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282 lines
13 KiB
XML
282 lines
13 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refentry id="sd_id128_get_machine" xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_id128_get_machine</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_id128_get_machine</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sd_id128_get_machine</refname>
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<refname>sd_id128_get_app_specific</refname>
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<refname>sd_id128_get_machine_app_specific</refname>
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<refname>sd_id128_get_boot</refname>
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<refname>sd_id128_get_boot_app_specific</refname>
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<refname>sd_id128_get_invocation</refname>
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<refpurpose>Retrieve 128-bit IDs</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <systemd/sd-id128.h></funcsynopsisinfo>
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<funcprototype>
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<funcdef>int <function>sd_id128_get_machine</function></funcdef>
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<paramdef>sd_id128_t *<parameter>ret</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_id128_get_app_specific</function></funcdef>
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<paramdef>sd_id128_t <parameter>base</parameter></paramdef>
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<paramdef>sd_id128_t <parameter>app_id</parameter></paramdef>
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<paramdef>sd_id128_t *<parameter>ret</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_id128_get_machine_app_specific</function></funcdef>
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<paramdef>sd_id128_t <parameter>app_id</parameter></paramdef>
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<paramdef>sd_id128_t *<parameter>ret</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_id128_get_boot</function></funcdef>
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<paramdef>sd_id128_t *<parameter>ret</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_id128_get_boot_app_specific</function></funcdef>
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<paramdef>sd_id128_t <parameter>app_id</parameter></paramdef>
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<paramdef>sd_id128_t *<parameter>ret</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_id128_get_invocation</function></funcdef>
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<paramdef>sd_id128_t *<parameter>ret</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><function>sd_id128_get_machine()</function> returns the machine ID of the executing host. This reads and
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parses the <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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file. This function caches the machine ID internally to make retrieving the machine ID a cheap operation. This ID
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may be used wherever a unique identifier for the local system is needed. However, it is recommended to use this ID
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as-is only in trusted environments. In untrusted environments it is recommended to derive an application specific
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ID from this machine ID, in an irreversible (cryptographically secure) way. To make this easy
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<function>sd_id128_get_machine_app_specific()</function> is provided, see below.</para>
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<para><function>sd_id128_get_app_specific()</function> returns a machine ID that is a combination of the
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<parameter>base</parameter> and <parameter>app_id</parameter> parameters. Internally, this function
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calculates HMAC-SHA256 of the <parameter>app_id</parameter> parameter keyed by the
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<parameter>base</parameter> parameter, and truncates this result to fit in
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<structname>sd_id128_t</structname> and turns it into a valid Variant 1 Version 4 UUID, in accordance
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with <ulink url="https://tools.ietf.org/html/rfc4122">RFC 4122</ulink>. Neither of the two input
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parameters can be calculated from the output parameter <parameter>ret</parameter>.</para>
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<para><function>sd_id128_get_machine_app_specific()</function> is similar to
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<function>sd_id128_get_machine()</function>, but retrieves a machine ID that is specific to the
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application that is identified by the indicated application ID. It is recommended to use this function
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instead of <function>sd_id128_get_machine()</function> when passing an ID to untrusted environments, in
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order to make sure that the original machine ID may not be determined externally. This way, the ID used
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by the application remains stable on a given machine, but cannot be easily correlated with IDs used in
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other applications on the same machine. The application-specific ID should be generated via a tool like
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<command>systemd-id128 new</command>, and may be compiled into the application. This function will return
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the same application-specific ID for each combination of machine ID and application ID. Internally, this
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function calls <function>sd_id128_get_app_specific()</function> with the result from
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<function>sd_id128_get_machine()</function> and the <parameter>app_id</parameter> parameter.</para>
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<para><function>sd_id128_get_boot()</function> returns the boot ID of the executing kernel. This reads and parses
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the <filename>/proc/sys/kernel/random/boot_id</filename> file exposed by the kernel. It is randomly generated early
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at boot and is unique for every running kernel instance. See <citerefentry
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project='man-pages'><refentrytitle>random</refentrytitle><manvolnum>4</manvolnum></citerefentry> for more
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information. This function also internally caches the returned ID to make this call a cheap operation. It is
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recommended to use this ID as-is only in trusted environments. In untrusted environments it is recommended to
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derive an application specific ID using <function>sd_id128_get_boot_app_specific()</function>, see below.</para>
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<para><function>sd_id128_get_boot_app_specific()</function> is analogous to
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<function>sd_id128_get_machine_app_specific()</function>, but returns an ID that changes between
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boots. Some machines may be used for a long time without rebooting, hence the boot ID may remain constant
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for a long time, and has properties similar to the machine ID during that time.</para>
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<para><function>sd_id128_get_invocation()</function> returns the invocation ID of the currently executed
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service. In its current implementation, this tries to read and parse the following:
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<itemizedlist>
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<listitem>
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<para>The <varname>$INVOCATION_ID</varname> environment variable that the service manager sets when
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activating a service.</para>
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</listitem>
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<listitem>
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<para>An entry in the kernel keyring that the system service manager sets when activating a service.
