# Kernels/Compilation/Arch Build System

The Arch Build System can be used to build a custom kernel based on the official linux package. This compilation method can automate the entire process, and is based on a very well tested package. You can edit the PKGBUILD to use a custom kernel configuration or add additional patches.

## Getting the Ingredients

    # pacman -S abs base-devel

First of all, you need a clean kernel to start your customization from. Fetch the kernel package files from ABS:

    $ ABSROOT=. abs core/linux

If you have some problem with the firewall blocking the rsync port, you can try with -t, which uses the tarball to sync.

    $ ABSROOT=. abs core/linux -t

Then, get any other file you need (e.g. custom configuration files, patches, etc.) from the respective sources.

## Modifying the PKGBUILD

Modify `pkgbase` for your custom package name, e.g.:

     pkgbase=linux-custom

### Changing build()

If you need to change a few config options you can use the default one and append your options to the config file:

    $ echo '
    CONFIG_DEBUG_INFO=y
    CONFIG_FOO=n
    ' >> config.x86_64

Or you can use GUI tool to tweak the options. Uncomment one of the possibilities shown in the build() function of the PKGBUILD, e.g.:

    PKGBUILD

    ...
      # 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, uncommenting one of the interactive config tools, such as `nconfig`, and loading your `.config` from there avoids any problems with kernel naming that may otherwise occur - except in the case of at least make menuconfig. See note.

Note: If you uncomment and use 'make menuconfig' in build(), then use the menuconfig gui to load your existing config, you will run into problems with conflicting files in the end package. This is because you will overwrite the default config that PKGBUILD has modified to provide a unique install path, specifically the LOCALVERSION and LOCALVERSION_AUTO config options. To fix this, simply re-set LOCALVERSION to your custom kernel naming and LOCALVERSION_AUTO=n while still in menuconfig. For details, see https://bbs.archlinux.org/viewtopic.php?id=173504
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. But do not use this for custom patches; put your patch commands after these lines. If you do patch manually bztar unpack and replace your patch.

## Compiling

Tip: Running compilation jobs simultaneously can reduce compilation time significantly on multi-core systems.

You can now proceed to compile you kernel by the usual command `makepkg` If you have chosen an interactive 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. On recent systems with a SSD it usually takes less than ten minutes.

## Installing

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-headers_package>
    # pacman -U <kernel_package>

Note: best practice is to install first kernel headers as their will be needed if you want your nvidia driver be included with the nvidia-hook

## Boot Loader

Now, the folders and files for your custom kernel have been created, e.g. `/boot/vmlinuz-linux-test`. To test your kernel, update your bootloader (grub-mkconfig 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 to choose from.

Category:

- Kernel