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_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>
  56         </refnamediv>
  57
  58         <refsynopsisdiv>
  59                 <funcsynopsis>
  60                         <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>
  61
  62                         <funcprototype>
  63                                 <funcdef>int <function>sd_journal_open</function></funcdef>
  64                                 <paramdef>sd_journal** <parameter>ret</parameter></paramdef>
  65                                 <paramdef>int <parameter>flags</parameter></paramdef>
  66                         </funcprototype>
  67
  68                         <funcprototype>
  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>
  73                         </funcprototype>
  74
  75                         <funcprototype>
  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>
  80                         </funcprototype>
  81
  82                         <funcprototype>
  83                                 <funcdef>void <function>sd_journal_close</function></funcdef>
  84                                 <paramdef>sd_journal* <parameter>j</parameter></paramdef>
  85                         </funcprototype>
  86                 </funcsynopsis>
  87         </refsynopsisdiv>
  88
  89         <refsect1>
  90                 <title>Description</title>
  91
  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>
 113
 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>
 121
 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>
 133
 134                 <para><function>sd_journal_close()</function> will
 135                 close the journal context allocated with
 136                 <function>sd_journal_open()</function> or
 137                 <function>sd_journal_open_directory()</function> and
 138                 free its resources.</para>
 139
 140                 <para>When opening the journal only journal files
 141                 accessible to the calling user will be opened. If
 142                 journal files are not accessible to the caller this
 143                 will be silently ignored.</para>
 144
 145                 <para>See
 146                 <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 147                 for an example of how to iterate through the journal
 148                 after opening it with
 149                 <function>sd_journal_open()</function>.</para>
 150
 151                 <para>A journal context object returned by
 152                 <function>sd_journal_open()</function> references a
 153                 specific journal entry as <emphasis>current</emphasis> entry,
 154                 similar to a file seek index in a classic file system
 155                 file, but without absolute positions. It may be
 156                 altered with
 157                 <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 158                 and
 159                 <citerefentry><refentrytitle>sd_journal_seek_head</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 160                 and related calls. The current entry position may be
 161                 exported in <emphasis>cursor</emphasis> strings, as accessible
 162                 via
 163                 <citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>. Cursor
 164                 strings may be used to globally identify a specific
 165                 journal entry in a stable way and then later to seek
 166                 to it (or if the specific entry is not available
 167                 locally, to its closest entry in time)
 168                 <citerefentry><refentrytitle>sd_journal_seek_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
 169
 170                 <para>Notification of journal changes is available via
 171                 <function>sd_journal_get_fd()</function> and related
 172                 calls.</para>
 173         </refsect1>
 174
 175         <refsect1>
 176                 <title>Return Value</title>
 177
 178                 <para>The <function>sd_journal_open()</function>,
 179                 <function>sd_journal_open_directory()</function>, and
 180                 <function>sd_journal_open_files()</function> calls
 181                 return 0 on success or a negative errno-style error
 182                 code. <function>sd_journal_close()</function> returns
 183                 nothing.</para>
 184         </refsect1>
 185
 186         <refsect1>
 187                 <title>Notes</title>
 188
 189                 <para>The <function>sd_journal_open()</function>,
 190                 <function>sd_journal_open_directory()</function> and
 191                 <function>sd_journal_close()</function> interfaces are
 192                 available as a shared library, which can be compiled and
 193                 linked to with the
 194                 <constant>libsystemd-journal</constant> <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 195                 file.</para>
 196         </refsect1>
 197
 198         <refsect1>
 199                 <title>History</title>
 200
 201                 <para><function>sd_journal_open()</function>,
 202                 <function>sd_journal_close()</function>,
 203                 <constant>SD_JOURNAL_LOCAL_ONLY</constant>,
 204                 <constant>SD_JOURNAL_RUNTIME_ONLY</constant>,
 205                 <constant>SD_JOURNAL_SYSTEM_ONLY</constant> were added
 206                 in systemd-38.</para>
 207
 208                 <para><function>sd_journal_open_directory()</function>
 209                 was added in systemd-187.</para>
 210
 211                 <para><constant>SD_JOURNAL_SYSTEM</constant>,
 212                 <constant>SD_JOURNAL_CURRENT_USER</constant>,
 213                 and <function>sd_journal_open_files()</function>
 214                 were added in systemd-205.
 215                 <constant>SD_JOURNAL_SYSTEM_ONLY</constant>
 216                 was deprecated.</para>
 217         </refsect1>
 218
 219         <refsect1>
 220                 <title>See Also</title>
 221
 222                 <para>
 223                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 224                         <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 225                         <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 226                         <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 227                 </para>
 228         </refsect1>
 229
 230 </refentry>