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a4023a43 | 1 | <?xml version='1.0'?> <!--*-nxml-*--> |
3a54a157 | 2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" |
12b42c76 | 3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> |
0307f791 | 4 | <!-- SPDX-License-Identifier: LGPL-2.1+ --> |
a4023a43 | 5 | |
7d6b2723 | 6 | <refentry id="sd_id128_get_machine" xmlns:xi="http://www.w3.org/2001/XInclude"> |
a4023a43 | 7 | |
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8 | <refentryinfo> |
9 | <title>sd_id128_get_machine</title> | |
10 | <productname>systemd</productname> | |
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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> | |
70fc4f57 | 20 | <refname>sd_id128_get_machine_app_specific</refname> |
798d3a52 | 21 | <refname>sd_id128_get_boot</refname> |
65d410c7 | 22 | <refname>sd_id128_get_boot_app_specific</refname> |
4b58153d | 23 | <refname>sd_id128_get_invocation</refname> |
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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 | ||
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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 | ||
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42 | <funcprototype> |
43 | <funcdef>int <function>sd_id128_get_boot</function></funcdef> | |
44 | <paramdef>sd_id128_t *<parameter>ret</parameter></paramdef> | |
45 | </funcprototype> | |
46 | ||
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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 | ||
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53 | <funcprototype> |
54 | <funcdef>int <function>sd_id128_get_invocation</function></funcdef> | |
55 | <paramdef>sd_id128_t *<parameter>ret</parameter></paramdef> | |
56 | </funcprototype> | |
57 | ||
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58 | </funcsynopsis> |
59 | </refsynopsisdiv> | |
60 | ||
61 | <refsect1> | |
62 | <title>Description</title> | |
63 | ||
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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 irreversable (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 | |
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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 | |
0d1d512f | 78 | machine. The application-specific ID should be generated via a tool like <command>systemd-id128 new</command>, |
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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> | |
798d3a52 | 95 | |
4b58153d LP |
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 | ||
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102 | <para>Note that <function>sd_id128_get_machine_app_specific()</function>, <function>sd_id128_get_boot()</function>, |
103 | <function>sd_id128_get_boot_app_specific()</function>, and <function>sd_id128_get_invocation()</function> always | |
104 | return UUID v4 compatible IDs. <function>sd_id128_get_machine()</function> will also return a UUID v4-compatible | |
105 | ID on new installations but might not on older. It is possible to convert the machine ID into a UUID v4-compatible | |
106 | one. For more information, see | |
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107 | <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para> |
108 | ||
109 | <para>For more information about the <literal>sd_id128_t</literal> | |
110 | type see | |
111 | <citerefentry><refentrytitle>sd-id128</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para> | |
112 | </refsect1> | |
113 | ||
114 | <refsect1> | |
115 | <title>Return Value</title> | |
116 | ||
ea03f6ba | 117 | <para>Those calls return 0 on success (in which case <parameter>ret</parameter> is filled in), |
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118 | or a negative errno-style error code. In particular, |
119 | <function>sd_id128_get_machine()</function>, | |
120 | <function>sd_id128_get_machine_app_specific()</function>, and | |
121 | <function>sd_id128_get_boot_app_specific()</function> return <constant>-ENOENT</constant> if | |
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122 | <filename>/etc/machine-id</filename> is missing, and <constant>-ENOMEDIUM</constant> if |
123 | <filename>/etc/machine-id</filename> is empty or all zeros.</para> | |
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124 | </refsect1> |
125 | ||
7d6b2723 | 126 | <xi:include href="libsystemd-pkgconfig.xml" /> |
798d3a52 | 127 | |
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128 | <refsect1> |
129 | <title>Examples</title> | |
130 | ||
131 | <example> | |
132 | <title>Application-specific machine ID</title> | |
133 | ||
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134 | <para>First, generate the application ID:</para> |
135 | <programlisting>$ systemd-id128 -p new | |
136 | As string: | |
137 | c273277323db454ea63bb96e79b53e97 | |
138 | ||
139 | As UUID: | |
140 | c2732773-23db-454e-a63b-b96e79b53e97 | |
141 | ||
142 | As man:sd-id128(3) macro: | |
143 | #define MESSAGE_XYZ SD_ID128_MAKE(c2,73,27,73,23,db,45,4e,a6,3b,b9,6e,79,b5,3e,97) | |
144 | ... | |
145 | </programlisting> | |
146 | ||
147 | <para>Then use the new identifier in an example application:</para> | |
70fc4f57 | 148 | |
787f78b6 | 149 | <programlisting><xi:include href="id128-app-specific.c" parse="text" /></programlisting> |
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150 | </example> |
151 | </refsect1> | |
152 | ||
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153 | <refsect1> |
154 | <title>See Also</title> | |
155 | ||
156 | <para> | |
157 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
0d1d512f | 158 | <citerefentry><refentrytitle>systemd-id128</refentrytitle><manvolnum>1</manvolnum></citerefentry>, |
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159 | <citerefentry><refentrytitle>sd-id128</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
160 | <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>, | |
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161 | <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>, |
162 | <citerefentry><refentrytitle>sd_id128_randomize</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
163 | <citerefentry project='man-pages'><refentrytitle>random</refentrytitle><manvolnum>4</manvolnum></citerefentry> | |
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164 | </para> |
165 | </refsect1> | |
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166 | |
167 | </refentry> |