kernel-install

systemd
kernel-install 8
kernel-install Add and remove kernel and initramfs images to and from /boot
`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 run the executable files ("plugins") 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 placed in these directories 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. Optionally, one or more initial RAM disk images may be specified as well (note that plugins might generate additional ones). `kernel-install` calls the executable files from `/usr/lib/kernel/install.d/*.install` and `/etc/kernel/install.d/*.install` (i.e. the plugins) with the following arguments:

      add KERNEL-VERSION $BOOT/ENTRY-TOKEN/KERNEL-VERSION/ KERNEL-IMAGE [INITRD-FILE ...]

  The third argument directly refers to the path where to place kernel images, initial RAM disk images and other resources for Boot Loader Specification Type #1 entries (the "entry directory"). If other boot loader schemes are used the parameter may be ignored. The ENTRY-TOKEN string is typically the machine ID and is supposed to identify the local installation on the system. For details see below.

  Two default plugins execute the following operations in this case:

  - `kernel-install` creates `$BOOT/ENTRY-TOKEN/KERNEL-VERSION`, if enabled (see `$KERNEL_INSTALL_LAYOUT`).

  - `50-depmod.install` runs depmod 8 for the KERNEL-VERSION.

  - `90-loaderentry.install` copies KERNEL-IMAGE to `$BOOT/ENTRY-TOKEN/KERNEL-VERSION/linux`. If INITRD-FILEs are provided, it also copies them to `$BOOT/ENTRY-TOKEN/KERNEL_VERSION/INITRD-FILE`. It also creates a boot loader entry according to the Boot Loader Specification (Type #1) in `$BOOT/loader/entries/ENTRY-TOKEN-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/ENTRY-TOKEN/KERNEL-VERSION/

  Afterwards, `kernel-install` removes the entry directory `$BOOT/ENTRY-TOKEN/KERNEL-VERSION/` and its contents, if it exists.

  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/ENTRY-TOKEN-KERNEL-VERSION.conf`.

`inspect`

  Shows the various paths and parameters configured or auto-detected. In particular shows the values of the various `$KERNEL_INSTALL_*` environment variables listed below.

## The `$BOOT` partition

The partition where the kernels and Boot Loader Specification 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/ENTRY-TOKEN/` exists is used.

## Options

The following options are understood:

`-v`
`--verbose`

  Output additional information about operations being performed.

## 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 when `kernel-install` is invoked, it will be used as MACHINE-ID, overriding any automatic detection attempts. The value must be a valid machine ID (32 hexadecimal characters).

`$KERNEL_INSTALL_MACHINE_ID` is set for the plugins to the desired MACHINE-ID to use. It's always a 128bit ID, and typically the ID from `/etc/machine-id` or the one passed in via `$MACHINE_ID`. (If no machine ID was specified via these methods it might be generated randomly by `kernel-install`, in which case it only applies to this invocation.)

`$KERNEL_INSTALL_ENTRY_TOKEN` is set for the plugins to the desired entry "token" to use. It's an identifier that shall be used to identify the local installation, and is often the machine ID, i.e. same as `$KERNEL_INSTALL_MACHINE_ID`, but might also be a different type of identifier, for example a fixed string or the `ID=`, `IMAGE_ID=` values from `/etc/os-release`. The string passed here will be used to name Boot Loader Specification entries, or the directories the kernel image and initial RAM disk images are placed into. Note that while oftentimes `$KERNEL_INSTALL_ENTRY_TOKEN` and `$KERNEL_INSTALL_MACHINE_ID` are set to the same value, the latter is guaranteed to be a valid 32 character ID in lowercase hexadecimals while the former can be any short string. The entry token to use is read from `/etc/kernel/entry-token`, if it exists. Otherwise a few possible candidates below the `$BOOT` are searched for Boot Loader Specification Type 1 entry directories, and if found the entry token is derived from that. If that is not successful the machine ID is used as fallback.

`$KERNEL_INSTALL_BOOT_ROOT` is set for the plugins to the absolute path of the root directory (mount point, usually) of the hierarchy where boot loader entries, kernel images, and associated resources should be placed. This usually is the path where the XBOOTLDR partition or the ESP (EFI System Partition) are mounted, and also conceptually referred to as `$BOOT`. Can be overridden by setting `$BOOT_ROOT`.

`$KERNEL_INSTALL_LAYOUT=bls|other|...` is set for the plugins to specify the installation layout. Defaults to `bls` if `$BOOT/ENTRY-TOKEN` 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. The following values are currently understood:

bls

  Standard Boot Loader Specification Type #1 layout, compatible with systemd-boot 7: entries in `$BOOT/loader/entries/ENTRY-TOKEN-KERNEL-VERSION[+TRIES].conf`, kernel and initrds under `$BOOT/ENTRY-TOKEN/KERNEL-VERSION/`

  Implemented by `90-loaderentry.install`.

other

  Some other layout not understood natively by `kernel-install`.

`$KERNEL_INSTALL_INITRD_GENERATOR` is set for plugins to select the initrd generator. This may be configured as `initrd_generator=` in `install.conf`. See below.

`$KERNEL_INSTALL_STAGING_AREA` is set for plugins to a path to a directory. Plugins may drop files in that directory, and they will be installed as part of the loader entry, based on the file name and extension.

## 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/kernel/entry-token`

  If this file exists it is read and used as "entry token" for this system, i.e. is used for naming Boot Loader Specification entries, see `$KERNEL_INSTALL_ENTRY_TOKEN` above for details.

`/etc/machine-id`

  The content of this file specifies the machine identification MACHINE-ID.

`/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. This currently supports two keys: `layout=` and `initrd_generator=`, for details see the Environment variables section above.

## See Also

machine-id 5, os-release 5, depmod 8, systemd-boot 7, Boot Loader Specification