kernel-install - Man Page

Add and remove kernel and initramfs images to and from /boot

Synopsis

kernel-install COMMAND [Options...] KERNEL-VERSION KERNEL-IMAGE [INITRD-FILE...]

Description

kernel-install is used to install and remove kernel and initramfs images to and from the boot loader partition, referred to as $BOOT here. It will usually be one of /boot/, /efi/, or /boot/efi/, see below.

kernel-install will execute the files located in the directory /usr/lib/kernel/install.d/ and the local administration directory /etc/kernel/install.d/. All files are collectively sorted and executed in lexical order, regardless of the directory in which they live. However, files with identical filenames replace each other. Files in /etc/kernel/install.d/ take precedence over files with the same name in /usr/lib/kernel/install.d/. This can be used to override a system-supplied executables with a local file if needed; a symbolic link in /etc/kernel/install.d/ with the same name as an executable in /usr/lib/kernel/install.d/, pointing to /dev/null, disables the executable entirely. Executables must have the extension ".install"; other extensions are ignored.

An executable should return 0 on success. It may also return 77 to cause the whole operation to terminate (executables later in lexical order will be skipped).

Commands

The following commands are understood:

add KERNEL-VERSION KERNEL-IMAGE [INITRD-FILE ...]

This command expects a kernel version string and a path to a kernel image file as arguments. kernel-install calls the executables from /usr/lib/kernel/install.d/*.install and /etc/kernel/install.d/*.install with the following arguments:

add KERNEL-VERSION $BOOT/MACHINE-ID/KERNEL-VERSION/ KERNEL-IMAGE [INITRD-FILE ...]

Two default plugins execute the following operations in this case:

  • kernel-install creates $BOOT/MACHINE-ID/KERNEL-VERSION, if enabled (see $KERNEL_INSTALL_LAYOUT=).
  • 50-depmod.install runs depmod(8) for the KERNEL-VERSION.
  • 90-loaderentry.install copies KERNEL-IMAGE to $BOOT/MACHINE-ID/KERNEL-VERSION/linux. If INITRD-FILEs are provided, it also copies them to $BOOT/MACHINE-ID/KERNEL_VERSION/INITRD-FILE. It also creates a boot loader entry according to the Boot Loader Specification[1] in $BOOT/loader/entries/MACHINE-ID-KERNEL-VERSION.conf. The title of the entry is the PRETTY_NAME parameter specified in /etc/os-release or /usr/lib/os-release (if the former is missing), or "Linux KERNEL-VERSION", if unset.

    If $KERNEL_INSTALL_LAYOUT= is not "bls", this plugin does nothing.

remove KERNEL-VERSION

This command expects a kernel version string as single argument. This calls executables from /usr/lib/kernel/install.d/*.install and /etc/kernel/install.d/*.install with the following arguments:

remove KERNEL-VERSION $BOOT/MACHINE-ID/KERNEL-VERSION/

Afterwards, kernel-install removes the directory $BOOT/MACHINE-ID/KERNEL-VERSION/ and its contents.

Two default plugins execute the following operations in this case:

  • 50-depmod.install removes the files generated by depmod for this kernel again.
  • 90-loaderentry.install removes the file $BOOT/loader/entries/MACHINE-ID-KERNEL-VERSION.conf.
  • kernel-install removes $BOOT/MACHINE-ID/KERNEL-VERSION, if enabled (see $KERNEL_INSTALL_LAYOUT=).

The $Boot Partition

The partition where the kernels and Boot Loader Specification[1] snippets are located is called $BOOT. kernel-install determines the location of this partition by checking /efi/, /boot/, and /boot/efi/ in turn. The first location where $BOOT/loader/entries/ or $BOOT/$MACHINE_ID/ exists is used.

Options

The following options are understood:

-v,  --verbose

Output additional information about operations being performed.

-h,  --help

Print a short help text and exit.

Environment Variables

If --verbose is used, $KERNEL_INSTALL_VERBOSE=1 will be set for the plugins. They may output additional logs in this case.

If MACHINE_ID= is set and not empty, it will be used as MACHINE-ID, overriding any automatic detection attempts. The value must be a valid machine ID (32 hexadecimal characters).

KERNEL_INSTALL_MACHINE_ID= is set for the plugins to the desired MACHINE-ID – either 32 hexadecimal characters or the special value "Default".

KERNEL_INSTALL_BOOT_ROOT= is set for the plugins to the root directory (mount point, usually) of the hierarchy where boot-loader entries, kernel images, and associated resources should be placed. Can be overridden by setting BOOT_ROOT=.

KERNEL_INSTALL_LAYOUT=bls|other|... specifies the installation layout. Defaults to bls if $BOOT/MACHINE-ID exists, or other otherwise. Additional layout names may be defined by convention. If a plugin uses a special layout, it's encouraged to declare its own layout name and configure layout= in install.conf upon initial installation.

bls

Standard Boot Loader Specification[1] layout, compatible with systemd-boot(7): entries in $BOOT/loader/entries/MACHINE-ID-KERNEL-VERSION[+TRIES].conf, kernel and initrds under $BOOT/MACHINE-ID/KERNEL-VERSION/

Provided by 90-loaderentry.install.

other

Some other layout not understood natively by kernel-install.

Exit Status

If every executable returns 0 or 77, 0 is returned, and a non-zero failure code otherwise.

Files

/usr/lib/kernel/install.d/*.install /etc/kernel/install.d/*.install

Drop-in files which are executed by kernel-install.

/usr/lib/kernel/cmdline /etc/kernel/cmdline /proc/cmdline

Read by 90-loaderentry.install. The content of the file /etc/kernel/cmdline specifies the kernel command line to use. If that file does not exist, /usr/lib/kernel/cmdline is used. If that also does not exist, /proc/cmdline is used.

/etc/kernel/tries

Read by 90-loaderentry.install. If this file exists a numeric value is read from it and the naming of the generated entry file is slightly altered to include it as $BOOT/loader/entries/MACHINE-ID-KERNEL-VERSION+TRIES.conf. This is useful for boot loaders such as systemd-boot(7) which implement boot attempt counting with a counter embedded in the entry file name.

/etc/machine-id

The content of this file specifies the machine identification MACHINE-ID. If /etc/machine-id cannot be read or is temporary (backed by a file on tmpfs), kernel-install will use "Default" instead.

/etc/machine-info

If this file contains the KERNEL_INSTALL_MACHINE_ID variable, kernel-install will use it as MACHINE-ID instead of the contents of /etc/machine-id. If the variable is not found in /etc/machine-info, kernel-install will try to save the machine ID it uses to install to $BOOT to this file.

/etc/os-release /usr/lib/os-release

Read by 90-loaderentry.install. If available, PRETTY_NAME is read from these files and used as the title of the boot menu entry. Otherwise, "Linux KERNEL-VERSION" will be used.

/usr/lib/kernel/install.conf /etc/kernel/install.conf

Configuration options for kernel-install, as a series of KEY=VALUE assignments, compatible with shell syntax. See the Environment variables section for supported keys.

See Also

machine-id(5), os-release(5), depmod(8), systemd-boot(7), Boot Loader Specification[1]

Notes

1.

Boot Loader Specification
https://systemd.io/BOOT_LOADER_SPECIFICATION

Referenced By

bootctl(1), grubby(8), systemd-boot(7), systemd.directives(7), systemd-firstboot(1), systemd.index(7).

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