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1 | <?xml version='1.0'?> <!--*-nxml-*--> |
2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" | |
12b42c76 | 3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> |
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4 | |
5 | <!-- | |
572eb058 | 6 | SPDX-License-Identifier: LGPL-2.1+ |
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7 | --> |
8 | ||
7d6b2723 | 9 | <refentry id="sd_id128_get_machine" xmlns:xi="http://www.w3.org/2001/XInclude"> |
a4023a43 | 10 | |
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11 | <refentryinfo> |
12 | <title>sd_id128_get_machine</title> | |
13 | <productname>systemd</productname> | |
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14 | </refentryinfo> |
15 | ||
16 | <refmeta> | |
17 | <refentrytitle>sd_id128_get_machine</refentrytitle> | |
18 | <manvolnum>3</manvolnum> | |
19 | </refmeta> | |
20 | ||
21 | <refnamediv> | |
22 | <refname>sd_id128_get_machine</refname> | |
70fc4f57 | 23 | <refname>sd_id128_get_machine_app_specific</refname> |
798d3a52 | 24 | <refname>sd_id128_get_boot</refname> |
65d410c7 | 25 | <refname>sd_id128_get_boot_app_specific</refname> |
4b58153d | 26 | <refname>sd_id128_get_invocation</refname> |
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27 | <refpurpose>Retrieve 128-bit IDs</refpurpose> |
28 | </refnamediv> | |
29 | ||
30 | <refsynopsisdiv> | |
31 | <funcsynopsis> | |
32 | <funcsynopsisinfo>#include <systemd/sd-id128.h></funcsynopsisinfo> | |
33 | ||
34 | <funcprototype> | |
35 | <funcdef>int <function>sd_id128_get_machine</function></funcdef> | |
36 | <paramdef>sd_id128_t *<parameter>ret</parameter></paramdef> | |
37 | </funcprototype> | |
38 | ||
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39 | <funcprototype> |
40 | <funcdef>int <function>sd_id128_get_machine_app_specific</function></funcdef> | |
41 | <paramdef>sd_id128_t <parameter>app_id</parameter></paramdef> | |
42 | <paramdef>sd_id128_t *<parameter>ret</parameter></paramdef> | |
43 | </funcprototype> | |
44 | ||
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45 | <funcprototype> |
46 | <funcdef>int <function>sd_id128_get_boot</function></funcdef> | |
47 | <paramdef>sd_id128_t *<parameter>ret</parameter></paramdef> | |
48 | </funcprototype> | |
49 | ||
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50 | <funcprototype> |
51 | <funcdef>int <function>sd_id128_get_boot_app_specific</function></funcdef> | |
52 | <paramdef>sd_id128_t <parameter>app_id</parameter></paramdef> | |
53 | <paramdef>sd_id128_t *<parameter>ret</parameter></paramdef> | |
54 | </funcprototype> | |
55 | ||
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56 | <funcprototype> |
57 | <funcdef>int <function>sd_id128_get_invocation</function></funcdef> | |
58 | <paramdef>sd_id128_t *<parameter>ret</parameter></paramdef> | |
59 | </funcprototype> | |
60 | ||
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61 | </funcsynopsis> |
62 | </refsynopsisdiv> | |
63 | ||
64 | <refsect1> | |
65 | <title>Description</title> | |
66 | ||
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67 | <para><function>sd_id128_get_machine()</function> returns the machine ID of the executing host. This reads and |
68 | parses the <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry> | |
69 | file. This function caches the machine ID internally to make retrieving the machine ID a cheap operation. This ID | |
70 | may be used wherever a unique identifier for the local system is needed. However, it is recommended to use this ID | |
71 | as-is only in trusted environments. In untrusted environments it is recommended to derive an application specific | |
72 | ID from this machine ID, in an irreversable (cryptographically secure) way. To make this easy | |
73 | <function>sd_id128_get_machine_app_specific()</function> is provided, see below.</para> | |
74 | ||
75 | <para><function>sd_id128_get_machine_app_specific()</function> is similar to | |
76 | <function>sd_id128_get_machine()</function>, but retrieves a machine ID that is specific to the application that is | |
77 | identified by the indicated application ID. It is recommended to use this function instead of | |
78 | <function>sd_id128_get_machine()</function> when passing an ID to untrusted environments, in order to make sure | |
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79 | that the original machine ID may not be determined externally. This way, the ID used by the application remains |
80 | stable on a given machine, but cannot be easily correlated with IDs used in other applications on the same | |
0d1d512f | 81 | machine. The application-specific ID should be generated via a tool like <command>systemd-id128 new</command>, |
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82 | and may be compiled into the application. This function will return the same application-specific ID for each |
83 | combination of machine ID and application ID. Internally, this function calculates HMAC-SHA256 of the application | |
84 | ID, keyed by the machine ID.</para> | |
85 | ||
86 | <para><function>sd_id128_get_boot()</function> returns the boot ID of the executing kernel. This reads and parses | |
87 | the <filename>/proc/sys/kernel/random/boot_id</filename> file exposed by the kernel. It is randomly generated early | |
88 | at boot and is unique for every running kernel instance. See <citerefentry | |
