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_close</refname>
  49                 <refname>sd_journal</refname>
  50                 <refname>SD_JOURNAL_LOCAL_ONLY</refname>
  51                 <refname>SD_JOURNAL_RUNTIME_ONLY</refname>
  52                 <refname>SD_JOURNAL_SYSTEM_ONLY</refname>
  53                 <refpurpose>Open the system journal for reading</refpurpose>
  54         </refnamediv>
  55
  56         <refsynopsisdiv>
  57                 <funcsynopsis>
  58                         <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>
  59
  60                         <funcprototype>
  61                                 <funcdef>int <function>sd_journal_open</function></funcdef>
  62                                 <paramdef>sd_journal** <parameter>ret</parameter></paramdef>
  63                                 <paramdef>int <parameter>flags</parameter></paramdef>
  64                         </funcprototype>
  65
  66                         <funcprototype>
  67                                 <funcdef>int <function>sd_journal_open_directory</function></funcdef>
  68                                 <paramdef>sd_journal** <parameter>ret</parameter></paramdef>
  69                                 <paramdef>const char* <parameter>path</parameter></paramdef>
  70                                 <paramdef>int <parameter>flags</parameter></paramdef>
  71                         </funcprototype>
  72
  73                         <funcprototype>
  74                                 <funcdef>int <function>sd_journal_close</function></funcdef>
  75                                 <paramdef>sd_journal* <parameter>j</parameter></paramdef>
  76                         </funcprototype>
  77                 </funcsynopsis>
  78         </refsynopsisdiv>
  79
  80         <refsect1>
  81                 <title>Description</title>
  82
  83                 <para><function>sd_journal_open()</function> opens the
  84                 the log journal for reading. It will find all journal
  85                 files automatically and interleave them automatically
  86                 when reading. As first argument it takes a pointer to
  87                 a <literal>sd_journal</literal> pointer, which on
  88                 success will contain journal context object afterwards. The
  89                 second argument is a flags field, which may consist of
  90                 the following flags ORed together:
  91                 <literal>SD_JOURNAL_LOCAL_ONLY</literal> makes sure
  92                 only journal files generated on the local machine will
  93                 be opened. <literal>SD_JOURNAL_RUNTIME_ONLY</literal>
  94                 makes sure only volatile journal files will be opened,
  95                 excluding those which are stored on persistent
  96                 storage. <literal>SD_JOURNAL_SYSTEM_ONLY</literal>
  97                 will ensure that only journal files of system services
  98                 and the kernel (in opposition to user session processes) will
  99                 be opened.</para>
 100
 101                 <para><function>sd_journal_open_directory()</function>
 102                 is similar to <function>sd_journal_open()</function>
 103                 but takes an absolute directory path as argument. All
 104                 journal files in this directory will be opened and
 105                 interleaved automatically. This call also takes a
 106                 flags argument, but it must be passed as 0 as no flags
 107                 are currently understood for this call.</para>
 108
 109                 <para><function>sd_journal_close()</function> will
 110                 close the journal context allocated with
 111                 <function>sd_journal_open()</function> or
 112                 <function>sd_journal_open_directory()</function> and
 113                 free its resources.</para>
 114
 115                 <para>When opening the journal only journal files
 116                 accessible to the calling user will be opened. If
 117                 journal files are not accessible to the caller this
 118                 will be silently ignored.</para>
 119
 120                 <para>See
 121                 <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 122                 for an example how to iterate through the journal
 123                 after opening it it with
 124                 <function>sd_journal_open()</function>.</para>
 125
 126                 <para>A journal context object returned by
 127                 <function>sd_journal_open()</function> references a
 128                 specific journal entry as <emphasis>current</emphasis> entry,
 129                 similar to a file seek index in a classic file system
 130                 file, but without absolute positions. It may be
 131                 altered with
 132                 <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 133                 and
 134                 <citerefentry><refentrytitle>sd_journal_seek_head</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 135                 and related calls. The current entry position may be
 136                 exported in <emphasis>cursor</emphasis> strings, as accessible
 137                 via
 138                 <citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>. Cursor
 139                 strings may be used to globally identify a specific
 140                 journal entry in a stable way and then later to seek
 141                 to it (or if the specific entry is not available
 142                 locally, to its closest entry in time)
 143                 <citerefentry><refentrytitle>sd_journal_seek_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
 144
 145                 <para>Notification of journal changes is available via
 146                 <function>sd_journal_get_fd()</function> and related
 147                 calls.</para>
 148         </refsect1>
 149
 150         <refsect1>
 151                 <title>Return Value</title>
 152
 153                 <para>The <function>sd_journal_open()</function> and
 154                 <function>sd_journal_open_directory()</function> calls
 155                 return 0 on success or a negative errno-style error
 156                 code. <function>sd_journal_close()</function> returns
 157                 nothing.</para>
 158         </refsect1>
 159
 160         <refsect1>
 161                 <title>Notes</title>
 162
 163                 <para>The <function>sd_journal_open()</function>,
 164                 <function>sd_journal_open_directory()</function> and
 165                 <function>sd_journal_close()</function> interfaces are
 166                 available as shared library, which can be compiled and
 167                 linked to with the
 168                 <literal>libsystemd-journal</literal>
 169                 <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 170                 file.</para>
 171         </refsect1>
 172
 173         <refsect1>
 174                 <title>See Also</title>
 175
 176                 <para>
 177                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 178                         <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 179                         <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 180                         <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 181                 </para>
 182         </refsect1>
 183
 184 </refentry>