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2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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6 This file is part of systemd.
8 Copyright 2012 Lennart Poettering
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11 under the terms of the GNU Lesser General Public License as published by
12 the Free Software Foundation; either version 2.1 of the License, or
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24 <refentry id="sd_journal_query_unique">
27 <title>sd_journal_query_unique</title>
28 <productname>systemd</productname>
32 <contrib>Developer</contrib>
33 <firstname>Lennart</firstname>
34 <surname>Poettering</surname>
35 <email>lennart@poettering.net</email>
41 <refentrytitle>sd_journal_query_unique</refentrytitle>
42 <manvolnum>3</manvolnum>
46 <refname>sd_journal_query_unique</refname>
47 <refname>sd_journal_enumerate_unique</refname>
48 <refname>sd_journal_restart_unique</refname>
49 <refname>SD_JOURNAL_FOREACH_UNIQUE</refname>
50 <refpurpose>Read unique data fields from the journal</refpurpose>
55 <funcsynopsisinfo>#include <systemd/sd-journal.h></funcsynopsisinfo>
58 <funcdef>int <function>sd_journal_query_unique</function></funcdef>
59 <paramdef>sd_journal* <parameter>j</parameter></paramdef>
60 <paramdef>const char* <parameter>field</parameter></paramdef>
64 <funcdef>int <function>sd_journal_enumerate_unique</function></funcdef>
65 <paramdef>sd_journal* <parameter>j</parameter></paramdef>
66 <paramdef>const void** <parameter>data</parameter></paramdef>
67 <paramdef>size_t* <parameter>length</parameter></paramdef>
71 <funcdef>void <function>sd_journal_restart_unique</function></funcdef>
72 <paramdef>sd_journal* <parameter>j</parameter></paramdef>
76 <funcdef><function>SD_JOURNAL_FOREACH_UNIQUE</function></funcdef>
77 <paramdef>sd_journal* <parameter>j</parameter></paramdef>
78 <paramdef>const void* <parameter>data</parameter></paramdef>
79 <paramdef>size_t <parameter>length</parameter></paramdef>
86 <title>Description</title>
88 <para><function>sd_journal_query_unique()</function>
89 queries the journal for all unique values the
90 specified field can take. It takes two arguments: the
91 journal to query and the field name to look
92 for. Well-known field names are listed on
93 <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>. Field
94 names must be specified without a trailing '='. After
95 this function has been executed successfully the field
96 values may be queried using
97 <function>sd_journal_enumerate_unique()</function>. Invoking
98 this call a second time will change the field name
99 being queried and reset the enumeration index to the
100 first field value that matches.</para>
102 <para><function>sd_journal_enumerate_unique()</function>
103 may be used to iterate through all data fields which
104 match the previously selected field name as set with
105 <function>sd_journal_query_unique()</function>. On
106 each invocation the next field data matching the field
107 name is returned. The order of the returned data
108 fields is not defined. It takes three arguments: the
109 journal context object, plus a pair of pointers to
110 pointer/size variables where the data object and its
111 size shall be stored in. The returned data is in a
112 read-only memory map and is only valid until the next
114 <function>sd_journal_enumerate_unique()</function>. Note
115 that the data returned will be prefixed with the field
118 <para><function>sd_journal_restart_unique()</function>
119 resets the data enumeration index to the beginning of
120 the list. The next invocation of
121 <function>sd_journal_enumerate_unique()</function>
122 will return the first field data matching the field
126 <function>SD_JOURNAL_FOREACH_UNIQUE()</function> macro
127 may be used as a handy wrapper around
128 <function>sd_journal_restart_unique()</function> and
129 <function>sd_journal_enumerate_unique()</function>.</para>
131 <para>Note that these functions currently are not
132 influenced by matches set with
133 <function>sd_journal_add_match()</function> but this
134 might change in a later version of this
139 <title>Return Value</title>
141 <para><function>sd_journal_query_unique()</function>
142 returns 0 on success or a negative errno-style error
143 code. <function>sd_journal_enumerate_unique()</function>
144 returns a positive integer if the next field data has
145 been read, 0 when no more fields are known, or a
146 negative errno-style error
147 code. <function>sd_journal_restart_unique()</function>
148 returns nothing.</para>
154 <para>The <function>sd_journal_query_unique()</function>,
155 <function>sd_journal_enumerate_unique()</function> and
156 <function>sd_journal_restart_unique()</function>
157 interfaces are available as shared library, which can
158 be compiled and linked to with the
159 <literal>libsystemd-journal</literal>
160 <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
165 <title>Examples</title>
168 <function>SD_JOURNAL_FOREACH_UNIQUE</function> macro
169 to iterate through all values a field of the journal
170 can take. The following example lists all unit names
171 referenced in the journal:</para>
173 <programlisting>#include <stdio.h>
174 #include <string.h>
175 #include <systemd/sd-journal.h>
177 int main(int argc, char *argv[]) {
183 r = sd_journal_open(&j, SD_JOURNAL_LOCAL_ONLY);
185 fprintf(stderr, "Failed to open journal: %s\n", strerror(-r));
188 r = sd_journal_query_unique(j, "_SYSTEMD_UNIT");
190 fprintf(stderr, "Failed to query journal: %s\n", strerror(-r));
193 SD_JOURNAL_FOREACH_UNIQUE(j, d, l)
194 printf("%.*s\n", (int) l, (const char*) d);
202 <title>See Also</title>
205 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
206 <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
207 <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
208 <citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
209 <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
210 <citerefentry><refentrytitle>sd_journal_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry>