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[elogind.git] / man / sd_journal_open.xml
1 <?xml version='1.0'?> <!--*-nxml-*-->
2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
3         "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
4
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8   Copyright 2012 Lennart Poettering
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23
24 <refentry id="sd_journal_open">
25
26         <refentryinfo>
27                 <title>sd_journal_open</title>
28                 <productname>systemd</productname>
29
30                 <authorgroup>
31                         <author>
32                                 <contrib>Developer</contrib>
33                                 <firstname>Lennart</firstname>
34                                 <surname>Poettering</surname>
35                                 <email>lennart@poettering.net</email>
36                         </author>
37                 </authorgroup>
38         </refentryinfo>
39
40         <refmeta>
41                 <refentrytitle>sd_journal_open</refentrytitle>
42                 <manvolnum>3</manvolnum>
43         </refmeta>
44
45         <refnamediv>
46                 <refname>sd_journal_open</refname>
47                 <refname>sd_journal_open_directory</refname>
48                 <refname>sd_journal_open_files</refname>
49                 <refname>sd_journal_open_container</refname>
50                 <refname>sd_journal_close</refname>
51                 <refname>sd_journal</refname>
52                 <refname>SD_JOURNAL_LOCAL_ONLY</refname>
53                 <refname>SD_JOURNAL_RUNTIME_ONLY</refname>
54                 <refname>SD_JOURNAL_SYSTEM</refname>
55                 <refname>SD_JOURNAL_CURRENT_USER</refname>
56                 <refpurpose>Open the system journal for reading</refpurpose>
57         </refnamediv>
58
59         <refsynopsisdiv>
60                 <funcsynopsis>
61                         <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>
62
63                         <funcprototype>
64                                 <funcdef>int <function>sd_journal_open</function></funcdef>
65                                 <paramdef>sd_journal** <parameter>ret</parameter></paramdef>
66                                 <paramdef>int <parameter>flags</parameter></paramdef>
67                         </funcprototype>
68
69                         <funcprototype>
70                                 <funcdef>int <function>sd_journal_open_directory</function></funcdef>
71                                 <paramdef>sd_journal** <parameter>ret</parameter></paramdef>
72                                 <paramdef>const char* <parameter>path</parameter></paramdef>
73                                 <paramdef>int <parameter>flags</parameter></paramdef>
74                         </funcprototype>
75
76                         <funcprototype>
77                                 <funcdef>int <function>sd_journal_open_files</function></funcdef>
78                                 <paramdef>sd_journal** <parameter>ret</parameter></paramdef>
79                                 <paramdef>const char** <parameter>paths</parameter></paramdef>
80                                 <paramdef>int <parameter>flags</parameter></paramdef>
81                         </funcprototype>
82
83                         <funcprototype>
84                                 <funcdef>int <function>sd_journal_open_container</function></funcdef>
85                                 <paramdef>sd_journal** <parameter>ret</parameter></paramdef>
86                                 <paramdef>const char* <parameter>machine</parameter></paramdef>
87                                 <paramdef>int <parameter>flags</parameter></paramdef>
88                         </funcprototype>
89
90                         <funcprototype>
91                                 <funcdef>void <function>sd_journal_close</function></funcdef>
92                                 <paramdef>sd_journal* <parameter>j</parameter></paramdef>
93                         </funcprototype>
94                 </funcsynopsis>
95         </refsynopsisdiv>
96
97         <refsect1>
98                 <title>Description</title>
99
100                 <para><function>sd_journal_open()</function> opens
101                 the log journal for reading. It will find all journal
102                 files automatically and interleave them automatically
103                 when reading. As first argument it takes a pointer to
104                 a <varname>sd_journal</varname> pointer, which on
105                 success will contain a journal context object. The
106                 second argument is a flags field, which may consist of
107                 the following flags ORed together:
108                 <constant>SD_JOURNAL_LOCAL_ONLY</constant> makes sure
109                 only journal files generated on the local machine will
110                 be opened. <constant>SD_JOURNAL_RUNTIME_ONLY</constant>
111                 makes sure only volatile journal files will be opened,
112                 excluding those which are stored on persistent
113                 storage. <constant>SD_JOURNAL_SYSTEM</constant>
114                 will cause journal files of system services and the
115                 kernel (in opposition to user session processes) to
116                 be opened. <constant>SD_JOURNAL_CURRENT_USER</constant>
117                 will cause journal files of the current user to be
118                 opened. If neither <constant>SD_JOURNAL_SYSTEM</constant>
119                 nor <constant>SD_JOURNAL_CURRENT_USER</constant> are
120                 specified, all journal file types will be opened.</para>
121
122                 <para><function>sd_journal_open_directory()</function>
123                 is similar to <function>sd_journal_open()</function>
124                 but takes an absolute directory path as argument. All
125                 journal files in this directory 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.</para>
129
130                 <para><function>sd_journal_open_files()</function>
131                 is similar to <function>sd_journal_open()</function>
132                 but takes a <constant>NULL</constant>-terminated list
133                 of file paths to open. All files will be opened and
134                 interleaved automatically. This call also takes a
135                 flags argument, but it must be passed as 0 as no flags
136                 are currently understood for this call. Please note
137                 that in the case of a live journal, this function is only
138                 useful for debugging, because individual journal files
139                 can be rotated at any moment, and the opening of
140                 specific files is inherently racy.</para>
141
142                 <para><function>sd_journal_open_container()</function>
143                 is similar to <function>sd_journal_open()</function>
144                 but opens the journal files of a running
145                 OS container. The specified machine name refers to a
146                 container that is registered with
147                 <citerefentry><refentrytitle>systemd-machined</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
148
149                 <para><varname>sd_journal</varname> objects cannot be
150                 used in the child after a fork. Functions which take a
151                 journal object as an argument
152                 (<function>sd_journal_next()</function> and others)
153                 will return <constant>-ECHILD</constant> after a fork.
