README

   1         Linux kernel release 4.x <http://kernel.org/>
   2
   3 These are the release notes for Linux version 4.  Read them carefully,
   4 as they tell you what this is all about, explain how to install the
   5 kernel, and what to do if something goes wrong.
   6
   7 WHAT 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
  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.
 404