1<?xml version='1.0'?> <!--*-nxml-*--> 2<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" 3 "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> 4<!-- SPDX-License-Identifier: LGPL-2.1-or-later --> 5 6<refentry id="sd_id128_get_machine" xmlns:xi="http://www.w3.org/2001/XInclude"> 7 8 <refentryinfo> 9 <title>sd_id128_get_machine</title> 10 <productname>systemd</productname> 11 </refentryinfo> 12 13 <refmeta> 14 <refentrytitle>sd_id128_get_machine</refentrytitle> 15 <manvolnum>3</manvolnum> 16 </refmeta> 17 18 <refnamediv> 19 <refname>sd_id128_get_machine</refname> 20 <refname>sd_id128_get_machine_app_specific</refname> 21 <refname>sd_id128_get_boot</refname> 22 <refname>sd_id128_get_boot_app_specific</refname> 23 <refname>sd_id128_get_invocation</refname> 24 <refpurpose>Retrieve 128-bit IDs</refpurpose> 25 </refnamediv> 26 27 <refsynopsisdiv> 28 <funcsynopsis> 29 <funcsynopsisinfo>#include <systemd/sd-id128.h></funcsynopsisinfo> 30 31 <funcprototype> 32 <funcdef>int <function>sd_id128_get_machine</function></funcdef> 33 <paramdef>sd_id128_t *<parameter>ret</parameter></paramdef> 34 </funcprototype> 35 36 <funcprototype> 37 <funcdef>int <function>sd_id128_get_machine_app_specific</function></funcdef> 38 <paramdef>sd_id128_t <parameter>app_id</parameter></paramdef> 39 <paramdef>sd_id128_t *<parameter>ret</parameter></paramdef> 40 </funcprototype> 41 42 <funcprototype> 43 <funcdef>int <function>sd_id128_get_boot</function></funcdef> 44 <paramdef>sd_id128_t *<parameter>ret</parameter></paramdef> 45 </funcprototype> 46 47 <funcprototype> 48 <funcdef>int <function>sd_id128_get_boot_app_specific</function></funcdef> 49 <paramdef>sd_id128_t <parameter>app_id</parameter></paramdef> 50 <paramdef>sd_id128_t *<parameter>ret</parameter></paramdef> 51 </funcprototype> 52 53 <funcprototype> 54 <funcdef>int <function>sd_id128_get_invocation</function></funcdef> 55 <paramdef>sd_id128_t *<parameter>ret</parameter></paramdef> 56 </funcprototype> 57 58 </funcsynopsis> 59 </refsynopsisdiv> 60 61 <refsect1> 62 <title>Description</title> 63 64 <para><function>sd_id128_get_machine()</function> returns the machine ID of the executing host. This reads and 65 parses the <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry> 66 file. This function caches the machine ID internally to make retrieving the machine ID a cheap operation. This ID 67 may be used wherever a unique identifier for the local system is needed. However, it is recommended to use this ID 68 as-is only in trusted environments. In untrusted environments it is recommended to derive an application specific 69 ID from this machine ID, in an irreversible (cryptographically secure) way. To make this easy 70 <function>sd_id128_get_machine_app_specific()</function> is provided, see below.</para> 71 72 <para><function>sd_id128_get_machine_app_specific()</function> is similar to 73 <function>sd_id128_get_machine()</function>, but retrieves a machine ID that is specific to the application that is 74 identified by the indicated application ID. It is recommended to use this function instead of 75 <function>sd_id128_get_machine()</function> when passing an ID to untrusted environments, in order to make sure 76 that the original machine ID may not be determined externally. This way, the ID used by the application remains 77 stable on a given machine, but cannot be easily correlated with IDs used in other applications on the same 78 machine. The application-specific ID should be generated via a tool like <command>systemd-id128 new</command>, 79 and may be compiled into the application. This function will return the same application-specific ID for each 80 combination of machine ID and application ID. Internally, this function calculates HMAC-SHA256 of the application 81 ID, keyed by the machine ID.</para> 82 83 <para><function>sd_id128_get_boot()</function> returns the boot ID of the executing kernel. This reads and parses 84 the <filename>/proc/sys/kernel/random/boot_id</filename> file exposed by the kernel. It is randomly generated early 85 at boot and is unique for every running kernel instance. See <citerefentry 86 project='man-pages'><refentrytitle>random</refentrytitle><manvolnum>4</manvolnum></citerefentry> for more 87 information. This function also internally caches the returned ID to make this call a cheap operation. It is 88 recommended to use this ID as-is only in trusted environments. In untrusted environments it is recommended to 89 derive an application specific ID using <function>sd_id128_get_machine_app_specific()</function>, see below.</para> 90 91 <para><function>sd_id128_get_boot_app_specific()</function> is analogous to 92 <function>sd_id128_get_machine_app_specific()</function> but returns an ID that changes between boots. Some 93 machines may be used for a long time without rebooting, hence the boot ID may remain constant for a long time, and 94 has properties similar to the machine ID during that time.