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linux/Documentation/process/changes.rst
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Lorenzo Stoakes (ARM) 48ebe1cbbe kbuild: compress the kernel with pigz if available 
The gzip step of a kernel build is very lengthy, especially for larger
builds such as allmodconfig.

gzip itself cannot be run in parallel, however an alternative tool exists
that can, providing the same feature set as gzip itself - pigz - which
works as a drop-in replacement.

On a 128-core Threadripper, gzip -9 of a 36 MiB x86-64 vmlinux.bin takes
1.6s, and with pigz it takes 0.09s, so the performance increase is
significant.

Therefore introduce the KPGZIP build variable which specifies the
compressor to use for the kernel image and default it to pigz if available,
or KGZIP otherwise (which itself defaults to gzip).

Modules, packaging and the embedded kernel configuration (CONFIG_IKCONFIG)
continue to use KGZIP which defaults to a single-threaded gzip instance.

Module compression is run in parallel by make, so pigz offers no benefit
there, packaging sits outside the build and the embedded configuration is
too small to matter.

pigz is executed using scripts/jobserver-exec, which reserves the job slots
make has free - necessary, as otherwise pigz would just grab unbounded
CPUs.

The kernel image compression step is always performed at the end of the
build so should typically have all job slots available.

pigz always provides byte-for-byte identical output across runs regardless
of thread count, but pigz and gzip are not guaranteed to generate the same
binary output, so reproducible builds must use the same tools consistently.

Also update Documentation/kbuild/kbuild.rst to describe KPGZIP and
Documentation/process/changes.rst to list the optional pigz dependency.

While there, add entries for the other compressor programs.

Finally, update scripts/ver_linux to include the pigz version there.

Every x86 build ends with the compression of vmlinux.bin, 36MB for
defconfig and over 200MB for allmodconfig, no-op builds are unchanged.

Whole build, 128-thread Threadripper 9980X, best of N runs:

                                         before   after     delta
                                         -------------------------------
  x86 defconfig, touch mm/vma.c, gcc        7.7s     6.0s     -1.7s (-22%)
  x86 defconfig, touch mm/vma.c, clang      6.9s     5.4s     -1.5s (-21%)
  x86 defconfig, clean, gcc                28.2s    26.3s     -1.8s (-6%)
  x86 defconfig, clean, clang              28.7s    27.2s     -1.5s (-5%)
  x86 allmodconfig, touch mm/vma.c, gcc    23.7s    15.4s     -8.3s (-35%)
  x86 allmodconfig, touch mm/vma.c, clang  22.5s    15.6s     -7.0s (-31%)
  x86 allmodconfig, clean, gcc            294.1s   278.6s     -15.5s (-5%)
  x86 allmodconfig, clean, clang          283.9s   266.8s     -17.1s (-6%)

Suggested-by: Kees Cook <kees@kernel.org>
Link: https://zlib.net/pigz/
Assisted-by: LLM
Reviewed-by: Manuel Ebner <manuelebnerli@mailbox.org>
Reviewed-by: Kees Cook <kees@kernel.org>
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Link: https://patch.msgid.link/20260923-build-speedup-v4-22-73128809a4a4@kernel.org
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
2026-09-26 00:16:36 +01:00

