Void Linux provides many kernel series in the default repository. These are
named linux<x>.<y>: for example, linux4.19. You can query for all available
kernel series by running:
$ xbps-query --regex -Rs '^linux[0-9.]+-[0-9._]+'
The linux meta package, installed by default, depends on one of the kernel
packages, usually the package containing the latest mainline kernel that works
with all DKMS modules. Newer kernels might be available in the repository, but
are not necessarily considered stable enough to be the default; use these at
your own risk. If you wish to use a more recent kernel and have DKMS modules
that you need to build, install the relevant linux<x>.<y>-headers package,
then use xbps-reconfigure(1) to
reconfigure the linux<x>.<y> package you installed. This will build the DKMS
modules.
When updating the kernel, old versions are left behind in case it is necessary
to roll back to an older version. Over time, old kernel versions can accumulate,
consuming disk space and increasing the time taken by DKMS module updates.
Furthermore, if /boot is a separate partition and fills up with old kernels,
updating can fail or result in incomplete initramfs filesystems to be generated
and result in kernel panics if they are being booted. Thus, it may be advisable
to clean old kernels from time to time.
Removing old kernels is done using the
vkpurge(8) utility. vkpurge comes
pre-installed on every Void Linux system. This utility runs the necessary
hooks when removing old kernels. Note that vkpurge does not
remove kernel packages, only particular kernels.
If you've installed a kernel package for a series other than the default, and
want to remove the default kernel packages, use
xbps.d(5) ignorepkg entries to
ignore the relevant
linux<x>.<y> and linux<x>.<y>-headers packages. After adding these entries,
you will be able to remove the packages with
xbps-remove(1).
Kernel modules are typically drivers for devices or filesystems.
Normally the kernel automatically loads required modules, but sometimes it may be necessary to explicitly specify modules to be loaded during boot.
To load kernel modules during boot, a .conf file like
/etc/modules-load.d/virtio.conf needs to be created with the contents:
# load virtio-net
virtio-net
Blacklisting kernel modules is a method for preventing modules from being loaded by the kernel. There are two different methods for blacklisting kernel modules, one for modules loaded by the initramfs and one for modules loaded after the initramfs process is done. Modules loaded by the initramfs have to be blacklisted in the initramfs configuration.
To blacklist modules loaded after the initramfs process, create a .conf file,
like /etc/modprobe.d/radeon.conf, with the contents:
blacklist radeon
After making the necessary changes to the configuration files, the initramfs needs to be regenerated for the changes to take effect on the next boot.
Dracut can be configured to not include kernel modules through a configuration
file. To blacklist modules from being included in a dracut initramfs, create a
.conf file, like /etc/dracut.conf.d/radeon.conf, with the contents:
omit_drivers+=" radeon "
To blacklist modules from being included in a mkinitcpio initramfs a .conf
file needs to be created like /etc/modprobe.d/radeon.conf with the contents:
blacklist radeon
Void Linux provides directories for kernel hooks in
/etc/kernel.d/{pre-install,post-install,pre-remove,post-remove}.
These hooks are used to update the boot menus for bootloaders like grub,
gummiboot and lilo.
The {pre,post}-install hooks are executed by
xbps-reconfigure(1) when
configuring a Linux kernel, such as building its initramfs. This happens when a
kernel series is installed for the first time or updated, but can also be run
manually:
# xbps-reconfigure --force linux<x>.<y>
If run manually, they serve to apply initramfs configuration changes to the next boot.
The {pre,post}-remove hooks are executed by
vkpurge(8) when removing old kernels.
There are kernel modules that are not part of the Linux source tree that are
built at install time using DKMS and kernel hooks. The
available modules can be listed by searching for dkms in the package
repositories.
DKMS build logs are available in /var/lib/dkms/.
The kernel, the initial RAM disk (initrd) and some system programs can be configured at boot by kernel command line arguments. The parameters understood by the kernel are explained in the kernel-parameters documentation and by bootparam(7). Parameters understood by dracut can be found in dracut.cmdline(7).
Once the system is booted, the current kernel command line parameters can be
found in the /proc/cmdline file. Some system programs can change their
behavior based on the parameters passed in the command line, which is what
happens when booting a different
runsvdir, for example.
There are different ways of setting these parameters, some of which are explained below.
Kernel command line arguments can be added through the GRUB bootloader by
editing /etc/default/grub, changing the GRUB_CMDLINE_LINUX_DEFAULT variable
and then running update-grub.
Dracut can be configured to add additional command line arguments to the kernel through a configuration file. The documentation for dracut's configuration files can be found in dracut.conf(5). To apply these changes, it is necessary to regenerate the initramfs.