linux/Documentation/admin-guide
Lukas Bulwahn d546978e0c docs: admin-guide: remove obsolete advice related to SLAB allocator
Commit 1db9d06aaa55 ("mm/slab: remove CONFIG_SLAB from all Kconfig and
Makefile") removes the config SLAB and makes the SLUB allocator the only
default allocator in the kernel. Hence, the advice on reducing OS jitter
due to kworker kernel threads to build with CONFIG_SLUB instead of
CONFIG_SLAB is obsolete.

Remove the obsolete advice to build with SLUB instead of SLAB.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20231130095515.21586-1-lukas.bulwahn@gmail.com
2024-01-23 14:52:37 -07:00
..
acpi Documentation: admin-guide: PM: Fix two typos 2024-01-10 15:10:44 +01:00
aoe
auxdisplay
blockdev zram: split memory-tracking and ac-time tracking 2023-12-10 16:51:40 -08:00
cgroup-v1 memcg: expose swapcache stat for memcg v1 2023-10-06 14:44:10 -07:00
cifs cifs: update known bugs mentioned in kernel docs for cifs 2024-01-19 10:30:22 -06:00
device-mapper Documentation: dm-integrity: Document an example of how the tunables relate. 2023-06-22 18:39:51 -04:00
gpio gpiolib: remove legacy gpio_export() 2023-03-06 12:33:01 +02:00
hw-vuln The number of commits for documentation is not huge this time around, but 2023-11-01 17:11:41 -10:00
kdump mm, treewide: rename MAX_ORDER to MAX_PAGE_ORDER 2024-01-08 15:27:15 -08:00
laptops platform/x86: thinkpad_acpi: sysfs interface to auxmac 2023-09-28 13:12:36 +03:00
LSM
media media updates for v6.8-rc1 2024-01-12 14:29:48 -08:00
mm zswap: memcontrol: implement zswap writeback disabling 2023-12-29 20:22:11 -08:00
namespaces
nfs
perf docs: perf: Add description for Synopsys DesignWare PCIe PMU driver 2023-12-13 13:35:41 +00:00
pm Documentation: admin-guide: PM: Fix two typos 2024-01-10 15:10:44 +01:00
sysctl net: increase optmem_max default value 2023-12-15 11:01:26 +00:00
thermal It has been a moderately calm cycle for documentation; the significant 2023-02-22 12:00:20 -08:00
abi-obsolete.rst docs: kernel_abi.py: fix command injection 2024-01-03 13:44:11 -07:00
abi-removed.rst docs: kernel_abi.py: fix command injection 2024-01-03 13:44:11 -07:00
abi-stable.rst docs: kernel_abi.py: fix command injection 2024-01-03 13:44:11 -07:00
abi-testing.rst docs: kernel_abi.py: fix command injection 2024-01-03 13:44:11 -07:00
abi.rst
bcache.rst bcache: Remove dead references to cache_readaheads 2023-06-15 07:30:11 -06:00
binderfs.rst
binfmt-misc.rst
bootconfig.rst Allow forcing unconditional bootconfig processing 2023-02-22 08:27:48 +09:00
braille-console.rst
btmrvl.rst
bug-bisect.rst
bug-hunting.rst
cgroup-v2.rst Many singleton patches against the MM code. The patch series which 2024-01-09 11:18:47 -08:00
clearing-warn-once.rst
cpu-load.rst
cputopology.rst
dell_rbu.rst
devices.rst
devices.txt Documentation: devices.txt: Update ttyUL major number allocation details 2023-11-25 07:23:16 +00:00
dynamic-debug-howto.rst Documentation: Remove redundant file names from examples 2023-12-15 09:15:05 -07:00
edid.rst
efi-stub.rst Documentation efi-stub.rst: fix arm64 EFI source location 2023-09-22 05:29:19 -06:00
ext4.rst ext4: Remove the logic to trim inode PAs 2023-04-06 01:13:13 -04:00
features.rst docs: kernel_feat.py: fix potential command injection 2024-01-11 09:21:01 -07:00
filesystem-monitoring.rst
highuid.rst
hw_random.rst docs: admin-guide: hw_random: update rng-tools website 2024-01-11 09:35:18 -07:00
index.rst platform/x86/amd/pmf: Add support to update system state 2023-12-18 12:47:46 +01:00
init.rst
initrd.rst
iostats.rst
java.rst
jfs.rst
kernel-parameters.rst doc: admin-guide/kernel-parameters: remove useless comment 2024-01-23 14:46:52 -07:00
kernel-parameters.txt LoongArch changes for v6.8 2024-01-19 13:30:49 -08:00
kernel-per-CPU-kthreads.rst docs: admin-guide: remove obsolete advice related to SLAB allocator 2024-01-23 14:52:37 -07:00
lcd-panel-cgram.rst
ldm.rst
lockup-watchdogs.rst
md.rst Documentation: admin-guide: correct spelling 2023-02-02 11:04:42 -07:00
module-signing.rst Documentation/module-signing.txt: bring up to date 2023-10-27 18:04:30 +08:00
mono.rst
numastat.rst
parport.rst
perf-security.rst
pmf.rst platform/x86/amd/pmf: Add support to update system state 2023-12-18 12:47:46 +01:00
pnp.rst
pstore-blk.rst docs: pstore-blk.rst: fix typo, s/console/ftrace 2023-09-23 20:45:26 -07:00
quickly-build-trimmed-linux.rst docs: quickly-build-trimmed-linux: various small fixes and improvements 2023-05-16 12:50:05 -06:00
ramoops.rst
rapidio.rst
ras.rst docs: move x86 documentation into Documentation/arch/ 2023-03-30 12:58:51 -06:00
README.rst There's not a huge amount of activity in the docs tree this time around, 2022-10-03 10:23:32 -07:00
reporting-issues.rst Documentation/security-bugs: move from admin-guide/ to process/ 2023-03-12 15:56:43 +01:00
reporting-regressions.rst
rtc.rst
serial-console.rst Documentation: serial-console: Fix literal block marker 2023-08-28 12:42:03 -06:00
spkguide.txt speakup: Document USB support 2023-10-26 11:35:21 -06:00
svga.rst
syscall-user-dispatch.rst ptrace: Provide set/get interface for syscall user dispatch 2023-04-16 14:23:07 +02:00
sysfs-rules.rst
sysrq.rst /proc/sysrq-trigger: accept multiple keys at once 2023-11-25 07:23:16 +00:00
tainted-kernels.rst
thunderbolt.rst
ufs.rst
unicode.rst docs: admin: unicode: update information on state of lanana.org document 2023-03-14 12:27:39 -06:00
vga-softcursor.rst
video-output.rst
workload-tracing.rst docs: add workload-tracing document to admin-guide 2023-02-02 10:43:13 -07:00
xfs.rst Documentation: admin-guide: correct "it's" to possessive "its" 2023-07-14 13:17:55 -06:00

