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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->

<refentry id="kernel-install"
          xmlns:xi="http://www.w3.org/2001/XInclude">

  <refentryinfo>
    <title>kernel-install</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>kernel-install</refentrytitle>
    <manvolnum>8</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>kernel-install</refname>
    <refpurpose>Add and remove kernel and initramfs images to and from /boot</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <cmdsynopsis>
      <command>kernel-install</command>
      <arg choice="plain">COMMAND</arg>
      <arg choice="opt" rep="repeat">OPTIONS</arg>
      <arg choice="plain"><replaceable>KERNEL-VERSION</replaceable></arg>
      <arg choice="plain"><replaceable>KERNEL-IMAGE</replaceable></arg>
      <arg choice="opt" rep="repeat"><replaceable>INITRD-FILE</replaceable></arg>
    </cmdsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>
    <para><command>kernel-install</command> is used to install and remove kernel and initramfs images to and
    from the boot loader partition, referred to as <varname>$BOOT</varname> here. It will usually be one of
    <filename>/boot/</filename>, <filename>/efi/</filename>, or <filename>/boot/efi/</filename>, see below.
    </para>

    <para><command>kernel-install</command> will execute the files
    located in the directory <filename>/usr/lib/kernel/install.d/</filename>
    and the local administration directory <filename>/etc/kernel/install.d/</filename>.
    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 <filename>/etc/kernel/install.d/</filename> take precedence over files with the same name
    in <filename>/usr/lib/kernel/install.d/</filename>. This can be used to override a system-supplied
    executables with a local file if needed; a symbolic link in <filename>/etc/kernel/install.d/</filename>
    with the same name as an executable in <filename>/usr/lib/kernel/install.d/</filename>,
    pointing to <filename>/dev/null</filename>, disables the executable entirely. Executables must have the
    extension <literal>.install</literal>; other extensions are ignored.</para>

    <para>An executable should return <constant>0</constant> on success. It may also
    return <constant>77</constant> to cause the whole operation to terminate
    (executables later in lexical order will be skipped).</para>
  </refsect1>

  <refsect1>
    <title>Commands</title>
    <para>The following commands are understood:</para>
    <variablelist>
      <varlistentry>
        <term><command>add <replaceable>KERNEL-VERSION</replaceable> <replaceable>KERNEL-IMAGE</replaceable> [<replaceable>INITRD-FILE</replaceable> ...]</command></term>
        <listitem>
          <para>This command expects a kernel version string and a path to a kernel image file as
          arguments. <command>kernel-install</command> calls the executables from
          <filename>/usr/lib/kernel/install.d/*.install</filename> and
          <filename>/etc/kernel/install.d/*.install</filename> with the following arguments:

          <programlisting>add <replaceable>KERNEL-VERSION</replaceable> <filename>$BOOT/<replaceable>MACHINE-ID</replaceable>/<replaceable>KERNEL-VERSION</replaceable>/</filename> <replaceable>KERNEL-IMAGE</replaceable> [<replaceable>INITRD-FILE</replaceable> ...]</programlisting>
          </para>

          <para>Three default plugins execute the following operations in this case:</para>

          <itemizedlist>
            <listitem><para><filename>00-entry-directory.install</filename> creates the directory
            <filename>$BOOT/<replaceable>MACHINE-ID</replaceable>/<replaceable>KERNEL-VERSION</replaceable>/</filename>
            if <filename>$BOOT/<replaceable>MACHINE-ID</replaceable>/</filename> already exists.
            </para></listitem>

            <listitem><para><filename>50-depmod.install</filename> runs
            <citerefentry project='man-pages'><refentrytitle>depmod</refentrytitle><manvolnum>8</manvolnum></citerefentry> for the
            <replaceable>KERNEL-VERSION</replaceable>.</para></listitem>

            <listitem><para><filename>90-loaderentry.install</filename> copies <replaceable>KERNEL-IMAGE</replaceable>
            to
            <filename>$BOOT/<replaceable>MACHINE-ID</replaceable>/<replaceable>KERNEL-VERSION</replaceable>/linux</filename>.
            If an <replaceable>INITRD-FILE</replaceable> is provided, it also copies <replaceable>INITRD-FILE</replaceable>
            to
            <filename>$BOOT/<replaceable>MACHINE-ID</replaceable>/<replaceable>KERNEL_VERSION</replaceable>/<replaceable>INITRD-FILE</replaceable></filename>.
            It also creates a boot loader entry according to the <ulink
            url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader Specification</ulink> in
            <filename>$BOOT/loader/entries/<replaceable>MACHINE-ID</replaceable>-<replaceable>KERNEL-VERSION</replaceable>.conf</filename>.
            The title of the entry is the <replaceable>PRETTY_NAME</replaceable> parameter specified in
            <filename>/etc/os-release</filename> or <filename>/usr/lib/os-release</filename> (if the former is
            missing), or "Linux <replaceable>KERNEL-VERSION</replaceable>", if unset.</para>

            <para>If the entry directory
            <filename>$BOOT/<replaceable>MACHINE-ID</replaceable>/<replaceable>KERNEL-VERSION</replaceable>/</filename>
            does not exist, this plugin does nothing.</para></listitem>
          </itemizedlist>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><command>remove <replaceable>KERNEL-VERSION</replaceable></command></term>
        <listitem>
          <para>This command expects a kernel version string as single argument. This calls executables from
          <filename>/usr/lib/kernel/install.d/*.install</filename> and
          <filename>/etc/kernel/install.d/*.install</filename> with the following arguments:

