man/sd_journal_open.xml

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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_directory_fd</refname>
  49     <refname>sd_journal_open_files</refname>
  50     <refname>sd_journal_open_files_fd</refname>
  51     <refname>sd_journal_close</refname>
  52     <refname>sd_journal</refname>
  53     <refname>SD_JOURNAL_LOCAL_ONLY</refname>
  54     <refname>SD_JOURNAL_RUNTIME_ONLY</refname>
  55     <refname>SD_JOURNAL_SYSTEM</refname>
  56     <refname>SD_JOURNAL_CURRENT_USER</refname>
  57     <refname>SD_JOURNAL_OS_ROOT</refname>
  58     <refpurpose>Open the system journal for reading</refpurpose>
  59   </refnamediv>
  60
  61   <refsynopsisdiv>
  62     <funcsynopsis>
  63       <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>
  64
  65       <funcprototype>
  66         <funcdef>int <function>sd_journal_open</function></funcdef>
  67         <paramdef>sd_journal **<parameter>ret</parameter></paramdef>
  68         <paramdef>int <parameter>flags</parameter></paramdef>
  69       </funcprototype>
  70
  71       <funcprototype>
  72         <funcdef>int <function>sd_journal_open_directory</function></funcdef>
  73         <paramdef>sd_journal **<parameter>ret</parameter></paramdef>
  74         <paramdef>const char *<parameter>path</parameter></paramdef>
  75         <paramdef>int <parameter>flags</parameter></paramdef>
  76       </funcprototype>
  77
  78       <funcprototype>
  79         <funcdef>int <function>sd_journal_open_directory_fd</function></funcdef>
  80         <paramdef>sd_journal **<parameter>ret</parameter></paramdef>
  81         <paramdef>int <parameter>fd</parameter></paramdef>
  82         <paramdef>int <parameter>flags</parameter></paramdef>
  83       </funcprototype>
  84
  85       <funcprototype>
  86         <funcdef>int <function>sd_journal_open_files</function></funcdef>
  87         <paramdef>sd_journal **<parameter>ret</parameter></paramdef>
  88         <paramdef>const char **<parameter>paths</parameter></paramdef>
  89         <paramdef>int <parameter>flags</parameter></paramdef>
  90       </funcprototype>
  91
  92       <funcprototype>
  93         <funcdef>int <function>sd_journal_open_files_fd</function></funcdef>
  94         <paramdef>sd_journal **<parameter>ret</parameter></paramdef>
  95         <paramdef>int <parameter>fds[]</parameter></paramdef>
  96         <paramdef>unsigned <parameter>n_fds</parameter></paramdef>
  97         <paramdef>int <parameter>flags</parameter></paramdef>
  98       </funcprototype>
  99
 100       <funcprototype>
 101         <funcdef>void <function>sd_journal_close</function></funcdef>
 102         <paramdef>sd_journal *<parameter>j</parameter></paramdef>
 103       </funcprototype>
 104     </funcsynopsis>
 105   </refsynopsisdiv>
 106
 107   <refsect1>
 108     <title>Description</title>
 109
 110     <para><function>sd_journal_open()</function> opens the log journal
 111     for reading. It will find all journal files automatically and
 112     interleave them automatically when reading. As first argument it
 113     takes a pointer to a <varname>sd_journal</varname> pointer, which,
 114     on success, will contain a journal context object. The second
 115     argument is a flags field, which may consist of the following
 116     flags ORed together: <constant>SD_JOURNAL_LOCAL_ONLY</constant>
 117     makes sure only journal files generated on the local machine will
 118     be opened. <constant>SD_JOURNAL_RUNTIME_ONLY</constant> makes sure
 119     only volatile journal files will be opened, excluding those which
 120     are stored on persistent storage.
 121     <constant>SD_JOURNAL_SYSTEM</constant> will cause journal files of
 122     system services and the kernel (in opposition to user session
 123     processes) to be opened.