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.. _changes:
Minimal requirements to compile the Kernel
++++++++++++++++++++++++++++++++++++++++++
Intro
=====
This document is designed to provide a list of the minimum levels of
software necessary to run the current kernel version.
This document is originally based on my "Changes" file for 2.0.x kernels
and therefore owes credit to the same people as that file (Jared Mauch,
Axel Boldt, Alessandro Sigala, and countless other users all over the
'net).
Current Minimal Requirements
****************************
Upgrade to at **least** these software revisions before thinking you've
encountered a bug! If you're unsure what version you're currently
running, the suggested command should tell you. For a list of the programs
on your system including their version execute ./scripts/ver_linux
Again, keep in mind that this list assumes you are already functionally
running a Linux kernel. Also, not all tools are necessary on all
systems; obviously, if you don't have any PC Card hardware, for example,
you probably do not need to concern yourself with pcmciautils.
====================== =============== ========================================
Program Minimal version Command to check the version
====================== =============== ========================================
bash 4.2 bash --version
bc 1.06.95 bc --version
bindgen (optional) 0.71.1 bindgen --version
binutils 2.30 ld -v
bison 2.0 bison --version
btrfs-progs 0.18 btrfs --version
Clang/LLVM (optional) 17.0.1 clang --version
e2fsprogs 1.41.4 e2fsck -V
flex 2.5.35 flex --version
gdb 7.2 gdb --version
GNU awk (optional) 5.1.0 gawk --version
GNU C 8.1 gcc --version
GNU make 4.0 make --version
GNU tar 1.28 tar --version
GRUB 0.93 grub --version || grub-install --version
gtags (optional) 6.6.5 gtags --version
iptables 1.4.2 iptables -V
jfsutils 1.1.3 fsck.jfs -V
kmod 13 kmod -V
mcelog 0.6 mcelog --version
mkimage (optional) 2017.01 mkimage --version
nfs-utils 1.0.5 showmount --version
openssl & libcrypto 1.0.0 openssl version
pahole 1.26 pahole --version
pcmciautils 004 pccardctl -V
pigz (optional) 2.4 pigz --version
PPP 2.4.0 pppd --version
procps 3.2.0 ps --version
Python 3.9.x python3 --version
quota-tools 3.09 quota -V
Rust (optional) 1.85.0 rustc --version
Sphinx\ [#f1]_ 3.4.3 sphinx-build --version
squashfs-tools 4.0 mksquashfs -version
udev 081 udevadm --version
util-linux 2.10o mount --version
xfsprogs 2.6.0 xfs_db -V
====================== =============== ========================================
.. [#f1] Sphinx is needed only to build the Kernel documentation
Kernel compilation
******************
GCC
---
The gcc version requirements may vary depending on the type of CPU in your
computer.
Clang/LLVM (optional)
---------------------
The latest formal release of clang and LLVM utils (according to
`releases.llvm.org <https://releases.llvm.org>`_) are supported for building
kernels. Older releases aren't guaranteed to work, and we may drop workarounds
from the kernel that were used to support older versions. Please see additional
docs on :ref:`Building Linux with Clang/LLVM <kbuild_llvm>`.
Rust (optional)
---------------
A recent version of the Rust compiler is required.
Please see Documentation/rust/quick-start.rst for instructions on how to
satisfy the build requirements of Rust support. In particular, the ``Makefile``
target ``rustavailable`` is useful to check why the Rust toolchain may not
be detected.
bindgen (optional)
------------------
``bindgen`` is used to generate the Rust bindings to the C side of the kernel.
It depends on ``libclang``.
Make
----
You will need GNU make 4.0 or later to build the kernel.
Bash
----
Some bash scripts are used for the kernel build.
Bash 4.2 or newer is needed.
Binutils
--------
Binutils 2.30 or newer is needed to build the kernel.
pkg-config
----------
The build system, as of 4.18, requires pkg-config to check for installed
kconfig tools and to determine flags settings for use in
'make {g,x}config'. Previously pkg-config was being used but not
verified or documented.
Flex
----
Since Linux 4.16, the build system generates lexical analyzers
during build. This requires flex 2.5.35 or later.
Bison
-----
Since Linux 4.16, the build system generates parsers
during build. This requires bison 2.0 or later.
pahole
------
Since Linux 5.2, if CONFIG_DEBUG_INFO_BTF is selected, the build system
generates BTF (BPF Type Format) from DWARF in vmlinux, a bit later from kernel
modules as well. This requires pahole v1.22 or later.
It is found in the 'dwarves' or 'pahole' distro packages or from
https://fedorapeople.org/~acme/dwarves/.
Perl
----
You will need perl 5 and the following modules: ``Getopt::Long``,
``Getopt::Std``, ``File::Basename``, and ``File::Find`` to build the kernel.
Python
------
Several config options require it: it is required for arm/arm64
