This article is an introduction to building custom kernels from kernel.org sources. This method of compiling kernels is the traditional method common to all distributions. It can be, depending on your background, more complicated than using the Kernels/Arch Build System. Consider the Arch Build System tools are developed and maintained to make repeatable compilation tasks efficient and safe.
- 1 Preparation
- 2 Configuration
- 3 Compilation and installation
- 4 Bootloader configuration
It is not necessary (or recommended) to use the root account or root privileges (i.e. via Sudo) for kernel preparation.
Install the core packages
Install the PKGBUILD: , , , ,package group, which contains necessary packages such as and . It is also recommended to install the following packages, as listed in the default Arch kernel
Create a kernel compilation directory
It is recommended to create a separate build directory for your kernel(s). In this example, the directory
kernelbuild will be created in the
$ mkdir ~/kernelbuild
Download the kernel source
Download the kernel source from http://www.kernel.org. This should be the tarball (
tar.xz) file for your chosen kernel. It can be downloaded by simply right-clicking the
tar.xz link in your browser and selecting
Save Link As..., or any other number of ways via alternative graphical or command-line tools that utilise HTTP, FTP, RSYNC, or Git. In the following command-line example, has been installed and is used inside the
~/kernelbuild directory to obtain kernel 3.18:
$ cd ~/kernelbuild $ wget https://kernel.org/pub/linux/kernel/v3.x/linux-3.18.28.tar.xz
wget was not used inside the build directory, it will be necessary to move the tarball into it, e.g.
$ mv /path/to/linux-3.18.28.tar.xz ~/kernelbuild/
Unpack the kernel source
Within the build directory, unpack the kernel tarball:
$ tar -xvJf linux-3.18.28.tar.xz
To finalise the preparation, ensure that the kernel tree is absolutely clean; do not rely on the source tree being clean after unpacking. To do so, first change into the new kernel source directory created, and then run the
make mrproper command:
$ cd linux-3.18.28 $ make clean && make mrproper
This is the most crucial step in customizing the kernel to reflect your computer's precise specifications. Kernel configuration is set in its
.config file, which includes the use of the Kernel modules. By setting the options in
.config properly, your kernel and computer will function most efficiently. Note that - again - it is not necessary to use the root account or root privileges for this stage.
Two options are available for ease and to save time:
- Use the default Arch settings from an official kernel (recommended)
- Generate a configuration file by the modules and settings in use by a running kernel at that time.
Default Arch settings
This method will create a
.config file for the custom kernel using the default Arch kernel settings. Ensure that a stock Arch kernel is running and use the following command inside the custom kernel source directory:
$ zcat /proc/config.gz > .config
Generated configuration file
Since kernel 2.6.32, the
localmodconfig command will create a
.config file for the custom kernel by disabling any and all options not currently in use by the running kernel at the time. In other words, it will only enable the options currently being used.
While this minimalist approach will result in a highly streamlined and efficient configuration tailored specifically for your system, there are drawbacks, such as the potential inability of the kernel to support new hardware, peripherals, or other features. Again, ensure that all devices you expect to use have been connected to (and detected by) your system before running the following command:
$ make localmodconfig
There are several interfaces available to fine-tune the kernel configuration, which provide an alternative to otherwise spending hours manually configuring each and every one of the options available during compilation. They are:
make menuconfig: Old command-line ncurses interface superceded by
make nconfig: Newer ncurses interface for the command-line
make xconfig: User-friendly graphical interface that requires to be installed as a dependency. This is the recommended method - especially for less experienced users - as it is easier to navigate, and information about each option is also displayed.
make gconfig: Graphical configuration similar to xconfig but using gtk.
The chosen method should be run inside the kernel source directory, and all will either create a new
.config file, or overwrite an existing one where present. All optional configurations will be automatically enabled, although any newer configuration options (i.e. with an older kernel
.config) may not be automatically selected.
