core: add "invocation ID" concept to service manager

[thirdparty/systemd.git] / man / sd_id128_get_machine.xml

<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

<!--
  This file is part of systemd.

  Copyright 2012 Lennart Poettering

  systemd is free software; you can redistribute it and/or modify it
  under the terms of the GNU Lesser General Public License as published by
  the Free Software Foundation; either version 2.1 of the License, or
  (at your option) any later version.

  systemd is distributed in the hope that it will be useful, but
  WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public License
  along with systemd; If not, see <http://www.gnu.org/licenses/>.
-->

<refentry id="sd_id128_get_machine">

  <refentryinfo>
    <title>sd_id128_get_machine</title>
    <productname>systemd</productname>

    <authorgroup>
      <author>
        <contrib>Developer</contrib>
        <firstname>Lennart</firstname>
        <surname>Poettering</surname>
        <email>lennart@poettering.net</email>
      </author>
    </authorgroup>
  </refentryinfo>

  <refmeta>
    <refentrytitle>sd_id128_get_machine</refentrytitle>
    <manvolnum>3</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>sd_id128_get_machine</refname>
    <refname>sd_id128_get_boot</refname>
    <refname>sd_id128_get_invocation</refname>
    <refpurpose>Retrieve 128-bit IDs</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <funcsynopsis>
      <funcsynopsisinfo>#include &lt;systemd/sd-id128.h&gt;</funcsynopsisinfo>

      <funcprototype>
        <funcdef>int <function>sd_id128_get_machine</function></funcdef>
        <paramdef>sd_id128_t *<parameter>ret</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_id128_get_boot</function></funcdef>
        <paramdef>sd_id128_t *<parameter>ret</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_id128_get_invocation</function></funcdef>
        <paramdef>sd_id128_t *<parameter>ret</parameter></paramdef>
      </funcprototype>

    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><function>sd_id128_get_machine()</function> returns the
    machine ID of the executing host. This reads and parses the
    <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>
    file. This function caches the machine ID internally to make
    retrieving the machine ID a cheap operation.</para>

    <para><function>sd_id128_get_boot()</function> returns the boot ID
    of the executing kernel. This reads and parses the
    <filename>/proc/sys/kernel/random/boot_id</filename> file exposed
    by the kernel. It is randomly generated early at boot and is
    unique for every running kernel instance. See
    <citerefentry project='man-pages'><refentrytitle>random</refentrytitle><manvolnum>4</manvolnum></citerefentry>
    for more information. This function also internally caches the
    returned ID to make this call a cheap operation.</para>

    <para><function>sd_id128_get_invocation()</function> returns the invocation ID of the currently executed
    service. In its current implementation, this reads and parses the <varname>$INVOCATION_ID</varname> environment
    variable that the service manager sets when activating a service, see
    <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for details. The
    ID is cached internally. In future a different mechanism to determine the invocation ID may be added.</para>

    <para>Note that <function>sd_id128_get_boot()</function> and <function>sd_id128_get_invocation()</function> always
    return UUID v4 compatible IDs.  <function>sd_id128_get_machine()</function> will also return a UUID v4-compatible
    ID on new installations but might not on older.  It is possible to convert the machine ID into a UUID v4-compatible
    one. For more information, see
    <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>

    <para>For more information about the <literal>sd_id128_t</literal>
    type see
    <citerefentry><refentrytitle>sd-id128</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
  </refsect1>

  <refsect1>
    <title>Return Value</title>

    <para>The two calls return 0 on success (in which case
    <parameter>ret</parameter> is filled in), or a negative
    errno-style error code.</para>
  </refsect1>

  <refsect1>
    <title>Notes</title>

    <para>The <function>sd_id128_get_machine()</function>, <function>sd_id128_get_boot()</function> and
    <function>sd_id128_get_invocation()</function> interfaces are available as a shared library, which can be compiled
    and linked to with the <literal>libsystemd</literal> <citerefentry
    project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> file.</para>
  </refsect1>

  <refsect1>
    <title>See Also</title>

    <para>
      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd-id128</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_id128_randomize</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry project='man-pages'><refentrytitle>random</refentrytitle><manvolnum>4</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>