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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> | |
14 | ||
15 | <authorgroup> | |
16 | <author> | |
17 | <contrib>Developer</contrib> | |
18 | <firstname>Lennart</firstname> | |
19 | <surname>Poettering</surname> | |
20 | <email>lennart@poettering.net</email> | |
21 | </author> | |
22 | </authorgroup> | |
23 | </refentryinfo> | |
24 | ||
25 | <refmeta> | |
26 | <refentrytitle>sd_id128_get_machine</refentrytitle> | |
27 | <manvolnum>3</manvolnum> | |
28 | </refmeta> | |
29 | ||
30 | <refnamediv> | |
31 | <refname>sd_id128_get_machine</refname> | |
70fc4f57 | 32 | <refname>sd_id128_get_machine_app_specific</refname> |
798d3a52 | 33 | <refname>sd_id128_get_boot</refname> |
4b58153d | 34 | <refname>sd_id128_get_invocation</refname> |
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35 | <refpurpose>Retrieve 128-bit IDs</refpurpose> |
36 | </refnamediv> | |
37 | ||
38 | <refsynopsisdiv> | |
39 | <funcsynopsis> | |
40 | <funcsynopsisinfo>#include <systemd/sd-id128.h></funcsynopsisinfo> | |
41 | ||
42 | <funcprototype> | |
43 | <funcdef>int <function>sd_id128_get_machine</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_machine_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_boot</function></funcdef> | |
55 | <paramdef>sd_id128_t *<parameter>ret</parameter></paramdef> | |
56 | </funcprototype> | |
57 | ||
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58 | <funcprototype> |
59 | <funcdef>int <function>sd_id128_get_invocation</function></funcdef> | |
60 | <paramdef>sd_id128_t *<parameter>ret</parameter></paramdef> | |
61 | </funcprototype> | |
62 | ||
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63 | </funcsynopsis> |
64 | </refsynopsisdiv> | |
65 | ||
66 | <refsect1> | |
67 | <title>Description</title> | |
68 | ||
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69 | <para><function>sd_id128_get_machine()</function> returns the machine ID of the executing host. This reads and |
70 | parses the <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry> | |
71 | file. This function caches the machine ID internally to make retrieving the machine ID a cheap operation. This ID | |
72 | may be used wherever a unique identifier for the local system is needed. However, it is recommended to use this ID | |
73 | as-is only in trusted environments. In untrusted environments it is recommended to derive an application specific | |
74 | ID from this machine ID, in an irreversable (cryptographically secure) way. To make this easy | |
75 | <function>sd_id128_get_machine_app_specific()</function> is provided, see below.</para> | |
76 | ||
77 | <para><function>sd_id128_get_machine_app_specific()</function> is similar to | |
78 | <function>sd_id128_get_machine()</function>, but retrieves a machine ID that is specific to the application that is | |
79 | identified by the indicated application ID. It is recommended to use this function instead of | |
80 | <function>sd_id128_get_machine()</function> when passing an ID to untrusted environments, in order to make sure | |
81 | that the original machine ID may not be determined externally. The application-specific ID should be generated via | |
82 | a tool like <command>journalctl --new-id128</command>, and may be compiled into the application. This function will | |
83 | return the same application-specific ID for each combination of machine ID and application ID. Internally, this | |
84 | function calculates HMAC-SHA256 of the application ID, keyed by the machine ID.</para> | |
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85 | |
86 | <para><function>sd_id128_get_boot()</function> returns the boot ID | |
87 | of the executing kernel. This reads and parses the | |
88 | <filename>/proc/sys/kernel/random/boot_id</filename> file exposed | |
89 | by the kernel. It is randomly generated early at boot and is | |
90 | unique for every running kernel instance. See | |
91 | <citerefentry project='man-pages'><refentrytitle>random</refentrytitle><manvolnum>4</manvolnum></citerefentry> | |
92 | for more information. This function also internally caches the | |
93 | returned ID to make this call a cheap operation.</para> | |
94 | ||
4b58153d LP |
95 | <para><function>sd_id128_get_invocation()</function> returns the invocation ID of the currently executed |
96 | service. In its current implementation, this reads and parses the <varname>$INVOCATION_ID</varname> environment | |
97 | variable that the service manager sets when activating a service, see | |
98 | <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for details. The | |
99 | ID is cached internally. In future a different mechanism to determine the invocation ID may be added.</para> | |
100 | ||
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101 | <para>Note that <function>sd_id128_get_machine_app_specific()</function>, <function>sd_id128_get_boot()</function> |
102 | and <function>sd_id128_get_invocation()</function> always return UUID v4 compatible IDs. | |
103 | <function>sd_id128_get_machine()</function> will also return a UUID v4-compatible ID on new installations but might | |
104 | not on older. It is possible to convert the machine ID into a UUID v4-compatible one. For more information, see | |
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105 | <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para> |
106 | ||
107 | <para>For more information about the <literal>sd_id128_t</literal> | |
108 | type see | |
109 | <citerefentry><refentrytitle>sd-id128</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para> | |
110 | </refsect1> | |
111 | ||
112 | <refsect1> | |
113 | <title>Return Value</title> | |
114 | ||
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115 | <para>Those calls return 0 on success (in which case <parameter>ret</parameter> is filled in), |
116 | or a negative errno-style error code. In particular, <function>sd_id128_get_machine()</function> | |
117 | and <function>sd_id128_get_machine_app_specific()</function> return <constant>-ENOENT</constant> | |
118 | if <filename>/etc/machine-id</filename> is missing, and <constant>-ENOMEDIUM</constant> if is | |
119 | empty or all zeros.</para> | |
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120 | </refsect1> |
121 | ||
7d6b2723 | 122 | <xi:include href="libsystemd-pkgconfig.xml" /> |
798d3a52 | 123 | |
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124 | <refsect1> |
125 | <title>Examples</title> | |
126 | ||
127 | <example> | |
128 | <title>Application-specific machine ID</title> | |
129 | ||
130 | <para>Here's a simple example for an application specific machine ID:</para> | |
131 | ||
132 | <programlisting>#include <systemd/sd-id128.h> | |
133 | #include <stdio.h> | |
134 | ||
135 | #define OUR_APPLICATION_ID SD_ID128_MAKE(c2,73,27,73,23,db,45,4e,a6,3b,b9,6e,79,b5,3e,97) | |
136 | ||
137 | int main(int argc, char *argv[]) { | |
138 | sd_id128_t id; | |
139 | sd_id128_get_machine_app_specific(OUR_APPLICATION_ID, &id); | |
140 | printf("Our application ID: " SD_ID128_FORMAT_STR "\n", SD_ID128_FORMAT_VAL(id)); | |
141 | return 0; | |
142 | }</programlisting> | |
143 | </example> | |
144 | </refsect1> | |
145 | ||
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146 | <refsect1> |
147 | <title>See Also</title> | |
148 | ||
149 | <para> | |
150 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
151 | <citerefentry><refentrytitle>sd-id128</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
152 | <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>, | |
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153 | <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>, |
154 | <citerefentry><refentrytitle>sd_id128_randomize</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
155 | <citerefentry project='man-pages'><refentrytitle>random</refentrytitle><manvolnum>4</manvolnum></citerefentry> | |
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156 | </para> |
157 | </refsect1> | |
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158 | |
159 | </refentry> |