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
/usr/share/doc/systemd/READMEfor more information.
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, TFTP, Rsync, or Git.
In the following command-line example,
~/kernelbuild directory to obtain kernel 4.8.6:
$ cd ~/kernelbuild $ wget https://www.kernel.org/pub/linux/kernel/v4.x/linux-4.8.6.tar.xz
You should also verify the correctness of the download before trusting it. First grab the signature, then use that to grab the fingerprint of the signing key, then use the fingerprint to obtain the actual signing key:
$ wget https://www.kernel.org/pub/linux/kernel/v4.x/linux-4.8.6.tar.sign $ gpg --list-packets linux-4.8.6.tar.sign $ gpg --recv-keys <fingerprint-from-previous-step>
Note the signature was generated for the tar archive (i.e. extension
.tar), not the compressed
.tar.xz file that you have downloaded. You need to decompress the latter without untarring it. Verify that you have installed, then you can proceed like so:
$ unxz linux-4.8.6.tar.xz $ gpg --verify linux-4.8.6.tar.sign linux-4.8.6.tar
Do not proceed if this does not result in output that includes the string "Good signature".
wget was not used inside the build directory, it will be necessary to move the tarball into it, e.g.
$ mv /path/to/linux-4.8.6.tar.xz ~/kernelbuild/
Unpack the kernel source
Within the build directory, unpack the kernel tarball:
$ tar -xvJf linux-4.8.6.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-4.8.6/ $ make clean && make mrproper
This is the most crucial step in customizing the default kernel to reflect your computer's precise specifications. Kernel configuration is set in its
.config file, which includes the use of Kernel modules.
By setting the options in
.config properly, your kernel and computer will function most efficiently.
You can choose from two options to set your kernel configuration:
- A. Use the default Arch settings from an official kernel (recommended)
- B. Generate a configuration file which matches the currently running kernel's configuration. (useful if you want to customize your kernel settings further)
A. Default Arch configuration
This method will create a
.config file for the custom kernel using the default Arch kernel settings. If a stock Arch kernel is running, you can use the following command inside the custom kernel source directory:
$ zcat /proc/config.gz > .config
Otherwise, the default configuration can be found online in the official Arch Linux kernel package.
makeunder #Compile the kernel, you will be asked to provide answers to every configuration option that has changed between versions. To accept the defaults without being prompted, run
.configfile, do not forget to rename your kernel version "CONFIG_LOCALVERSION" in the new
.configor in the General Setup > Local version - append to kernel release option using one of the user interfaces listed under #Advanced configuration. If you skip this, there is the risk of overwriting one of your existing kernels by mistake.
B. Generated configuration
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 newer hardware, peripherals, or other features.
$ make localmodconfig
There are several tools 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.
nfor disabled, and
mfor enabled as kernel module (loaded when necessary).
Those tools are:
make menuconfig: Command-line ncurses interface superseded 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. You may need to do this multiple times before 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.
$ 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
arch/x86/Makefile(both for 32 and 64 bits, see ) within the kernel source directory:
- Look for
CONFIG_MK8,CONFIG_MPSC,CONFIG_MCORE2,CONFIG_MATOM,CONFIG_GENERIC_CPUthat you have chosen in
Processor type and features > Processor Family
- Change the call cc-options flag from
-march=nativeto the one that you have selected in Processor Family, e.g.
cflags-$(CONFIG_MK8) += $(call cc-option,-march=native). This is probably the best way to compile with
-march=nativeas it works.
- Note: For 32bit Kernels, you need to edit
arch/x86/Makefile_32.cpuinstead and set
-march=nativefor your processor.
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. Once the
.config file has been set for the custom kernel, within the source directory run the following command to compile:
Xis an integer number of parallel jobs. The best results are often achieved using the number of CPU cores in the machine + 1; for example, with a 2-core processor run
make -j3. See Makepkg#Improving compile times for more information.
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 4.8 installed above, they would be copied to
/lib/modules/4.8.6-ARCH. This keeps the modules for individual kernels used separated.
Copy the kernel to /boot directory
bzImagekernel file has been copied from the appropriate directory for your system architecture. See below.
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 4.8 kernel has been copied over and renamed to
- 32-bit (i686) kernel:
# cp -v arch/x86/boot/bzImage /boot/vmlinuz-linux48
- 64-bit (x86_64) kernel:
# cp -v arch/x86_64/boot/bzImage /boot/vmlinuz-linux48
Make initial RAM disk
linux<major revision><minor revision>convention. For example, the name 'linux48' was given as '4' is the major revision and '8' is the minor revision of the 4.8 kernel. This convention will make it easier to maintain multiple kernels, regularly use mkinitcpio, and build third-party modules.
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 4.8, 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/linux48.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-linux48" ... default_image="/boot/initramfs-linux48.img" ... fallback_image="/boot/initramfs-linux48-fallback.img"
Finally, generate the initramfs images for the custom kernel in the same way as for an official kernel:
# mkinitcpio -p linux48
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 4.8 custom kernel installed above would be:
# mkinitcpio -k linux-4.8.6 -g /boot/initramfs-linux48.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
$ arch/x86/boot/install.sh. Remember to type
liloas root at the prompt to update it.