systemd/man/systemd-machine-id-setup.xml

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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="systemd-machine-id-setup"
    xmlns:xi="http://www.w3.org/2001/XInclude">

  <refentryinfo>
    <title>systemd-machine-id-setup</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>systemd-machine-id-setup</refentrytitle>
    <manvolnum>1</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>systemd-machine-id-setup</refname>
    <refpurpose>Initialize the machine ID in /etc/machine-id</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <cmdsynopsis>
      <command>systemd-machine-id-setup</command>
    </cmdsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><command>systemd-machine-id-setup</command> may be used by
    system installer tools to initialize the machine ID stored in
    <filename>/etc/machine-id</filename> at install time, with a
    provisioned or randomly generated ID. See
    <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>
    for more information about this file.</para>

    <para>If the tool is invoked without the <option>--commit</option>
    switch, <filename>/etc/machine-id</filename> is initialized with a
    valid, new machine ID if it is missing or empty. The new machine
    ID will be acquired in the following fashion:</para>

    <orderedlist>
      <listitem><para>If a valid D-Bus machine ID is already
      configured for the system, the D-Bus machine ID is copied and
      used to initialize the machine ID in
      <filename>/etc/machine-id</filename>.</para></listitem>

      <listitem><para>If run inside a KVM virtual machine and a UUID
      is configured (via the <option>-uuid</option>
      option), this UUID is used to initialize the machine ID. The
      caller must ensure that the UUID passed is sufficiently unique
      and is different for every booted instance of the
      VM.</para></listitem>

      <listitem><para>Similarly, if run inside a Linux container environment and a UUID is configured for the
      container, this is used to initialize the machine ID. For details, see the documentation of the <ulink
      url="https://systemd.io/CONTAINER_INTERFACE">Container Interface</ulink>.</para></listitem>

      <listitem><para>Otherwise, a new ID is randomly
      generated.</para></listitem>
    </orderedlist>

    <para>The <option>--commit</option> switch may be used to commit a
    transient machined ID to disk, making it persistent. For details,
    see below.</para>

    <para>Use
    <citerefentry><refentrytitle>systemd-firstboot</refentrytitle><manvolnum>1</manvolnum></citerefentry>
    to initialize the machine ID on mounted (but not booted) system
    images.</para>

  </refsect1>

  <refsect1>
    <title>Options</title>

    <para>The following options are understood:</para>

    <variablelist>

      <varlistentry>
        <term><option>--root=<replaceable>path</replaceable></option></term>
        <listitem><para>Takes a directory path as argument. All paths operated on will be prefixed with the
        given alternate <replaceable>root</replaceable> path, including the path for
        <filename>/etc/machine-id</filename> itself.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--image=<replaceable>path</replaceable></option></term>
        <listitem><para>Takes a path to a device node or regular file as argument. This is similar to
        <option>--root=</option> as described above, but operates on a disk image instead of a directory
        tree.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--commit</option></term>
        <listitem><para>Commit a transient machine ID to disk. This
        command may be used to convert a transient machine ID into a
        persistent one. A transient machine ID file is one that was
        bind mounted from a memory file system (usually
        <literal>tmpfs</literal>) to
        <filename>/etc/machine-id</filename> during the early phase of
        the boot process. This may happen because
        <filename>/etc/</filename> is initially read-only and was
        missing a valid machine ID file at that point.</para>

        <para>This command will execute no operation if
        <filename>/etc/machine-id</filename> is not mounted from a
        memory file system, or if <filename>/etc/</filename> is
        read-only. The command will write the current transient
        machine ID to disk and unmount the
        <filename>/etc/machine-id</filename> mount point in a
        race-free manner to ensure that this file is always valid and
        accessible for other processes.</para>

        <para>This command is primarily used by the
        <citerefentry><refentrytitle>systemd-machine-id-commit.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
        early boot service.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--print</option></term>

        <listitem><para>Print the machine ID generated or committed after the operation is complete.</para></listitem>
      </varlistentry>

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

  </refsect1>

  <refsect1>
    <title>Exit status</title>

    <para>On success, 0 is returned, a non-zero failure code
    otherwise.</para>
  </refsect1>

  <refsect1>
    <title>See Also</title>
    <para>
      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd-machine-id-commit.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
      <citerefentry project='dbus'><refentrytitle>dbus-uuidgen</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd-firstboot</refentrytitle><manvolnum>1</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>