154                 </para>
155
156                 <para><function>sd_journal_close()</function> will
157                 close the journal context allocated with
158                 <function>sd_journal_open()</function> or
159                 <function>sd_journal_open_directory()</function> and
160                 free its resources.</para>
161
162                 <para>When opening the journal only journal files
163                 accessible to the calling user will be opened. If
164                 journal files are not accessible to the caller, this
165                 will be silently ignored.</para>
166
167                 <para>See
168                 <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
169                 for an example of how to iterate through the journal
170                 after opening it with
171                 <function>sd_journal_open()</function>.</para>
172
173                 <para>A journal context object returned by
174                 <function>sd_journal_open()</function> references a
175                 specific journal entry as <emphasis>current</emphasis> entry,
176                 similar to a file seek index in a classic file system
177                 file, but without absolute positions. It may be
178                 altered with
179                 <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
180                 and
181                 <citerefentry><refentrytitle>sd_journal_seek_head</refentrytitle><manvolnum>3</manvolnum></citerefentry>
182                 and related calls. The current entry position may be
183                 exported in <emphasis>cursor</emphasis> strings, as accessible
184                 via
185                 <citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>. Cursor
186                 strings may be used to globally identify a specific
187                 journal entry in a stable way and then later to seek
188                 to it (or if the specific entry is not available
189                 locally, to its closest entry in time)
190                 <citerefentry><refentrytitle>sd_journal_seek_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
191
192                 <para>Notification of journal changes is available via
193                 <function>sd_journal_get_fd()</function> and related
194                 calls.</para>
195         </refsect1>
196
197         <refsect1>
198                 <title>Return Value</title>
199
200                 <para>The <function>sd_journal_open()</function>,
201                 <function>sd_journal_open_directory()</function>, and
202                 <function>sd_journal_open_files()</function> calls
203                 return 0 on success or a negative errno-style error
204                 code. <function>sd_journal_close()</function> returns
205                 nothing.</para>
206         </refsect1>
207
208         <refsect1>
209                 <title>Notes</title>
210
211                 <para>The <function>sd_journal_open()</function>,
212                 <function>sd_journal_open_directory()</function> and
213                 <function>sd_journal_close()</function> interfaces are
214                 available as a shared library, which can be compiled and
215                 linked to with the
216                 <constant>libsystemd-journal</constant> <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
217                 file.</para>
218         </refsect1>
219
220         <refsect1>
221                 <title>History</title>
222
223                 <para><function>sd_journal_open()</function>,
224                 <function>sd_journal_close()</function>,
225                 <constant>SD_JOURNAL_LOCAL_ONLY</constant>,
226                 <constant>SD_JOURNAL_RUNTIME_ONLY</constant>,
227                 <constant>SD_JOURNAL_SYSTEM_ONLY</constant> were added
228                 in systemd-38.</para>
229
230                 <para><function>sd_journal_open_directory()</function>
231                 was added in systemd-187.</para>
232
233                 <para><constant>SD_JOURNAL_SYSTEM</constant>,
234                 <constant>SD_JOURNAL_CURRENT_USER</constant>,
235                 and <function>sd_journal_open_files()</function>
236                 were added in systemd-205.
237                 <constant>SD_JOURNAL_SYSTEM_ONLY</constant>
238                 was deprecated.</para>
239         </refsect1>
240
241         <refsect1>
242                 <title>See Also</title>
243
244                 <para>
245                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
246                         <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
247                         <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
248                         <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
249                         <citerefentry><refentrytitle>systemd-machined</refentrytitle><manvolnum>8</manvolnum></citerefentry>
250                 </para>
251         </refsect1>
252
253 </refentry>