linux/README
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   1        Linux kernel release 3.x <http://kernel.org/>
   2
   3These are the release notes for Linux version 3.  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 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 (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
 121SOFTWARE 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
 132BUILD 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
 153CONFIGURING 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
 257COMPILING 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
 329IF 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.
 412
 413
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