sd_id128_randomize.xml 6.94 KB
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<?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_randomize">

        <refentryinfo>
                <title>sd_id128_randomize</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_randomize</refentrytitle>
                <manvolnum>3</manvolnum>
        </refmeta>

        <refnamediv>
                <refname>sd_id128_randomize</refname>
                <refname>sd_id128_get_machine</refname>
                <refname>sd_id128_get_boot</refname>
                <refpurpose>Generate or retrieve 128 bit IDs</refpurpose>
        </refnamediv>

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

                        <funcprototype>
                                <funcdef>int <function>sd_id128_randomize</function></funcdef>
                                <paramdef>sd_id128_t* <parameter>ret</parameter></paramdef>
                        </funcprototype>

                        <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>

                </funcsynopsis>
        </refsynopsisdiv>

        <refsect1>
                <title>Description</title>

                <para><function>sd_id128_randomize()</function>
                generates a new randomized 128 bit ID and returns it
                in <parameter>ret</parameter>. Every invocation
                returns a new randomly generated ID. This uses the
                <filename>/dev/urandom</filename> kernel random number
                generator.</para>

                <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><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>Note that
                <function>sd_id128_randomize()</function> and
                <function>sd_id128_get_boot()</function> always return
                a UUID v4 compatible
                ID. <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 an 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>7</manvolnum></citerefentry>.</para>

                <para><citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
                <literal>--new-id</literal> command may be used as
                command line front-end for
                <function>sd_id128_randomize()</function>.</para>
        </refsect1>

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

                <para>The three calls returns 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_randomize()</function>,
                <function>sd_id128_get_machine()</function> and
                <function>sd_id128_get_boot()</function> interfaces
                are available as shared library, which can be compiled
                and linked to with the
                <literal>libsystemd-id128</literal>
                <citerefentry><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>7</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>random</refentrytitle><manvolnum>4</manvolnum></citerefentry>
                </para>
        </refsect1>

</refentry>