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_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><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.
 139                 </para>
 140
 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>
 146
 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>
 151
 152                 <para>See
 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>
 157
 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
 163                 altered with
 164                 <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 165                 and
 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
 169                 via
 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>
 176
 177                 <para>Notification of journal changes is available via
 178                 <function>sd_journal_get_fd()</function> and related
 179                 calls.</para>
 180         </refsect1>
 181
 182         <refsect1>
 183                 <title>Return Value</title>
 184
 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
 190                 nothing.</para>
 191         </refsect1>
 192
 193         <refsect1>
 194                 <title>Notes</title>
 195
 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
 200                 linked to with the
 201                 <constant>libsystemd-journal</constant> <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 202                 file.</para>
 203         </refsect1>
 204
 205         <refsect1>
 206                 <title>History</title>
 207
 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>
 214
 215                 <para><function>sd_journal_open_directory()</function>
 216                 was added in systemd-187.</para>
 217
 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>
 224         </refsect1>
 225
 226         <refsect1>
 227                 <title>See Also</title>
 228
 229                 <para>
 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>
 234                 </para>
 235         </refsect1>
 236
 237 </refentry>