.. _readme:

Linux kernel release 6.x <http://kernel.org/>
=============================================

These are the release notes for Linux version 6.  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 v2 - 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 Xtensa, and
  ARC 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. Please read the
   :ref:`Documentation/process/changes.rst <changes>` file, as it
   contains information about the problems, which may result by upgrading
   your kernel.

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-6.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 6.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-6.x) and execute::

     xz -cd ../patch-6.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 6.x kernels, patches for the 6.x.y kernels
   (also known as the -stable kernels) are not incremental but instead apply
   directly to the base 6.x kernel.  For example, if your base kernel is 6.0
   and you want to apply the 6.0.3 patch, you must not first apply the 6.0.1
   and 6.0.2 patches. Similarly, if you are running kernel version 6.0.2 and
   want to jump to 6.0.3, you must first reverse the 6.0.2 patch (that is,
   patch -R) **before** applying the 6.0.3 patch. You can read more on this in
   :ref:`Documentation/process/applying-patches.rst <applying_patches>`.

   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 6.x kernels requires up-to-date
   versions of various software packages.  Consult
   :ref:`Documentation/process/changes.rst <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-6.x
     build directory:    /home/name/build/kernel

   To configure and build the kernel, use::

     cd /usr/src/linux-6.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 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.

                           Also, you can preserve modules in certain folders
                           or kconfig files by specifying their paths in
                           parameter LMC_KEEP.

                   target$ lsmod > /tmp/mylsmod
                   target$ scp /tmp/mylsmod host:/tmp

                   host$ make LSMOD=/tmp/mylsmod \
                           LMC_KEEP="drivers/usb:drivers/gpu:fs" \
                           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
                           also preserve modules by LMC_KEEP.

     "make kvm_guest.config"   Enable additional options for kvm guest kernel
                               support.

     "make xen.config"   Enable additional options for xen dom0 guest kernel
                         support.

     "make tinyconfig"  Configure the tiniest possible kernel.

   You can find more information on using the Linux kernel config tools
   in Documentation/kbuild/kconfig.rst.

 - 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 5.1 available.
   For more information, refer to :ref:`Documentation/process/changes.rst <changes>`.

 - 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,
   etc. in the kernel image, use your bootloader's boot options
   where 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 follow the
instructions at 'Documentation/admin-guide/reporting-issues.rst'.

Hints on understanding kernel bug reports are in
'Documentation/admin-guide/bug-hunting.rst'. More on debugging the kernel
with gdb is in 'Documentation/dev-tools/gdb-kernel-debugging.rst' and
'Documentation/dev-tools/kgdb.rst'.