Linux kernel release 4.x <http://kernel.org/>

  These are the release notes for Linux version 4.  Read them carefully,

  as they tell you what this is all about, explain how to install the

  kernel, and what to do if something goes wrong.

  
  WHAT IS LINUX?

    Linux is a clone of the operating system Unix, written from scratch by
    Linus Torvalds with assistance from a loosely-knit team of hackers across
    the Net. It aims towards POSIX and Single UNIX Specification compliance.

    It has all the features you would expect in a modern fully-fledged Unix,
    including true multitasking, virtual memory, shared libraries, demand
    loading, shared copy-on-write executables, proper memory management,
    and multistack networking including IPv4 and IPv6.

  
    It is distributed under the GNU General Public License - see the

    accompanying COPYING file for more details.

  
  ON WHAT HARDWARE DOES IT RUN?

    Although originally developed first for 32-bit x86-based PCs (386 or higher),
    today Linux also runs on (at least) the Compaq Alpha AXP, Sun SPARC and

    UltraSPARC, Motorola 68000, PowerPC, PowerPC64, ARM, Hitachi SuperH, Cell,

    IBM S/390, MIPS, HP PA-RISC, Intel IA-64, DEC VAX, AMD x86-64, AXIS CRIS,

    Xtensa, Tilera TILE, AVR32, ARC and Renesas M32R architectures.

  
    Linux is easily portable to most general-purpose 32- or 64-bit architectures
    as long as they have a paged memory management unit (PMMU) and a port of the
    GNU C compiler (gcc) (part of The GNU Compiler Collection, GCC). Linux has
    also been ported to a number of architectures without a PMMU, although
    functionality is then obviously somewhat limited.

    Linux has also been ported to itself. You can now run the kernel as a
    userspace application - this is called UserMode Linux (UML).

  
  DOCUMENTATION:
  
   - There is a lot of documentation available both in electronic form on
     the Internet and in books, both Linux-specific and pertaining to
     general UNIX questions.  I'd recommend looking into the documentation
     subdirectories on any Linux FTP site for the LDP (Linux Documentation
     Project) books.  This README is not meant to be documentation on the
     system: there are much better sources available.
  
   - There are various README files in the Documentation/ subdirectory:

     these typically contain kernel-specific installation notes for some

     drivers for example. See Documentation/00-INDEX for a list of what
     is contained in each file.  Please read the Changes file, as it
     contains information about the problems, which may result by upgrading
     your kernel.
  
   - The Documentation/DocBook/ subdirectory contains several guides for
     kernel developers and users.  These guides can be rendered in a

     number of formats:  PostScript (.ps), PDF, HTML, & man-pages, among others.
     After installation, "make psdocs", "make pdfdocs", "make htmldocs",
     or "make mandocs" will render the documentation in the requested format.

  INSTALLING the kernel source:

  
   - If you install the full sources, put the kernel tarball in a

     directory where you have permissions (e.g. your home directory) and

     unpack it:

       xz -cd linux-4.X.tar.xz | tar xvf -

     Replace "X" with the version number of the latest kernel.

  
     Do NOT use the /usr/src/linux area! This area has a (usually
     incomplete) set of kernel headers that are used by the library header
     files.  They should match the library, and not get messed up by
     whatever the kernel-du-jour happens to be.

   - You can also upgrade between 4.x releases by patching.  Patches are

     distributed in the xz format.  To install by patching, get all the
     newer patch files, enter the top level directory of the kernel source
     (linux-4.X) and execute:

       xz -cd ../patch-4.x.xz | patch -p1

     Replace "x" for all versions bigger than the version "X" of your current
     source tree, _in_order_, and you should be ok.  You may want to remove
     the backup files (some-file-name~ or some-file-name.orig), and make sure
     that there are no failed patches (some-file-name# or some-file-name.rej).

     If there are, either you or I have made a mistake.

