systemd/man/kernel-install.xml

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<refentry id="kernel-install">

  <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="plain"><replaceable>KERNEL-VERSION</replaceable></arg>
      <arg choice="opt"><replaceable>KERNEL-IMAGE</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 <filename>/boot</filename>.
    </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></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> creates the directory
          <filename>/boot/<replaceable>MACHINE-ID</replaceable>/<replaceable>KERNEL-VERSION</replaceable>/</filename>
          and 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></programlisting>
          </para>

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

          <itemizedlist>

            <listitem><para><filename>50-depmod.install</filename> runs
            <citerefentry><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>.
            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.  If the file
            <filename>initrd</filename> is found next to the kernel image file, the initrd will be added to the
            configuration.</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>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>/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>/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 the file specifies the machine identification <replaceable>MACHINE-ID</replaceable>.</para>
          </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <filename>/etc/os-release</filename>
          <filename>/usr/lib/os-release</filename>
        </term>
          <listitem>
            <para>The content of the file specifies the operating system title <replaceable>PRETTY_NAME</replaceable>.</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><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>