systemd/man/sd_id128_get_machine.xml

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

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<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>
                <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>

                </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><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_get_boot()</function> always returns
                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 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>
                and <function>sd_id128_get_boot()</function>
                interfaces are available as a shared library, which can
                be compiled and linked to with the
                <literal>libsystemd</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>3</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>random</refentrytitle><manvolnum>4</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>sd_id128_randomize</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                </para>
        </refsect1>

</refentry>