default configs, CONFIG_LTO_CLANG, some DRM optional configs,
the kernel-doc tool, and docs build (Sphinx), among others.
BC
--
You will need bc to build kernels 3.10 and higher
OpenSSL
-------
Module signing and external certificate handling use the OpenSSL program and
crypto library to do key creation and signature generation.
You will need openssl to build kernels 3.7 and higher if module signing is
enabled. You will also need openssl development packages to build kernels 4.3
and higher.
Tar
---
GNU tar is needed if you want to enable access to the kernel headers via sysfs
(CONFIG_IKHEADERS).
gtags / GNU GLOBAL (optional)
-----------------------------
The kernel build requires GNU GLOBAL version 6.6.5 or later to generate
tag files through ``make gtags``. This is due to its use of the gtags
``-C (--directory)`` flag.
mkimage
-------
This tool is used when building a Flat Image Tree (FIT), commonly used on ARM
platforms. The tool is available via the ``u-boot-tools`` package or can be
built from the U-Boot source code. See the instructions at
https://docs.u-boot.org/en/latest/build/tools.html#building-tools-for-linux
GNU AWK
-------
GNU AWK is needed if you want kernel builds to generate address range data for
builtin modules (CONFIG_BUILTIN_MODULE_RANGES).
pigz (optional)
---------------
pigz is a parallel implementation of gzip. If it is installed the compressed
kernel image is produced with it rather than with gzip, see ``KPGZIP`` in
Documentation/kbuild/kbuild.rst.
System utilities
****************
Architectural changes
---------------------
DevFS has been obsoleted in favour of udev
(https://www.kernel.org/pub/linux/utils/kernel/hotplug/)
32-bit UID support is now in place. Have fun!
Linux documentation for functions is transitioning to inline
documentation via specially-formatted comments near their
definitions in the source. These comments can be combined with ReST
files in the Documentation/ directory to make enriched documentation, which can
then be converted to PostScript, HTML, LaTex, ePUB and PDF files.
In order to convert from ReST format to a format of your choice, you'll need
Sphinx.
Util-linux
----------
New versions of util-linux provide ``fdisk`` support for larger disks,
support new options to mount, recognize more supported partition
types, and similar goodies.
You'll probably want to upgrade.
Ksymoops
--------
If the unthinkable happens and your kernel oopses, you may need the
ksymoops tool to decode it, but in most cases you don't.
It is generally preferred to build the kernel with ``CONFIG_KALLSYMS`` so
that it produces readable dumps that can be used as-is (this also
produces better output than ksymoops). If for some reason your kernel
is not build with ``CONFIG_KALLSYMS`` and you have no way to rebuild and
reproduce the Oops with that option, then you can still decode that Oops
with ksymoops.
Mkinitrd
--------
These changes to the ``/lib/modules`` file tree layout also require that
mkinitrd be upgraded.
E2fsprogs
---------
The latest version of ``e2fsprogs`` fixes several bugs in fsck and
debugfs. Obviously, it's a good idea to upgrade.
JFSutils
--------
The ``jfsutils`` package contains the utilities for the file system.
The following utilities are available:
- ``fsck.jfs`` - initiate replay of the transaction log, and check
and repair a JFS formatted partition.
- ``mkfs.jfs`` - create a JFS formatted partition.
- other file system utilities are also available in this package.
Xfsprogs
--------
The latest version of ``xfsprogs`` contains ``mkfs.xfs``, ``xfs_db``, and the
``xfs_repair`` utilities, among others, for the XFS filesystem. It is
architecture independent and any version from 2.0.0 onward should
work correctly with this version of the XFS kernel code (2.6.0 or
later is recommended, due to some significant improvements).
PCMCIAutils
-----------
PCMCIAutils replaces ``pcmcia-cs``. It properly sets up
PCMCIA sockets at system startup and loads the appropriate modules
for 16-bit PCMCIA devices if the kernel is modularized and the hotplug
subsystem is used.
Quota-tools
-----------
Support for 32 bit uid's and gid's is required if you want to use
the newer version 2 quota format. Quota-tools version 3.07 and
newer has this support. Use the recommended version or newer
from the table above.
Intel IA32 microcode
--------------------
A driver has been added to allow updating of Intel IA32 microcode,
accessible as a normal (misc) character device. If you are not using
udev you may need to::
mkdir /dev/cpu
mknod /dev/cpu/microcode c 10 184
chmod 0644 /dev/cpu/microcode
as root before you can use this. You'll probably also want to
get the user-space microcode_ctl utility to use with this.
udev
----
``udev`` is a userspace application for populating ``/dev`` dynamically with
only entries for devices actually present. ``udev`` replaces the basic
functionality of devfs, while allowing persistent device naming for
