Difference between revisions of "Kernel Compilation"

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[[Category:Kernel (English)]]
#REDIRECT [[Kernels#Compilation]]
{{i18n|Kernel Compilation}}
Arch Linux provides for several methods of kernel compilation. Using the [[Arch Build System]] is recommended to take advantage of the high quality of the existing {{Package Official|linux}} [[PKGBUILD]] and the benefits of [[Wikipedia:Package management system|package management]].
==Using the [[Arch Build System]]==
For quite some time, various methods have been proposed to easily build a custom kernel from the -ARCH one. Search the Wiki for a few examples. All these were intelligent ideas, but suffered from [https://bugs.archlinux.org/task/12384 some drawbacks] and were not officially supported by the devs.
On the contrary, the method described in this article should be more solid and safe, and builds on the official {{Package Official|linux}} package.
===Install ABS===
{{Cli|# pacman -S abs base-devel}}
To get the whole tree run:
{{Cli|# abs}}
See [[Arch Build System]] for more information.
===Getting the Ingredients===
First of all, you need a clean kernel to start your customization from. In this article I will assume that you use the official kernel package. So create a folder you want to work in and get the kernel package files from ABS (after syncing):
{{Codeline|cp /var/abs/core/linux/* <working_dir>/}}
Then, get any other file you need (e.g. custom configuration files, patches, etc.) from the respective sources.
===Modifying the PKGBUILD===
Modify the PKGBUILD of the official linux package.
====Changing pkgname====
The first lines will look like this:
# $Id: PKGBUILD 130991 2011-07-09 12:23:51Z thomas $
# Maintainer: Tobias Powalowski <tpowa@archlinux.org>
# Maintainer: Thomas Baechler <thomas@archlinux.org>
pkgname=('linux' 'linux-headers' 'linux-docs') # Build stock -ARCH kernel
# pkgname=linux-custom      # Build kernel with a different name
As you see, there is a commented line for building a kernel with a different name. All you need to do here is to uncomment that line, change the suffix '-custom' to your needs, and comment the standard line. For instance, your file could become:
#pkgname=('linux' 'linux-headers' 'linux-docs') # Build stock -ARCH kernel
pkgname=linux-test      # Build kernel with a different name
{{Note|This assumes that you do not need to recompile linux-headers, -manpages or -docs. If you do, change all three strings accordingly.}}
Now, all the variables of your package will be changed according to the new name. For instance, after installing the package the modules will be located at {{Filename|/lib/modules/<kernel_release>-test/}}.
====Changing build()====
You probably need a custom .config file for your kernel. You can uncomment one of the possibilities shown in the build() function of the PKGBUILD, e.g.:
  # load configuration
  # Configure the kernel. Replace the line below with one of your choice.
  #make menuconfig # CLI menu for configuration
  make nconfig # new CLI menu for configuration
  #make xconfig # X-based configuration
  #make oldconfig # using old config from previous kernel version
  # ... or manually edit .config
If you have already a kernel config file, I suggest to uncomment one interactive config tool, such as nconfig, and load your config from there. This avoids problems with kernel naming I have met with other methods.
{{Note|If you uncomment ''return 1'', you can change to the kernel source directory after makepkg finishes extraction and then make nconfig. This lets you configure the kernel over multiple sessions. When you're ready to compile, copy the .config file over top of either config or config.x86_64 (depending on your architecture), comment ''return 1'' and use '''makepkg -i'''.}}
====Changing the package_linux() function====
Now, you have to write a custom function to tell your system how to install the package. This is most easily done by changing the name of the package_linux() function to package_linux-test(), and adapting the instructions to your needs. If you have no particular needs, your package_linux-test() should look like this:
package_linux-test() {
pkgdesc="The Linux Kernel and modules"
===Compiling with multiple CPUs===
To tell the compiler to use all CPUs during compile use the -j<number> make flag. The number should be n+1 where n is the number of your CPUs.
This example is for a 2 core system (2+1=3):
#-- Make Flags: change this for DistCC/SMP systems
Now you can proceed to compile you kernel by the usual command
If you have chosen an inteactive program for configuring the kernel parameters (like menuconfig), you need to be there during the compilation.
{{Note|A kernel needs some time to be compiled. 1h is not unusual.}}
After the makepkg, you can have a look at the linux.install file. You will see that some variables have changed. Now, you only have to install the package as usual with pacman (or equivalent program):
# pacman -U <kernel_package>
===Boot Loader===
Now, the folders and files for your custom kernel have been created, e.g. {{Filename|/boot/vmlinuz-linux-test}}. To test your kernel, update your bootloader (/boot/grub/menu.lst for GRUB) and add new entries ('default' and 'fallback') for your custom kernel. That way, you can have both the stock kernel and the custom one in parallel.
===Nvidia proprietary driver===
See [[NVIDIA#Alternate_install: custom kernel]].
==Using the [[AUR]]==
There are in the AUR some packages for famous kernel flavors. You can install them 'as is', or use them as a basis for your custom kernel instead of the official -ARCH one.
[[Kernels#Found in the AUR]]
[[Kernel Compilation without ABS|The traditional way]] is simple and straightforward.
This method involves manually downloading a source tarball, and building in your home directory as normal user. Once configured, two compilation/installation methods are offered; the traditional manual method as well as makepkg/pacman.
If you are new to the process, [[Kernel Compilation without ABS for New Users|the traditional way for new users]] may be appropriate.
==See also==
*[http://www.kroah.com/lkn/ O'Reilly - Linux Kernel in a Nutshell] (free ebook)

Revision as of 19:59, 21 February 2012