresses sorted in ascending
>> 384 order, from which it is simple to find the function that contains the
>> 385 offending address. Note that the address given by the kernel
>> 386 debugging messages will not necessarily match exactly with the
>> 387 function addresses (in fact, that is very unlikely), so you can't
>> 388 just 'grep' the list: the list will, however, give you the starting
>> 389 point of each kernel function, so by looking for the function that
>> 390 has a starting address lower than the one you are searching for but
>> 391 is followed by a function with a higher address you will find the one
>> 392 you want. In fact, it may be a good idea to include a bit of
>> 393 "context" in your problem report, giving a few lines around the
>> 394 interesting one.
>> 395
>> 396 If you for some reason cannot do the above (you have a pre-compiled
>> 397 kernel image or similar), telling me as much about your setup as
>> 398 possible will help. Please read the REPORTING-BUGS 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/i386/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.
15 412
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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