</para> 95 96 <para><function>sd_id128_get_invocation()</function> returns the invocation ID of the currently executed 97 service. In its current implementation, this reads and parses the <varname>$INVOCATION_ID</varname> environment 98 variable that the service manager sets when activating a service, see 99 <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for details. The 100 ID is cached internally. In future a different mechanism to determine the invocation ID may be added.</para> 101 102 <para>Note that <function>sd_id128_get_machine_app_specific()</function>, 103 <function>sd_id128_get_boot()</function>, <function>sd_id128_get_boot_app_specific()</function>, and 104 <function>sd_id128_get_invocation()</function> always return UUID Variant 1 Version 4 compatible IDs. 105 <function>sd_id128_get_machine()</function> will also return a UUID Variant 1 Version 4 compatible ID on 106 new installations but might not on older. It is possible to convert the machine ID non-reversibly into a 107 UUID Variant 1 Version 4 compatible one. For more information, see 108 <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>. It is 109 hence guaranteed that these functions will never return the ID consisting of all zero or all one bits 110 (<constant>SD_ID128_NULL</constant>, <constant>SD_ID128_ALLF</constant>) — with the possible exception of 111 <function>sd_id128_get_machine()</function>, as mentioned.</para> 112 113 <para>For more information about the <literal>sd_id128_t</literal> 114 type see 115 <citerefentry><refentrytitle>sd-id128</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para> 116 </refsect1> 117 118 <refsect1> 119 <title>Return Value</title> 120 121 <para>Those calls return 0 on success (in which case <parameter>ret</parameter> is filled in), 122 or a negative errno-style error code.</para> 123 124 <refsect2> 125 <title>Errors</title> 126 <para>Returned errors may indicate the following problems:</para> 127 128 <variablelist> 129 <varlistentry> 130 <term><constant>-ENOENT</constant></term> 131 132 <listitem><para>Returned by <function>sd_id128_get_machine()</function>, 133 <function>sd_id128_get_machine_app_specific()</function>, and 134 <function>sd_id128_get_boot_app_specific()</function> when <filename>/etc/machine-id</filename> is 135 missing.</para></listitem> 136 </varlistentry> 137 138 <varlistentry> 139 <term><constant>-ENOMEDIUM</constant></term> 140 141 <listitem><para>Returned by <function>sd_id128_get_machine()</function>, 142 <function>sd_id128_get_machine_app_specific()</function>, and 143 <function>sd_id128_get_boot_app_specific()</function> when <filename>/etc/machine-id</filename> is 144 empty or all zeros.</para></listitem> 145 </varlistentry> 146 147 <varlistentry> 148 <term><constant>-ENXIO</constant></term> 149 150 <listitem><para>Returned by <function>sd_id128_get_invocation()</function> if no invocation ID is 151 set.</para></listitem> 152 </varlistentry> 153 154 <varlistentry> 155 <term><constant>-EIO</constant></term> 156 157 <listitem><para>Returned by any of the functions described here when the configured value has 158 invalid format.</para></listitem> 159 </varlistentry> 160 161 <varlistentry> 162 <term><constant>-EPERM</constant></term> 163 164 <listitem><para>Requested information could not be retrieved because of insufficient permissions. 165 </para></listitem> 166 </varlistentry> 167 </variablelist> 168 </refsect2> 169 </refsect1> 170 171 <xi:include href="libsystemd-pkgconfig.xml" /> 172 173 <refsect1> 174 <title>Examples</title> 175 176 <example> 177 <title>Application-specific machine ID</title> 178 179 <para>First, generate the application ID:</para> 180 <programlisting>$ systemd-id128 -p new 181As string: 182c273277323db454ea63bb96e79b53e97 183 184As UUID: 185c2732773-23db-454e-a63b-b96e79b53e97 186 187As man:sd-id128(3) macro: 188#define MESSAGE_XYZ SD_ID128_MAKE(c2,73,27,73,23,db,45,4e,a6,3b,b9,6e,79,b5,3e,97) 189... 190</programlisting> 191 192 <para>Then use the new identifier in an example application:</para> 193 194 <programlisting><xi:include href="id128-app-specific.c" parse="text" /></programlisting> 195 </example> 196 </refsect1> 197 198 <refsect1> 199 <title>See Also</title> 200 201 <para> 202 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, 203 <citerefentry><refentrytitle>systemd-id128</refentrytitle><manvolnum>1</manvolnum></citerefentry>, 204 <citerefentry><refentrytitle>sd-id128</refentrytitle><manvolnum>3</manvolnum></citerefentry>, 205 <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>, 206 <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>, 207 <citerefentry><refentrytitle>sd_id128_randomize</refentrytitle><manvolnum>3</manvolnum></citerefentry>, 208 <citerefentry project='man-pages'><refentrytitle>random</refentrytitle><manvolnum>4</manvolnum></citerefentry> 209 </para> 210 </refsect1> 211 212</refentry> 213