 124     <constant>SD_JOURNAL_CURRENT_USER</constant> will cause journal
 125     files of the current user to be opened. If neither
 126     <constant>SD_JOURNAL_SYSTEM</constant> nor
 127     <constant>SD_JOURNAL_CURRENT_USER</constant> are specified, all
 128     journal file types will be opened.</para>
 129
 130     <para><function>sd_journal_open_directory()</function> is similar to <function>sd_journal_open()</function> but
 131     takes an absolute directory path as argument. All journal files in this directory will be opened and interleaved
 132     automatically. This call also takes a flags argument. The only flags parameter accepted by this call is
 133     <constant>SD_JOURNAL_OS_ROOT</constant>. If specified, the journal files are searched below the usual
 134     <filename>/var/log/journal</filename> and <filename>/run/log/journal</filename> relative to the specified path,
 135     instead of directly beneath it.</para>
 136
 137     <para><function>sd_journal_open_directory_fd()</function> is similar to
 138     <function>sd_journal_open_directory()</function>, but takes a file descriptor referencing a directory in the file
 139     system instead of an absolute file system path.</para>
 140
 141     <para><function>sd_journal_open_files()</function> is similar to <function>sd_journal_open()</function> but takes a
 142     <constant>NULL</constant>-terminated list of file paths to open.  All files will be opened and interleaved
 143     automatically. This call also takes a flags argument, but it must be passed as 0 as no flags are currently
 144     understood for this call. Please note that in the case of a live journal, this function is only useful for
 145     debugging, because individual journal files can be rotated at any moment, and the opening of specific files is
 146     inherently racy.</para>
 147
 148     <para><function>sd_journal_open_files_fd()</function> is similar to <function>sd_journal_open_files()</function>
 149     but takes an array of open file descriptors that must reference journal files, instead of an array of file system
 150     paths. Pass the array of file descriptors as second argument, and the number of array entries in the third. The
 151     flags parameter must be passed as 0.</para>
 152
 153     <para><varname>sd_journal</varname> objects cannot be used in the
 154     child after a fork. Functions which take a journal object as an
 155     argument (<function>sd_journal_next()</function> and others) will
 156     return <constant>-ECHILD</constant> after a fork.
 157     </para>
 158
 159     <para><function>sd_journal_close()</function> will close the
 160     journal context allocated with
 161     <function>sd_journal_open()</function> or
 162     <function>sd_journal_open_directory()</function> and free its
 163     resources.</para>
 164
 165     <para>When opening the journal only journal files accessible to
 166     the calling user will be opened. If journal files are not
 167     accessible to the caller, this will be silently ignored.</para>
 168
 169     <para>See
 170     <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 171     for an example of how to iterate through the journal after opening
 172     it with <function>sd_journal_open()</function>.</para>
 173
 174     <para>A journal context object returned by
 175     <function>sd_journal_open()</function> references a specific
 176     journal entry as <emphasis>current</emphasis> entry, similar to a
 177     file seek index in a classic file system file, but without
 178     absolute positions. It may be 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 exported in
 183     <emphasis>cursor</emphasis> strings, as accessible via
 184     <citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 185     Cursor strings may be used to globally identify a specific journal
 186     entry in a stable way and then later to seek to it (or if the
 187     specific entry is not available locally, to its closest entry in
 188     time)
 189     <citerefentry><refentrytitle>sd_journal_seek_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
 190
 191     <para>Notification of journal changes is available via
 192     <function>sd_journal_get_fd()</function> and related calls.</para>
 193   </refsect1>
 194
 195   <refsect1>
 196     <title>Return Value</title>
 197
 198     <para>The <function>sd_journal_open()</function>,
 199     <function>sd_journal_open_directory()</function>, and
 200     <function>sd_journal_open_files()</function> calls return 0 on
 201     success or a negative errno-style error code.
 202     <function>sd_journal_close()</function> returns nothing.</para>
 203   </refsect1>
 204
 205   <refsect1>
 206     <title>Notes</title>
 207
 208     <para>The <function>sd_journal_open()</function>,
 209     <function>sd_journal_open_directory()</function> and
 210     <function>sd_journal_close()</function> interfaces are available
 211     as a shared library, which can be compiled and linked to with the
 212     <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 213     file.</para>
 214   </refsect1>
 215
 216   <refsect1>
 217     <title>See Also</title>
 218
 219     <para>
 220       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 221       <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 222       <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 223       <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 224       <citerefentry><refentrytitle>systemd-machined</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 225     </para>
 226   </refsect1>
 227
 228 </refentry>