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
   5 <!--
   6   This file is part of systemd.
   7
   8   Copyright 2012 Lennart Poettering
   9
  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
  13   (at your option) any later version.
  14
  15   systemd is distributed in the hope that it will be useful, but
  16   WITHOUT ANY WARRANTY; without even the implied warranty of
  17   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  18   Lesser General Public License for more details.
  19
  20   You should have received a copy of the GNU Lesser General Public License
  21   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  22 -->
  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_close</refname>
  49                 <refpurpose>Open the system journal for reading</refpurpose>
  50         </refnamediv>
  51
  52         <refsynopsisdiv>
  53                 <funcsynopsis>
  54                         <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>
  55
  56                         <funcprototype>
  57                                 <funcdef>int <function>sd_journal_open</function></funcdef>
  58                                 <paramdef>sd_journal** <parameter>ret</parameter></paramdef>
  59                                 <paramdef>int <parameter>flags</parameter></paramdef>
  60                         </funcprototype>
  61
  62                         <funcprototype>
  63                                 <funcdef>int <function>sd_journal_open_directory</function></funcdef>
  64                                 <paramdef>sd_journal** <parameter>ret</parameter></paramdef>
  65                                 <paramdef>const char* <parameter>path</parameter></paramdef>
  66                                 <paramdef>int <parameter>flags</parameter></paramdef>
  67                         </funcprototype>
  68
  69                         <funcprototype>
  70                                 <funcdef>int <function>sd_journal_close</function></funcdef>
  71                                 <paramdef>sd_journal* <parameter>j</parameter></paramdef>
  72                         </funcprototype>
  73                 </funcsynopsis>
  74         </refsynopsisdiv>
  75
  76         <refsect1>
  77                 <title>Description</title>
  78
  79                 <para><function>sd_journal_open()</function> opens the
  80                 the log journal for reading. It will find all journal
  81                 files automatically and interleave them automatically
  82                 when reading. As first argument it takes a pointer to
  83                 a <literal>sd_journal</literal> pointer, which on
  84                 success will contain journal context afterwards. The
  85                 second argument is a flags field, which may consist of
  86                 the following flags ORed together:
  87                 <literal>SD_JOURNAL_LOCAL_ONLY</literal> makes sure
  88                 only journal files generated on the local machine will
  89                 be opened. <literal>SD_JOURNAL_RUNTIME_ONLY</literal>
  90                 makes sure only volatile journal files will be opened,
  91                 excluding those which are stored on persistant
  92                 storage. <literal>SD_JOURNAL_SYSTEM_ONLY</literal>
  93                 will ensure that only journal files of system services
  94                 and the kernel (in opposition to user session processes) will
  95                 be opened.</para>
  96
  97                 <para><function>sd_journal_open_directory()</function>
  98                 is similar to <function>sd_journal_open()</function>
  99                 but takes an absolute directory path as argument. All
 100                 journal files in this directory will be opened and
 101                 interleaved automatically. This call also takes a
 102                 flags argument, but it must be passed as 0 as no flags
 103                 are currently understood for this call.</para>
 104
 105                 <para><function>sd_journal_close()</function> will
 106                 close the journal context allocated with
 107                 <function>sd_journal_open()</function> or
 108                 <function>sd_journal_open_directory()</function> and
 109                 free its resources.</para>
 110
 111                 <para>When opening the journal only journal files
 112                 accessible to the calling user will be opened. If
 113                 journal files are not accessible to the caller this
 114                 will be silently ignored.</para>
 115
 116                 <para>See
 117                 <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 118                 for an example how to iterate through the journal
 119                 after opening it it with
 120                 <function>sd_journal_open()</function>.</para>
 121
 122                 <para>A journal context object returned by
 123                 <function>sd_journal_open()</function> references a
 124                 specific journal entry as <emphasis>current</emphasis> entry,
 125                 similar to a file seek index in a classic file system
 126                 file, but without absolute positions. It may be
 127                 altered with
 128                 <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 129                 and
 130                 <citerefentry><refentrytitle>sd_journal_seek_head</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 131                 and related calls. The current entry position may be
 132                 exported in <emphasis>cursor</emphasis> strings, as accessible
 133                 via
 134                 <citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>. Cursor
 135                 strings may be used to globally identify a specific
 136                 journal entry in a stable way and then later to seek
 137                 to it (or if the specific entry is not available
 138                 locally, to its closest entry in time)
 139                 <citerefentry><refentrytitle>sd_journal_seek_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
 140
 141                 <para>Notification of journal changes is available via
 142                 <function>sd_journal_get_fd()</function> and related
 143                 calls.</para>
 144         </refsect1>
 145
 146         <refsect1>
 147                 <title>Return Value</title>
 148
 149                 <para>The <function>sd_journal_open()</function> and
 150                 <function>sd_journal_open_directory()</function> calls
 151                 return 0 on success or a negative errno-style error
 152                 code. <function>sd_journal_close()</function> returns
 153                 nothing.</para>
 154         </refsect1>
 155
 156         <refsect1>
 157                 <title>Notes</title>
 158
 159                 <para>The <function>sd_journal_open()</function>,
 160                 <function>sd_journal_open_directory()</function> and
 161                 <function>sd_journal_close()</function> interfaces are
 162                 available as shared library, which can be compiled and
 163                 linked to with the
 164                 <literal>libsystemd-journal</literal>
 165                 <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 166                 file.</para>
 167         </refsect1>
 168
 169         <refsect1>
 170                 <title>See Also</title>
 171
 172                 <para>
 173                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 174                         <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 175                         <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 176                         <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 177                 </para>
 178         </refsect1>
 179
 180 </refentry>