89 | project='man-pages'><refentrytitle>random</refentrytitle><manvolnum>4</manvolnum></citerefentry> for more | |
90 | information. This function also internally caches the returned ID to make this call a cheap operation. It is | |
91 | recommended to use this ID as-is only in trusted environments. In untrusted environments it is recommended to | |
92 | derive an application specific ID using <function>sd_id128_get_machine_app_specific()</function>, see below.</para> | |
93 | ||
94 | <para><function>sd_id128_get_boot_app_specific()</function> is analogous to | |
95 | <function>sd_id128_get_machine_app_specific()</function> but returns an ID that changes between boots. Some | |
96 | machines may be used for a long time without rebooting, hence the boot ID may remain constant for a long time, and | |
97 | has properties similar to the machine ID during that time.</para> | |
798d3a52 | 98 | |
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99 | <para><function>sd_id128_get_invocation()</function> returns the invocation ID of the currently executed |
100 | service. In its current implementation, this reads and parses the <varname>$INVOCATION_ID</varname> environment | |
101 | variable that the service manager sets when activating a service, see | |
102 | <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for details. The | |
103 | ID is cached internally. In future a different mechanism to determine the invocation ID may be added.</para> | |
104 | ||
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105 | <para>Note that <function>sd_id128_get_machine_app_specific()</function>, <function>sd_id128_get_boot()</function>, |
106 | <function>sd_id128_get_boot_app_specific()</function>, and <function>sd_id128_get_invocation()</function> always | |
107 | return UUID v4 compatible IDs. <function>sd_id128_get_machine()</function> will also return a UUID v4-compatible | |
108 | ID on new installations but might not on older. It is possible to convert the machine ID into a UUID v4-compatible | |
109 | one. For more information, see | |
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110 | <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para> |
111 | ||
112 | <para>For more information about the <literal>sd_id128_t</literal> | |
113 | type see | |
114 | <citerefentry><refentrytitle>sd-id128</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para> | |
115 | </refsect1> | |
116 | ||
117 | <refsect1> | |
118 | <title>Return Value</title> | |
119 | ||
ea03f6ba | 120 | <para>Those calls return 0 on success (in which case <parameter>ret</parameter> is filled in), |
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121 | or a negative errno-style error code. In particular, |
122 | <function>sd_id128_get_machine()</function>, | |
123 | <function>sd_id128_get_machine_app_specific()</function>, and | |
124 | <function>sd_id128_get_boot_app_specific()</function> return <constant>-ENOENT</constant> if | |
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125 | <filename>/etc/machine-id</filename> is missing, and <constant>-ENOMEDIUM</constant> if |
126 | <filename>/etc/machine-id</filename> is empty or all zeros.</para> | |
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127 | </refsect1> |
128 | ||
7d6b2723 | 129 | <xi:include href="libsystemd-pkgconfig.xml" /> |
798d3a52 | 130 | |
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131 | <refsect1> |
132 | <title>Examples</title> | |
133 | ||
134 | <example> | |
135 | <title>Application-specific machine ID</title> | |
136 | ||
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137 | <para>First, generate the application ID:</para> |
138 | <programlisting>$ systemd-id128 -p new | |
139 | As string: | |
140 | c273277323db454ea63bb96e79b53e97 | |
141 | ||
142 | As UUID: | |
143 | c2732773-23db-454e-a63b-b96e79b53e97 | |
144 | ||
145 | As man:sd-id128(3) macro: | |
146 | #define MESSAGE_XYZ SD_ID128_MAKE(c2,73,27,73,23,db,45,4e,a6,3b,b9,6e,79,b5,3e,97) | |
147 | ... | |
148 | </programlisting> | |
149 | ||
150 | <para>Then use the new identifier in an example application:</para> | |
70fc4f57 | 151 | |
787f78b6 | 152 | <programlisting><xi:include href="id128-app-specific.c" parse="text" /></programlisting> |
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153 | </example> |
154 | </refsect1> | |
155 | ||
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156 | <refsect1> |
157 | <title>See Also</title> | |
158 | ||
159 | <para> | |
160 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
0d1d512f | 161 | <citerefentry><refentrytitle>systemd-id128</refentrytitle><manvolnum>1</manvolnum></citerefentry>, |
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162 | <citerefentry><refentrytitle>sd-id128</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
163 | <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>, | |
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164 | <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>, |
165 | <citerefentry><refentrytitle>sd_id128_randomize</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
166 | <citerefentry project='man-pages'><refentrytitle>random</refentrytitle><manvolnum>4</manvolnum></citerefentry> | |
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167 | </para> |
168 | </refsect1> | |
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169 | |
170 | </refentry> |