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</para>
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</listitem>
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</itemizedlist>
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See <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for details. The ID is cached internally. In future a different mechanism to determine the invocation ID
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may be added.</para>
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<para>Note that <function>sd_id128_get_machine_app_specific()</function>,
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<function>sd_id128_get_boot()</function>, <function>sd_id128_get_boot_app_specific()</function>, and
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<function>sd_id128_get_invocation()</function> always return UUID Variant 1 Version 4 compatible IDs.
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<function>sd_id128_get_machine()</function> will also return a UUID Variant 1 Version 4 compatible ID on
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new installations but might not on older. It is possible to convert the machine ID non-reversibly into a
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UUID Variant 1 Version 4 compatible one. For more information, see
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<citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>. It is
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hence guaranteed that these functions will never return the ID consisting of all zero or all one bits
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(<constant>SD_ID128_NULL</constant>, <constant>SD_ID128_ALLF</constant>) — with the possible exception of
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<function>sd_id128_get_machine()</function>, as mentioned.</para>
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<para>For more information about the <literal>sd_id128_t</literal>
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type see
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<citerefentry><refentrytitle>sd-id128</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para>Those calls return 0 on success (in which case <parameter>ret</parameter> is filled in),
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or a negative errno-style error code.</para>
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<refsect2>
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<title>Errors</title>
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<para>Returned errors may indicate the following problems:</para>
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<variablelist>
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<varlistentry>
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<term><constant>-ENOENT</constant></term>
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<listitem><para>Returned by <function>sd_id128_get_machine()</function> and
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<function>sd_id128_get_machine_app_specific()</function> when <filename>/etc/machine-id</filename>
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is missing.</para>
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<xi:include href="version-info.xml" xpointer="v242"/></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ENOMEDIUM</constant></term>
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<listitem><para>Returned by <function>sd_id128_get_machine()</function> and
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<function>sd_id128_get_machine_app_specific()</function> when <filename>/etc/machine-id</filename>
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is empty or all zeros. Also returned by <function>sd_id128_get_invocation()</function> when the
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invocation ID is all zeros.</para>
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<xi:include href="version-info.xml" xpointer="v242"/></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ENOPKG</constant></term>
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<listitem><para>Returned by <function>sd_id128_get_machine()</function> and
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<function>sd_id128_get_machine_app_specific()</function> when the content of
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<filename>/etc/machine-id</filename> is <literal>uninitialized</literal>.</para>
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<xi:include href="version-info.xml" xpointer="v253"/></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ENOSYS</constant></term>
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<listitem><para>Returned by <function>sd_id128_get_boot()</function> and
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<function>sd_id128_get_boot_app_specific()</function> when <filename>/proc/</filename> is not
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mounted.</para>
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<xi:include href="version-info.xml" xpointer="v253"/></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ENXIO</constant></term>
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<listitem><para>Returned by <function>sd_id128_get_invocation()</function> if no invocation ID is
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set. Also returned by <function>sd_id128_get_app_specific()</function>,
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<function>sd_id128_get_machine_app_specific()</function>, and
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<function>sd_id128_get_boot_app_specific()</function> when the <parameter>app_id</parameter>
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parameter is all zeros.</para>
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<xi:include href="version-info.xml" xpointer="v242"/></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-EUCLEAN</constant></term>
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<listitem><para>Returned by any of the functions described here when the configured value has
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invalid format.</para>
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<xi:include href="version-info.xml" xpointer="v253"/></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-EPERM</constant></term>
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<listitem><para>Requested information could not be retrieved because of insufficient permissions.
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</para>
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<xi:include href="version-info.xml" xpointer="v242"/></listitem>
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</varlistentry>
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</variablelist>
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</refsect2>
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</refsect1>
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<xi:include href="libsystemd-pkgconfig.xml" />
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<refsect1>
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<title>Examples</title>
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<example>
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<title>Application-specific machine ID</title>
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<para>First, generate the application ID:</para>
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<programlisting>$ systemd-id128 -p new
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As string:
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c273277323db454ea63bb96e79b53e97
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As UUID:
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c2732773-23db-454e-a63b-b96e79b53e97
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As man:sd-id128(3) macro:
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#define MESSAGE_XYZ SD_ID128_MAKE(c2,73,27,73,23,db,45,4e,a6,3b,b9,6e,79,b5,3e,97)
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...
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</programlisting>
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<para>Then use the new identifier in an example application:</para>
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<programlisting><xi:include href="id128-app-specific.c" parse="text" /></programlisting>
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</example>
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</refsect1>
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<refsect1>
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<title>History</title>
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<para><function>sd_id128_get_machine()</function> and
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<function>sd_id128_get_boot()</function> were added in version 187.</para>
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<para><function>sd_id128_get_invocation()</function> was added in version 232.</para>
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<para><function>sd_id128_get_machine_app_specific()</function> was added in version 233.</para>
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<para><function>sd_id128_get_boot_app_specific()</function> was added in version 240.</para>
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<para><function>sd_id128_get_app_specific()</function> was added in version 255.</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd-id128</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd-id128</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_id128_randomize</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>random</refentrytitle><manvolnum>4</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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