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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"

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<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>