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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
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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 <systemd/sd-id128.h></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>
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