devices.
FUSE
----
Needs libfuse 2.4.0 or later. Absolute minimum is 2.3.0 but mount
options ``direct_io`` and ``kernel_cache`` won't work.
Networking
**********
General changes
---------------
If you have advanced network configuration needs, you should probably
consider using the network tools from ip-route2.
Packet Filter / NAT
-------------------
The packet filtering and NAT code uses the same tools like the previous 2.4.x
kernel series (iptables). It still includes backwards-compatibility modules
for 2.2.x-style ipchains and 2.0.x-style ipfwadm.
PPP
---
The PPP driver has been restructured to support multilink and to
enable it to operate over diverse media layers. If you use PPP,
upgrade pppd to at least 2.4.0.
If you are not using udev, you must have the device file /dev/ppp
which can be made by::
mknod /dev/ppp c 108 0
as root.
NFS-utils
---------
In ancient (2.4 and earlier) kernels, the nfs server needed to know
about any client that expected to be able to access files via NFS. This
information would be given to the kernel by ``mountd`` when the client
mounted the filesystem, or by ``exportfs`` at system startup. exportfs
would take information about active clients from ``/var/lib/nfs/rmtab``.
This approach is quite fragile as it depends on rmtab being correct
which is not always easy, particularly when trying to implement
fail-over. Even when the system is working well, ``rmtab`` suffers from
getting lots of old entries that never get removed.
With modern kernels we have the option of having the kernel tell mountd
when it gets a request from an unknown host, and mountd can give
appropriate export information to the kernel. This removes the
dependency on ``rmtab`` and means that the kernel only needs to know about
currently active clients.
To enable this new functionality, you need to::
mount -t nfsd nfsd /proc/fs/nfsd
before running exportfs or mountd. It is recommended that all NFS
services be protected from the internet-at-large by a firewall where
that is possible.
mcelog
------
On x86 kernels the mcelog utility is needed to process and log machine check
events when ``CONFIG_X86_MCE`` is enabled. Machine check events are errors
reported by the CPU. Processing them is strongly encouraged.
Kernel documentation
********************
Sphinx
------
Please see :ref:`sphinx_install` in Documentation/doc-guide/sphinx.rst
for details about Sphinx requirements.
rustdoc
-------
``rustdoc`` is used to generate the documentation for Rust code. Please see
Documentation/rust/general-information.rst for more information.
Getting updated software
========================
Kernel compilation
******************
gcc
---
- <ftp://ftp.gnu.org/gnu/gcc/>
Clang/LLVM
----------
- :ref:`Getting LLVM <getting_llvm>`.
Rust
----
- Documentation/rust/quick-start.rst.
bindgen
-------
- Documentation/rust/quick-start.rst.
Make
----
- <ftp://ftp.gnu.org/gnu/make/>
Bash
----
- <ftp://ftp.gnu.org/gnu/bash/>
Binutils
--------
- <https://www.kernel.org/pub/linux/devel/binutils/>
Flex
----
- <https://github.com/westes/flex/releases>
Bison
-----
- <ftp://ftp.gnu.org/gnu/bison/>
OpenSSL
-------
- <https://www.openssl.org/>
System utilities
****************
Util-linux
----------
- <https://www.kernel.org/pub/linux/utils/util-linux/>
Kmod
----
- <https://www.kernel.org/pub/linux/utils/kernel/kmod/>
- <https://git.kernel.org/pub/scm/utils/kernel/kmod/kmod.git>
Ksymoops
--------
- <https://www.kernel.org/pub/linux/utils/kernel/ksymoops/v2.4/>
Mkinitrd
--------
- <https://code.launchpad.net/initrd-tools/main>
E2fsprogs
---------
- <https://www.kernel.org/pub/linux/kernel/people/tytso/e2fsprogs/>
- <https://git.kernel.org/pub/scm/fs/ext2/e2fsprogs.git/>
JFSutils
--------
- <https://jfs.sourceforge.net/>
Xfsprogs
--------
- <https://git.kernel.org/pub/scm/fs/xfs/xfsprogs-dev.git>
- <https://www.kernel.org/pub/linux/utils/fs/xfs/xfsprogs/>
Pcmciautils
-----------
- <https://www.kernel.org/pub/linux/utils/kernel/pcmcia/>
Quota-tools
-----------
- <https://sourceforge.net/projects/linuxquota/>
Intel P6 microcode
------------------
- <https://downloadcenter.intel.com/>
udev
----
- <https://www.freedesktop.org/software/systemd/man/udev.html>
FUSE
----
- <https://github.com/libfuse/libfuse/releases>
mcelog
------
- <https://www.mcelog.org/>
Networking
**********
PPP
---
- <https://download.samba.org/pub/ppp/>
- <https://git.ozlabs.org/?p=ppp.git>
- <https://github.com/paulusmack/ppp/>
NFS-utils
---------
- <https://sourceforge.net/project/showfiles.php?group_id=14>
- <https://nfs.sourceforge.net/>
Iptables
--------
- <https://netfilter.org/projects/iptables/index.html>
Ip-route2
---------
- <https://www.kernel.org/pub/linux/utils/net/iproute2/>
OProfile
--------
- <https://oprofile.sf.net/download/>
Kernel documentation
********************
Sphinx
------
- <https://www.sphinx-doc.org/>
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