          <programlisting>remove <replaceable>KERNEL-VERSION</replaceable> <filename>$BOOT/<replaceable>MACHINE-ID</replaceable>/<replaceable>KERNEL-VERSION</replaceable>/</filename></programlisting>
          </para>

          <para>Afterwards, <command>kernel-install</command> removes the directory
          <filename>$BOOT/<replaceable>MACHINE-ID</replaceable>/<replaceable>KERNEL-VERSION</replaceable>/</filename>
          and its contents.</para>

          <para>Two default plugins execute the following operations in this case:</para>

          <itemizedlist>

            <listitem><para><filename>50-depmod.install</filename> removes the files generated by <command>depmod</command> for this kernel again.</para></listitem>

            <listitem><para><filename>90-loaderentry.install</filename> removes the file
            <filename>$BOOT/loader/entries/<replaceable>MACHINE-ID</replaceable>-<replaceable>KERNEL-VERSION</replaceable>.conf</filename>.</para></listitem>
          </itemizedlist>

        </listitem>
      </varlistentry>

    </variablelist>
  </refsect1>

  <refsect1>
    <title>The <varname>$BOOT</varname> partition</title>
    <para>The partition where the kernels and <ulink url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot
    Loader Specification</ulink> snippets are located is called <varname>$BOOT</varname>.
    <command>kernel-install</command> determines the location of this partition by checking
    <filename>/efi/</filename>, <filename>/boot/</filename>, and <filename>/boot/efi/</filename>
    in turn. The first location where <filename>$BOOT/loader/entries/</filename> or
    <filename>$BOOT/$MACHINE_ID/</filename> exists is used.</para>
  </refsect1>

  <refsect1>
    <title>Options</title>
    <para>The following options are understood:</para>

    <variablelist>
      <varlistentry>
        <term><option>-v</option></term>
        <term><option>--verbose</option></term>
        <listitem>
          <para>Output additional information about operations being performed.</para>
        </listitem>
      </varlistentry>

      <xi:include href="standard-options.xml" xpointer="help" />
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Environment variables</title>

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

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

    <para><varname>KERNEL_INSTALL_MACHINE_ID=</varname> is set for the plugins to the desired <replaceable>MACHINE-ID</replaceable> –
    either 32 hexadecimal characters or the special value <literal>Default</literal>.</para>
    <para><varname>KERNEL_INSTALL_BOOT_ROOT=</varname> 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 overriden by setting <varname>BOOT_ROOT=</varname>.</para>
  </refsect1>

  <refsect1>
    <title>Exit status</title>
    <para>If every executable returns 0 or 77, 0 is returned, and a non-zero failure code otherwise.</para>
  </refsect1>

  <refsect1>
    <title>Files</title>
    <variablelist>
      <varlistentry>
        <term>
          <filename>/usr/lib/kernel/install.d/*.install</filename>
          <filename>/etc/kernel/install.d/*.install</filename>
        </term>
          <listitem>
            <para>Drop-in files which are executed by kernel-install.</para>
          </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <filename>/usr/lib/kernel/cmdline</filename>
          <filename>/etc/kernel/cmdline</filename>
          <filename>/proc/cmdline</filename>
        </term>
          <listitem>
            <para>Read by <filename>90-loaderentry.install</filename>. The content of the file
            <filename>/etc/kernel/cmdline</filename> specifies the kernel command line to use.  If that file does not
            exist, <filename>/usr/lib/kernel/cmdline</filename> is used.  If that also does not exist,
            <filename>/proc/cmdline</filename> is used.</para>
          </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <filename>/etc/kernel/tries</filename>
        </term>
          <listitem>
            <para>Read by <filename>90-loaderentry.install</filename>. 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
            <filename>$BOOT/loader/entries/<replaceable>MACHINE-ID</replaceable>-<replaceable>KERNEL-VERSION</replaceable>+<replaceable>TRIES</replaceable>.conf</filename>. This
            is useful for boot loaders such as
            <citerefentry><refentrytitle>systemd-boot</refentrytitle><manvolnum>7</manvolnum></citerefentry> which
            implement boot attempt counting with a counter embedded in the entry file name.</para>
          </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <filename>/etc/machine-id</filename>
        </term>
          <listitem>
            <para>The content of this file specifies the machine identification
            <replaceable>MACHINE-ID</replaceable>. If <filename>/etc/machine-id</filename>
            cannot be read or is temporary (backed by a file on <constant>tmpfs</constant>),
            <command>kernel-install</command> will use <literal>Default</literal> instead.</para>
          </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <filename>/etc/os-release</filename>
          <filename>/usr/lib/os-release</filename>
        </term>
          <listitem>
            <para>Read by <filename>90-loaderentry.install</filename>.
            If available, <varname>PRETTY_NAME</varname> is read from these files and used as the title of the boot menu entry.
            Otherwise, <literal>Linux <replaceable>KERNEL-VERSION</replaceable></literal> will be used.</para>
          </listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>See Also</title>
    <para>
      <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>os-release</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry project='man-pages'><refentrytitle>depmod</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd-boot</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
      <ulink url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader Specification</ulink>
    </para>
  </refsect1>

</refentry>
