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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
10 systemd is free software; you can redistribute it and/or modify it
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_open">
27 <title>sd_journal_open</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_open</refentrytitle>
42 <manvolnum>3</manvolnum>
46 <refname>sd_journal_open</refname>
47 <refname>sd_journal_open_directory</refname>
48 <refname>sd_journal_open_files</refname>
49 <refname>sd_journal_close</refname>
50 <refname>sd_journal</refname>
51 <refname>SD_JOURNAL_LOCAL_ONLY</refname>
52 <refname>SD_JOURNAL_RUNTIME_ONLY</refname>
53 <refname>SD_JOURNAL_SYSTEM</refname>
54 <refname>SD_JOURNAL_CURRENT_USER</refname>
55 <refpurpose>Open the system journal for reading</refpurpose>
60 <funcsynopsisinfo>#include <systemd/sd-journal.h></funcsynopsisinfo>
63 <funcdef>int <function>sd_journal_open</function></funcdef>
64 <paramdef>sd_journal** <parameter>ret</parameter></paramdef>
65 <paramdef>int <parameter>flags</parameter></paramdef>
69 <funcdef>int <function>sd_journal_open_directory</function></funcdef>
70 <paramdef>sd_journal** <parameter>ret</parameter></paramdef>
71 <paramdef>const char* <parameter>path</parameter></paramdef>
72 <paramdef>int <parameter>flags</parameter></paramdef>
76 <funcdef>int <function>sd_journal_open_files</function></funcdef>
77 <paramdef>sd_journal** <parameter>ret</parameter></paramdef>
78 <paramdef>const char** <parameter>paths</parameter></paramdef>
79 <paramdef>int <parameter>flags</parameter></paramdef>
83 <funcdef>void <function>sd_journal_close</function></funcdef>
84 <paramdef>sd_journal* <parameter>j</parameter></paramdef>
90 <title>Description</title>
92 <para><function>sd_journal_open()</function> opens
93 the log journal for reading. It will find all journal
94 files automatically and interleave them automatically
95 when reading. As first argument it takes a pointer to
96 a <varname>sd_journal</varname> pointer, which on
97 success will contain a journal context object. The
98 second argument is a flags field, which may consist of
99 the following flags ORed together:
100 <constant>SD_JOURNAL_LOCAL_ONLY</constant> makes sure
101 only journal files generated on the local machine will
102 be opened. <constant>SD_JOURNAL_RUNTIME_ONLY</constant>
103 makes sure only volatile journal files will be opened,
104 excluding those which are stored on persistent
105 storage. <constant>SD_JOURNAL_SYSTEM</constant>
106 will cause journal files of system services and the
107 kernel (in opposition to user session processes) to
108 be opened. <constant>SD_JOURNAL_CURRENT_USER</constant>
109 will cause journal files of the current user to be
110 opened. If neither <constant>SD_JOURNAL_SYSTEM</constant>
111 nor <constant>SD_JOURNAL_CURRENT_USER</constant> are
112 specified, all journal file types will be opened.</para>
114 <para><function>sd_journal_open_directory()</function>
115 is similar to <function>sd_journal_open()</function>
116 but takes an absolute directory path as argument. All
117 journal files in this directory will be opened and
118 interleaved automatically. This call also takes a
119 flags argument, but it must be passed as 0 as no flags
120 are currently understood for this call.</para>
122 <para><function>sd_journal_open_files()</function>
123 is similar to <function>sd_journal_open()</function>
124 but takes a <constant>NULL</constant>-terminated list
125 of file paths to open. All files will be opened and
126 interleaved automatically. This call also takes a
127 flags argument, but it must be passed as 0 as no flags
128 are currently understood for this call. Please note
129 that in the case of a live journal, this function is only
130 useful for debugging, because individual journal files
131 can be rotated at any moment, and the opening of
132 specific files is inherently racy.</para>
134 <para><varname>sd_journal</varname> objects cannot be
135 used in the child after a fork. Functions which take a
136 journal object as an argument
137 (<function>sd_journal_next()</function> and others)
138 will return <constant>-ECHILD</constant> after a fork.
141 <para><function>sd_journal_close()</function> will
142 close the journal context allocated with
143 <function>sd_journal_open()</function> or
144 <function>sd_journal_open_directory()</function> and
145 free its resources.</para>
147 <para>When opening the journal only journal files
148 accessible to the calling user will be opened. If
149 journal files are not accessible to the caller, this
150 will be silently ignored.</para>
153 <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
154 for an example of how to iterate through the journal
155 after opening it with
156 <function>sd_journal_open()</function>.</para>
158 <para>A journal context object returned by
159 <function>sd_journal_open()</function> references a
160 specific journal entry as <emphasis>current</emphasis> entry,
161 similar to a file seek index in a classic file system
162 file, but without absolute positions. It may be
164 <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
166 <citerefentry><refentrytitle>sd_journal_seek_head</refentrytitle><manvolnum>3</manvolnum></citerefentry>
167 and related calls. The current entry position may be
168 exported in <emphasis>cursor</emphasis> strings, as accessible
170 <citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>. Cursor
171 strings may be used to globally identify a specific
172 journal entry in a stable way and then later to seek
173 to it (or if the specific entry is not available
174 locally, to its closest entry in time)
175 <citerefentry><refentrytitle>sd_journal_seek_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
177 <para>Notification of journal changes is available via
178 <function>sd_journal_get_fd()</function> and related
183 <title>Return Value</title>
185 <para>The <function>sd_journal_open()</function>,
186 <function>sd_journal_open_directory()</function>, and
187 <function>sd_journal_open_files()</function> calls
188 return 0 on success or a negative errno-style error
189 code. <function>sd_journal_close()</function> returns
196 <para>The <function>sd_journal_open()</function>,
197 <function>sd_journal_open_directory()</function> and
198 <function>sd_journal_close()</function> interfaces are
199 available as a shared library, which can be compiled and
201 <constant>libsystemd-journal</constant> <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
206 <title>History</title>
208 <para><function>sd_journal_open()</function>,
209 <function>sd_journal_close()</function>,
210 <constant>SD_JOURNAL_LOCAL_ONLY</constant>,
211 <constant>SD_JOURNAL_RUNTIME_ONLY</constant>,
212 <constant>SD_JOURNAL_SYSTEM_ONLY</constant> were added
213 in systemd-38.</para>
215 <para><function>sd_journal_open_directory()</function>
216 was added in systemd-187.</para>
218 <para><constant>SD_JOURNAL_SYSTEM</constant>,
219 <constant>SD_JOURNAL_CURRENT_USER</constant>,
220 and <function>sd_journal_open_files()</function>
221 were added in systemd-205.
222 <constant>SD_JOURNAL_SYSTEM_ONLY</constant>
223 was deprecated.</para>
227 <title>See Also</title>
230 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
231 <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
232 <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
233 <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>