Once the changes have been made save the
.config file. It is a good idea to make a backup copy outside the source directory since you could be doing this multiple times until you get all the options right. If unsure, only change a few options between compilations. If you cannot boot your newly built kernel, see the list of necessary config items here. Running
$ lspci -k # from liveCD lists names of kernel modules in use. Most importantly, you must maintain CGROUPS support. This is necessary for systemd.
Compilation and installation
Compile the kernel
Compilation time will vary from as little as fifteen minutes to over an hour, depending on your kernel configuration and processor capability. See Makeflags for details. Once the
.config file has been set for the custom kernel, within the source directory run the following command to compile:
Compile the modules
Once the kernel has been compiled, the modules for it must follow. As root or with root privileges, run the following command to do so:
# make modules_install
This will copy the compiled modules into
/lib/modules/<kernel version>-<config local version>. For example, for kernel version 3.18 installed above, they would be copied to
/lib/modules/3.18.28-ARCH. This keeps the modules for individual kernels used separated.
Copy the kernel to /boot directory
The kernel compilation process will generate a compressed
bzImage (big zImage) of that kernel, which must be copied to the
/boot directory and renamed in the process. Provided the name is prefixed with
vmlinuz-, you may name the kernel as you wish. In the examples below, the installed and compiled 3.18 kernel has been copied over and renamed to
- 32-bit (i686) kernel:
# cp -v arch/x86/boot/bzImage /boot/vmlinuz-linux318
- 64-bit (x86_64) kernel:
# cp -v arch/x86_64/boot/bzImage /boot/vmlinuz-linux318
Make initial RAM disk
Automated preset method
An existing mkinitcpio preset can be copied and modified so that the custom kernel initramfs images can be generated in the same way as for an official kernel. This is useful where intending to recompile the kernel (e.g. where updated). In the example below, the preset file for the stock Arch kernel will be copied and modified for kernel 3.18, installed above.
First, copy the existing preset file, renaming it to match the name of the custom kernel specified as a suffix to
/boot/vmlinuz- when copying the
bzImage (in this case,
# cp /etc/mkinitcpio.d/linux.preset /etc/mkinitcpio.d/linux318.preset
Second, edit the file and amend for the custom kernel. Note (again) that the
ALL_kver= parameter also matches the name of the custom kernel specified when copying the
... ALL_kver="/boot/vmlinuz-linux318" ... default_image="/boot/initramfs-linux318.img" ... fallback_image="/boot/initramfs-linux318-fallback.img"
Finally, generate the initramfs images for the custom kernel in the same way as for an official kernel:
# mkinitcpio -p linux318
Rather than use a preset file, mkinitcpio can also be used to generate an initramfs file manually. The syntax of the command is:
# mkinitcpio -k <kernelversion> -g /boot/initramfs-<file name>.img
-k(--kernel <kernelversion>): Specifies the modules to use when generating the initramfs image. The
<kernelversion>name will be the same as the name of the custom kernel source directory (and the modules directory for it, located in
-g(--generate <filename>): Specifies the name of the initramfs file to generate in the
/bootdirectory. Again, using the naming convention mentioned above is recommended.
For example, the command for the 3.18 custom kernel installed above would be:
# mkinitcpio -k linux-3.18.28 -g /boot/initramfs-linux318.img
System.map file is not required for booting Linux. It is a type of "phone directory" list of functions in a particular build of a kernel. The
System.map contains a list of kernel symbols (i.e function names, variable names etc) and their corresponding addresses. This "symbol-name to address mapping" is used by:
- Some processes like klogd, ksymoops etc
- By OOPS handler when information has to be dumped to the screen during a kernel crash (i.e info like in which function it has crashed).
/boot is on a filesystem which supports symlinks (i.e., not FAT32), copy
/boot, appending your kernel's name to the destination file. Then create a symlink from
/boot/System.map to point to
# cp System.map /boot/System.map-YourKernelName # ln -sf /boot/System.map-YourKernelName /boot/System.map
After completing all steps above, you should have the following 3 files and 1 soft symlink in your
/boot directory along with any other previously existing files:
- System Map:
- System Map kernel symlink