linux/README
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   1        Linux kernel release 4.x <http://kernel.org/>
   2
   3These are the release notes for Linux version 4.  Read them carefully,
   4as they tell you what this is all about, explain how to install the
   5kernel, and what to do if something goes wrong.
   6
   7WHAT IS LINUX?
   8
   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
  13  It has all the features you would expect in a modern fully-fledged Unix,
  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
  21ON 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
  37DOCUMENTATION:
  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
  59INSTALLING the kernel source:
  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   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
 113SOFTWARE 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
 124BUILD 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" allows 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
 145CONFIGURING 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"     Qt based configuration tool.
 163
 164     "make gconfig"     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    - A kernel with math-emulation compiled in will still use the
 233      coprocessor if one is present: the math emulation will just
 234      never get used in that case.  The kernel will be slightly larger,
 235      but will work on different machines regardless of whether they
 236      have a math coprocessor or not.
 237
 238    - The "kernel hacking" configuration details usually result in a
 239      bigger or slower kernel (or both), and can even make the kernel
 240      less stable by configuring some routines to actively try to
 241      break bad code to find kernel problems (kmalloc()).  Thus you
 242      should probably answer 'n' to the questions for "development",
 243      "experimental", or "debugging" features.
 244
 245COMPILING the kernel:
 246
 247 - Make sure you have at least gcc 3.2 available.
 248   For more information, refer to Documentation/Changes.
 249
 250   Please note that you can still run a.out user programs with this kernel.
 251
 252 - Do a "make" to create a compressed kernel image. It is also
 253   possible to do "make install" if you have lilo installed to suit the
 254   kernel makefiles, but you may want to check your particular lilo setup first.
 255
 256   To do the actual install, you have to be root, but none of the normal
 257   build should require that. Don't take the name of root in vain.
 258
 259 - If you configured any of the parts of the kernel as `modules', you
 260   will also have to do "make modules_install".
 261
 262 - Verbose kernel compile/build output:
 263
 264   Normally, the kernel build system runs in a fairly quiet mode (but not
 265   totally silent).  However, sometimes you or other kernel developers need
 266   to see compile, link, or other commands exactly as they are executed.
 267   For this, use "verbose" build mode.  This is done by passing
 268   "V=1" to the "make" command, e.g.
 269
 270     make V=1 all
 271
 272   To have the build system also tell the reason for the rebuild of each
 273   target, use "V=2".  The default is "V=0".
 274
 275 - Keep a backup kernel handy in case something goes wrong.  This is
 276   especially true for the development releases, since each new release
 277   contains new code which has not been debugged.  Make sure you keep a
 278   backup of the modules corresponding to that kernel, as well.  If you
 279   are installing a new kernel with the same version number as your
 280   working kernel, make a backup of your modules directory before you
 281   do a "make modules_install".
 282
 283   Alternatively, before compiling, use the kernel config option
 284   "LOCALVERSION" to append a unique suffix to the regular kernel version.
 285   LOCALVERSION can be set in the "General Setup" menu.
 286
 287 - In order to boot your new kernel, you'll need to copy the kernel
 288   image (e.g. .../linux/arch/x86/boot/bzImage after compilation)
 289   to the place where your regular bootable kernel is found.
 290
 291 - Booting a kernel directly from a floppy without the assistance of a
 292   bootloader such as LILO, is no longer supported.
 293
 294   If you boot Linux from the hard drive, chances are you use LILO, which
 295   uses the kernel image as specified in the file /etc/lilo.conf.  The
 296   kernel image file is usually /vmlinuz, /boot/vmlinuz, /bzImage or
 297   /boot/bzImage.  To use the new kernel, save a copy of the old image
 298   and copy the new image over the old one.  Then, you MUST RERUN LILO
 299   to update the loading map! If you don't, you won't be able to boot
 300   the new kernel image.
 301
 302   Reinstalling LILO is usually a matter of running /sbin/lilo.
 303   You may wish to edit /etc/lilo.conf to specify an entry for your
 304   old kernel image (say, /vmlinux.old) in case the new one does not
 305   work.  See the LILO docs for more information.
 306
 307   After reinstalling LILO, you should be all set.  Shutdown the system,
 308   reboot, and enjoy!
 309
 310   If you ever need to change the default root device, video mode,
 311   ramdisk size, etc.  in the kernel image, use the 'rdev' program (or
 312   alternatively the LILO boot options when appropriate).  No need to
 313   recompile the kernel to change these parameters.