     Unlike patches for the 4.x kernels, patches for the 4.x.y kernels

     (also known as the -stable kernels) are not incremental but instead apply

     directly to the base 4.x kernel.  For example, if your base kernel is 4.0
     and you want to apply the 4.0.3 patch, you must not first apply the 4.0.1
     and 4.0.2 patches. Similarly, if you are running kernel version 4.0.2 and
     want to jump to 4.0.3, you must first reverse the 4.0.2 patch (that is,
     patch -R) _before_ applying the 4.0.3 patch. You can read more on this in

     Documentation/applying-patches.txt

     Alternatively, the script patch-kernel can be used to automate this
     process.  It determines the current kernel version and applies any
     patches found.

       linux/scripts/patch-kernel linux

  
     The first argument in the command above is the location of the
     kernel source.  Patches are applied from the current directory, but
     an alternative directory can be specified as the second argument.
  
   - Make sure you have no stale .o files and dependencies lying around:

       cd linux
       make mrproper

  
     You should now have the sources correctly installed.
  
  SOFTWARE REQUIREMENTS

     Compiling and running the 4.x kernels requires up-to-date

     versions of various software packages.  Consult
     Documentation/Changes for the minimum version numbers required
     and how to get updates for these packages.  Beware that using
     excessively old versions of these packages can cause indirect
     errors that are very difficult to track down, so don't assume that
     you can just update packages when obvious problems arise during
     build or operation.
  
  BUILD directory for the kernel:

     When compiling the kernel, all output files will per default be

     stored together with the kernel source code.

     Using the option "make O=output/dir" allows you to specify an alternate

     place for the output files (including .config).
     Example:

       kernel source code: /usr/src/linux-4.X

       build directory:    /home/name/build/kernel

     To configure and build the kernel, use:

       cd /usr/src/linux-4.X

       make O=/home/name/build/kernel menuconfig
       make O=/home/name/build/kernel
       sudo make O=/home/name/build/kernel modules_install install

     Please note: If the 'O=output/dir' option is used, then it must be

     used for all invocations of make.
  
  CONFIGURING the kernel:
  
     Do not skip this step even if you are only upgrading one minor
     version.  New configuration options are added in each release, and
     odd problems will turn up if the configuration files are not set up
     as expected.  If you want to carry your existing configuration to a
     new version with minimal work, use "make oldconfig", which will
     only ask you for the answers to new questions.

   - Alternative configuration commands are:

       "make config"      Plain text interface.

       "make menuconfig"  Text based color menus, radiolists & dialogs.

       "make nconfig"     Enhanced text based color menus.

       "make xconfig"     Qt based configuration tool.

       "make gconfig"     GTK+ based configuration tool.

       "make oldconfig"   Default all questions based on the contents of
                          your existing ./.config file and asking about
                          new config symbols.

       "make silentoldconfig"
                          Like above, but avoids cluttering the screen
                          with questions already answered.
                          Additionally updates the dependencies.

       "make olddefconfig"
                          Like above, but sets new symbols to their default
                          values without prompting.

       "make defconfig"   Create a ./.config file by using the default
                          symbol values from either arch/$ARCH/defconfig
                          or arch/$ARCH/configs/${PLATFORM}_defconfig,
                          depending on the architecture.

       "make ${PLATFORM}_defconfig"
                          Create a ./.config file by using the default
                          symbol values from
                          arch/$ARCH/configs/${PLATFORM}_defconfig.
                          Use "make help" to get a list of all available
                          platforms of your architecture.

       "make allyesconfig"
                          Create a ./.config file by setting symbol
                          values to 'y' as much as possible.

       "make allmodconfig"
                          Create a ./.config file by setting symbol
                          values to 'm' as much as possible.

       "make allnoconfig" Create a ./.config file by setting symbol
                          values to 'n' as much as possible.

       "make randconfig"  Create a ./.config file by setting symbol
                          values to random values.

       "make localmodconfig" Create a config based on current config and
                             loaded modules (lsmod). Disables any module
                             option that is not needed for the loaded modules.
  
