systemd/man/systemd-id128.xml

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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
  "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->

<refentry id="systemd-id128" xmlns:xi="http://www.w3.org/2001/XInclude">

  <refentryinfo>
    <title>systemd-id128</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>systemd-id128</refentrytitle>
    <manvolnum>1</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>systemd-id128</refname>
    <refpurpose>Generate and print sd-128 identifiers</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <cmdsynopsis>
      <command>systemd-id128</command>
      <arg choice="opt" rep="repeat">OPTIONS</arg>
      <arg choice="plain">new</arg>
    </cmdsynopsis>

    <cmdsynopsis>
      <command>systemd-id128</command>
      <arg choice="opt" rep="repeat">OPTIONS</arg>
      <arg choice="plain">machine-id</arg>
    </cmdsynopsis>

    <cmdsynopsis>
      <command>systemd-id128</command>
      <arg choice="opt" rep="repeat">OPTIONS</arg>
      <arg choice="plain">boot-id</arg>
    </cmdsynopsis>

    <cmdsynopsis>
      <command>systemd-id128</command>
      <arg choice="opt" rep="repeat">OPTIONS</arg>
      <arg choice="plain">invocation-id</arg>
    </cmdsynopsis>

    <cmdsynopsis>
      <command>systemd-id128</command>
      <arg choice="opt" rep="repeat">OPTIONS</arg>
      <arg choice="plain">var-partition-uuid</arg>
    </cmdsynopsis>

    <cmdsynopsis>
      <command>systemd-id128</command>
      <arg choice="opt" rep="repeat">OPTIONS</arg>
      <arg choice="plain">show</arg>
      <arg choice="opt" rep="repeat">NAME|UUID</arg>
    </cmdsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><command>id128</command> may be used to conveniently print
    <citerefentry><refentrytitle>sd-id128</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    UUIDs. What identifier is printed depends on the specific verb.</para>

    <para>With <command>new</command>, a new random identifier will be generated.</para>

    <para>With <command>machine-id</command>, the identifier of the current machine will be
    printed. See
    <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
    </para>

    <para>With <command>boot-id</command>, the identifier of the current boot will be
    printed.</para>

    <para>With <command>invocation-id</command>, the identifier of the current service invocation
    will be printed. This is available in systemd services. See
    <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
    </para>

    <para>With <command>show</command>, well-known IDs are printed (for now, only GPT partition type UUIDs),
    along with brief identifier strings. When no arguments are specified, all known IDs are shown. When
    arguments are specified, they may be the identifiers or ID values of one or more known IDs, which are
    then printed with their name, or arbitrary IDs, which are then printed with a placeholder name. Combine
    with <option>--uuid</option> to list the IDs in UUID style, i.e. the way GPT partition type UUIDs are
    usually shown.</para>

    <para><command>machine-id</command>, <command>boot-id</command>, and <command>show</command> may be
    combined with the <option>--app-specific=<replaceable>app-id</replaceable></option> switch to generate
    application-specific IDs. See
    <citerefentry><refentrytitle>sd_id128_get_machine</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    for the discussion when this is useful. Support for <command>show --app-specific=</command> was added in
    version 255.</para>

    <para><command>var-partition-uuid</command> prints a UUID which, following the <ulink
    url="https://uapi-group.org/specifications/specs/discoverable_partitions_specification">Discoverable
    Partitions Specification</ulink>, should be used as the GPT partition UUID for
    <filename>/var/</filename>, being derived from the GPT partition type, keyed by the local
    <filename>/etc/machine-id</filename>. Added in version 257.</para>
  </refsect1>

  <refsect1>
    <title>Options</title>

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

    <variablelist>
      <varlistentry>
        <term><option>-p</option></term>
        <term><option>--pretty</option></term>

        <listitem><para>Generate output as programming language snippets.</para>

        <xi:include href="version-info.xml" xpointer="v240"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>-P</option></term>
        <term><option>--value</option></term>

        <listitem><para>Only print the value. May be combined with
        <option>-u</option>/<option>--uuid</option>.</para>

        <xi:include href="version-info.xml" xpointer="v255"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>-a <replaceable>app-id</replaceable></option></term>
        <term><option>--app-specific=<replaceable>app-id</replaceable></option></term>

        <listitem><para>With this option, identifiers will be printed that are the result of hashing the
        application identifier <replaceable>app-id</replaceable> and another ID. The
        <replaceable>app-id</replaceable> argument must be a valid sd-id128 string identifying the
        application. When used with <command>machine-id</command>, the other ID will be the machine ID as
        described in
        <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>, when
        used with <command>boot-id</command>, the other ID will be the boot ID, and when used with
        <command>show</command>, the other ID or IDs should be specified via the positional arguments.</para>

        <xi:include href="version-info.xml" xpointer="v240"/>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><option>-u</option></term>
        <term><option>--uuid</option></term>

        <listitem><para>Generate output as a UUID formatted in the "canonical representation", with five
        groups of digits separated by hyphens. See the Wikipedia entry for
        <ulink url="https://en.wikipedia.org/wiki/Universally_unique_identifier#Format">Universally Unique Identifiers</ulink>
        for more discussion.</para>

        <xi:include href="version-info.xml" xpointer="v244"/></listitem>
      </varlistentry>

      <xi:include href="standard-options.xml" xpointer="no-pager" />
      <xi:include href="standard-options.xml" xpointer="no-legend" />
      <xi:include href="standard-options.xml" xpointer="json" />
      <xi:include href="standard-options.xml" xpointer="j" />
      <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, and a non-zero failure code otherwise.</para>
  </refsect1>

  <refsect1>
    <title>Examples</title>

    <example>
      <title>Show a well-known UUID</title>
      <programlisting>
$ systemd-id128 show --value user-home
773f91ef66d449b5bd83d683bf40ad16

$ systemd-id128 show --value --uuid user-home
773f91ef-66d4-49b5-bd83-d683bf40ad16

$ systemd-id128 show 773f91ef-66d4-49b5-bd83-d683bf40ad16
NAME      ID
user-home 773f91ef66d449b5bd83d683bf40ad16
</programlisting>
    </example>

    <example>
      <title>Generate an application-specific UUID</title>

      <programlisting>
$ systemd-id128 machine-id -u
3a9d668b-4db7-4939-8a4a-5e78a03bffb7

$ systemd-id128 new -u
1fb8f24b-02df-458d-9659-cc8ace68e28a

$ systemd-id128 machine-id -u -a 1fb8f24b-02df-458d-9659-cc8ace68e28a
47b82cb1-5339-43da-b2a6-1c350aef1bd1

$ systemd-id128 -Pu show 3a9d668b-4db7-4939-8a4a-5e78a03bffb7 \
    -a 1fb8f24b-02df-458d-9659-cc8ace68e28a
47b82cb1-5339-43da-b2a6-1c350aef1bd1
</programlisting>

      <para>On a given machine with the ID 3a9d668b-4db7-4939-8a4a-5e78a03bffb7, for the application
      1fb8f24b-02df-458d-9659-cc8ace68e28a, we generate an application-specific machine ID
      (47b82cb1-5339-43da-b2a6-1c350aef1bd1). If we want to later recreate the same calculation on a
      different machine, we need to specify both IDs explicitly as parameters to <command>show</command>.
      </para>
    </example>
  </refsect1>

  <refsect1>
    <title>See Also</title>
    <para><simplelist type="inline">
      <member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd-id128</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd_id128_get_machine</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
    </simplelist></para>
  </refsect1>

</refentry>