 314
 315 - Reboot with the new kernel and enjoy.
 316
 317IF SOMETHING GOES WRONG:
 318
 319 - If you have problems that seem to be due to kernel bugs, please check
 320   the file MAINTAINERS to see if there is a particular person associated
 321   with the part of the kernel that you are having trouble with. If there
 322   isn't anyone listed there, then the second best thing is to mail
 323   them to me (torvalds@linux-foundation.org), and possibly to any other
 324   relevant mailing-list or to the newsgroup.
 325
 326 - In all bug-reports, *please* tell what kernel you are talking about,
 327   how to duplicate the problem, and what your setup is (use your common
 328   sense).  If the problem is new, tell me so, and if the problem is
 329   old, please try to tell me when you first noticed it.
 330
 331 - If the bug results in a message like
 332
 333     unable to handle kernel paging request at address C0000010
 334     Oops: 0002
 335     EIP:   0010:XXXXXXXX
 336     eax: xxxxxxxx   ebx: xxxxxxxx   ecx: xxxxxxxx   edx: xxxxxxxx
 337     esi: xxxxxxxx   edi: xxxxxxxx   ebp: xxxxxxxx
 338     ds: xxxx  es: xxxx  fs: xxxx  gs: xxxx
 339     Pid: xx, process nr: xx
 340     xx xx xx xx xx xx xx xx xx xx
 341
 342   or similar kernel debugging information on your screen or in your
 343   system log, please duplicate it *exactly*.  The dump may look
 344   incomprehensible to you, but it does contain information that may
 345   help debugging the problem.  The text above the dump is also
 346   important: it tells something about why the kernel dumped code (in
 347   the above example, it's due to a bad kernel pointer). More information
 348   on making sense of the dump is in Documentation/oops-tracing.txt
 349
 350 - If you compiled the kernel with CONFIG_KALLSYMS you can send the dump
 351   as is, otherwise you will have to use the "ksymoops" program to make
 352   sense of the dump (but compiling with CONFIG_KALLSYMS is usually preferred).
 353   This utility can be downloaded from
 354   ftp://ftp.<country>.kernel.org/pub/linux/utils/kernel/ksymoops/ .
 355   Alternatively, you can do the dump lookup by hand:
 356
 357 - In debugging dumps like the above, it helps enormously if you can
 358   look up what the EIP value means.  The hex value as such doesn't help
 359   me or anybody else very much: it will depend on your particular
 360   kernel setup.  What you should do is take the hex value from the EIP
 361   line (ignore the "0010:"), and look it up in the kernel namelist to
 362   see which kernel function contains the offending address.
 363
 364   To find out the kernel function name, you'll need to find the system
 365   binary associated with the kernel that exhibited the symptom.  This is
 366   the file 'linux/vmlinux'.  To extract the namelist and match it against
 367   the EIP from the kernel crash, do:
 368
 369     nm vmlinux | sort | less
 370
 371   This will give you a list of kernel addresses sorted in ascending
 372   order, from which it is simple to find the function that contains the
 373   offending address.  Note that the address given by the kernel
 374   debugging messages will not necessarily match exactly with the
 375   function addresses (in fact, that is very unlikely), so you can't
 376   just 'grep' the list: the list will, however, give you the starting
 377   point of each kernel function, so by looking for the function that
 378   has a starting address lower than the one you are searching for but
 379   is followed by a function with a higher address you will find the one
 380   you want.  In fact, it may be a good idea to include a bit of
 381   "context" in your problem report, giving a few lines around the
 382   interesting one.
 383
 384   If you for some reason cannot do the above (you have a pre-compiled
 385   kernel image or similar), telling me as much about your setup as
 386   possible will help.  Please read the REPORTING-BUGS document for details.
 387
 388 - Alternatively, you can use gdb on a running kernel. (read-only; i.e. you
 389   cannot change values or set break points.) To do this, first compile the
 390   kernel with -g; edit arch/x86/Makefile appropriately, then do a "make
 391   clean". You'll also need to enable CONFIG_PROC_FS (via "make config").
 392
 393   After you've rebooted with the new kernel, do "gdb vmlinux /proc/kcore".
 394   You can now use all the usual gdb commands. The command to look up the
 395   point where your system crashed is "l *0xXXXXXXXX". (Replace the XXXes
 396   with the EIP value.)
 397
 398   gdb'ing a non-running kernel currently fails because gdb (wrongly)
 399   disregards the starting offset for which the kernel is compiled.
 400
 401
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