                             To create a localmodconfig for another machine,
                             store the lsmod of that machine into a file
                             and pass it in as a LSMOD parameter.
  
                     target$ lsmod > /tmp/mylsmod
                     target$ scp /tmp/mylsmod host:/tmp
  
                     host$ make LSMOD=/tmp/mylsmod localmodconfig
  
                             The above also works when cross compiling.
  
       "make localyesconfig" Similar to localmodconfig, except it will convert
                             all module options to built in (=y) options.

     You can find more information on using the Linux kernel config tools

     in Documentation/kbuild/kconfig.txt.

   - NOTES on "make config":

      - Having unnecessary drivers will make the kernel bigger, and can
        under some circumstances lead to problems: probing for a
        nonexistent controller card may confuse your other controllers

      - A kernel with math-emulation compiled in will still use the
        coprocessor if one is present: the math emulation will just
        never get used in that case.  The kernel will be slightly larger,
        but will work on different machines regardless of whether they
        have a math coprocessor or not.

      - The "kernel hacking" configuration details usually result in a
        bigger or slower kernel (or both), and can even make the kernel
        less stable by configuring some routines to actively try to
        break bad code to find kernel problems (kmalloc()).  Thus you
        should probably answer 'n' to the questions for "development",
        "experimental", or "debugging" features.

  COMPILING the kernel:

   - Make sure you have at least gcc 3.2 available.
     For more information, refer to Documentation/Changes.

  
     Please note that you can still run a.out user programs with this kernel.
  
   - Do a "make" to create a compressed kernel image. It is also
     possible to do "make install" if you have lilo installed to suit the
     kernel makefiles, but you may want to check your particular lilo setup first.

     To do the actual install, you have to be root, but none of the normal

     build should require that. Don't take the name of root in vain.
  
   - If you configured any of the parts of the kernel as `modules', you
     will also have to do "make modules_install".

   - Verbose kernel compile/build output:

     Normally, the kernel build system runs in a fairly quiet mode (but not

     totally silent).  However, sometimes you or other kernel developers need
     to see compile, link, or other commands exactly as they are executed.

     For this, use "verbose" build mode.  This is done by passing
     "V=1" to the "make" command, e.g.

       make V=1 all

  
     To have the build system also tell the reason for the rebuild of each
     target, use "V=2".  The default is "V=0".

   - Keep a backup kernel handy in case something goes wrong.  This is

     especially true for the development releases, since each new release
     contains new code which has not been debugged.  Make sure you keep a
     backup of the modules corresponding to that kernel, as well.  If you
     are installing a new kernel with the same version number as your
     working kernel, make a backup of your modules directory before you
     do a "make modules_install".

     Alternatively, before compiling, use the kernel config option
     "LOCALVERSION" to append a unique suffix to the regular kernel version.
     LOCALVERSION can be set in the "General Setup" menu.

  
   - In order to boot your new kernel, you'll need to copy the kernel

     image (e.g. .../linux/arch/x86/boot/bzImage after compilation)

     to the place where your regular bootable kernel is found.

  
   - Booting a kernel directly from a floppy without the assistance of a
     bootloader such as LILO, is no longer supported.

     If you boot Linux from the hard drive, chances are you use LILO, which

     uses the kernel image as specified in the file /etc/lilo.conf.  The
     kernel image file is usually /vmlinuz, /boot/vmlinuz, /bzImage or
     /boot/bzImage.  To use the new kernel, save a copy of the old image
     and copy the new image over the old one.  Then, you MUST RERUN LILO

     to update the loading map! If you don't, you won't be able to boot

     the new kernel image.

     Reinstalling LILO is usually a matter of running /sbin/lilo.

     You may wish to edit /etc/lilo.conf to specify an entry for your
     old kernel image (say, /vmlinux.old) in case the new one does not

     work.  See the LILO docs for more information.

  
     After reinstalling LILO, you should be all set.  Shutdown the system,
     reboot, and enjoy!
  
     If you ever need to change the default root device, video mode,
     ramdisk size, etc.  in the kernel image, use the 'rdev' program (or
     alternatively the LILO boot options when appropriate).  No need to

     recompile the kernel to change these parameters.

   - Reboot with the new kernel and enjoy.

  
  IF SOMETHING GOES WRONG:
  
   - If you have problems that seem to be due to kernel bugs, please check
     the file MAINTAINERS to see if there is a particular person associated
     with the part of the kernel that you are having trouble with. If there
     isn't anyone listed there, then the second best thing is to mail

     them to me (torvalds@linux-foundation.org), and possibly to any other
     relevant mailing-list or to the newsgroup.

  
   - In all bug-reports, *please* tell what kernel you are talking about,
     how to duplicate the problem, and what your setup is (use your common
     sense).  If the problem is new, tell me so, and if the problem is
     old, please try to tell me when you first noticed it.
  
   - If the bug results in a message like

       unable to handle kernel paging request at address C0000010
       Oops: 0002
       EIP:   0010:XXXXXXXX
       eax: xxxxxxxx   ebx: xxxxxxxx   ecx: xxxxxxxx   edx: xxxxxxxx
       esi: xxxxxxxx   edi: xxxxxxxx   ebp: xxxxxxxx
       ds: xxxx  es: xxxx  fs: xxxx  gs: xxxx
       Pid: xx, process nr: xx
       xx xx xx xx xx xx xx xx xx xx

  
     or similar kernel debugging information on your screen or in your
     system log, please duplicate it *exactly*.  The dump may look
     incomprehensible to you, but it does contain information that may
     help debugging the problem.  The text above the dump is also
     important: it tells something about why the kernel dumped code (in

     the above example, it's due to a bad kernel pointer). More information

     on making sense of the dump is in Documentation/oops-tracing.txt
  
   - If you compiled the kernel with CONFIG_KALLSYMS you can send the dump
     as is, otherwise you will have to use the "ksymoops" program to make

     sense of the dump (but compiling with CONFIG_KALLSYMS is usually preferred).
     This utility can be downloaded from
     ftp://ftp.<country>.kernel.org/pub/linux/utils/kernel/ksymoops/ .

     Alternatively, you can do the dump lookup by hand:

  
   - In debugging dumps like the above, it helps enormously if you can
     look up what the EIP value means.  The hex value as such doesn't help
     me or anybody else very much: it will depend on your particular
     kernel setup.  What you should do is take the hex value from the EIP
     line (ignore the "0010:"), and look it up in the kernel namelist to
     see which kernel function contains the offending address.
  
     To find out the kernel function name, you'll need to find the system
     binary associated with the kernel that exhibited the symptom.  This is
     the file 'linux/vmlinux'.  To extract the namelist and match it against
     the EIP from the kernel crash, do:

       nm vmlinux | sort | less

  
     This will give you a list of kernel addresses sorted in ascending
     order, from which it is simple to find the function that contains the
     offending address.  Note that the address given by the kernel
     debugging messages will not necessarily match exactly with the
     function addresses (in fact, that is very unlikely), so you can't
     just 'grep' the list: the list will, however, give you the starting
     point of each kernel function, so by looking for the function that
     has a starting address lower than the one you are searching for but
     is followed by a function with a higher address you will find the one
     you want.  In fact, it may be a good idea to include a bit of
     "context" in your problem report, giving a few lines around the

     interesting one.

  
     If you for some reason cannot do the above (you have a pre-compiled
     kernel image or similar), telling me as much about your setup as

     possible will help.  Please read the REPORTING-BUGS document for details.

   - Alternatively, you can use gdb on a running kernel. (read-only; i.e. you

     cannot change values or set break points.) To do this, first compile the

     kernel with -g; edit arch/x86/Makefile appropriately, then do a "make

     clean". You'll also need to enable CONFIG_PROC_FS (via "make config").
  
     After you've rebooted with the new kernel, do "gdb vmlinux /proc/kcore".
     You can now use all the usual gdb commands. The command to look up the
     point where your system crashed is "l *0xXXXXXXXX". (Replace the XXXes
     with the EIP value.)
  
     gdb'ing a non-running kernel currently fails because gdb (wrongly)
     disregards the starting offset for which the kernel is compiled.