man/sd_journal_seek_head.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_seek_head">
  25
  26         <refentryinfo>
  27                 <title>sd_journal_seek_head</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_seek_head</refentrytitle>
  42                 <manvolnum>3</manvolnum>
  43         </refmeta>
  44
  45         <refnamediv>
  46                 <refname>sd_journal_seek_head</refname>
  47                 <refname>sd_journal_seek_tail</refname>
  48                 <refname>sd_journal_seek_monotonic_usec</refname>
  49                 <refname>sd_journal_seek_realtime_usec</refname>
  50                 <refname>sd_journal_seek_cursor</refname>
  51                 <refpurpose>Seek to a position in the
  52                 journal</refpurpose>
  53         </refnamediv>
  54
  55         <refsynopsisdiv>
  56                 <funcsynopsis>
  57                         <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>
  58
  59                         <funcprototype>
  60                                 <funcdef>int <function>sd_journal_seek_head</function></funcdef>
  61                                 <paramdef>sd_journal *<parameter>j</parameter></paramdef>
  62                         </funcprototype>
  63
  64                         <funcprototype>
  65                                 <funcdef>int <function>sd_journal_seek_tail</function></funcdef>
  66                                 <paramdef>sd_journal *<parameter>j</parameter></paramdef>
  67                         </funcprototype>
  68
  69                         <funcprototype>
  70                                 <funcdef>int <function>sd_journal_seek_monotonic_usec</function></funcdef>
  71                                 <paramdef>sd_journal *<parameter>j</parameter></paramdef>
  72                                 <paramdef>sd_id128_t <parameter>boot_id</parameter></paramdef>
  73                                 <paramdef>uint64_t <parameter>usec</parameter></paramdef>
  74                         </funcprototype>
  75
  76                         <funcprototype>
  77                                 <funcdef>int <function>sd_journal_seek_realtime_usec</function></funcdef>
  78                                 <paramdef>sd_journal *<parameter>j</parameter></paramdef>
  79                                 <paramdef>uint64_t <parameter>usec</parameter></paramdef>
  80                         </funcprototype>
  81
  82                         <funcprototype>
  83                                 <funcdef>int <function>sd_journal_seek_cursor</function></funcdef>
  84                                 <paramdef>sd_journal *<parameter>j</parameter></paramdef>
  85                                 <paramdef>const char *<parameter>cursor</parameter></paramdef>
  86                         </funcprototype>
  87                 </funcsynopsis>
  88         </refsynopsisdiv>
  89
  90         <refsect1>
  91                 <title>Description</title>
  92
  93                 <para><function>sd_journal_seek_head()</function>
  94                 seeks to the beginning of the journal, i.e. the oldest
  95                 available entry.</para>
  96
  97                 <para>Similarly,
  98                 <function>sd_journal_seek_tail()</function> may be
  99                 used to seek to the end of the journal, i.e. the most
 100                 recent available entry.</para>
 101
 102                 <para><function>sd_journal_seek_monotonic_usec()</function>
 103                 seeks to the entry with the specified monotonic
 104                 timestamp,
 105                 i.e. <constant>CLOCK_MONOTONIC</constant>. Since
 106                 monotonic time restarts on every reboot a boot ID
 107                 needs to be specified as well.</para>
 108
 109                 <para><function>sd_journal_seek_realtime_usec()</function>
 110                 seeks to the entry with the specified realtime
 111                 (wallclock) timestamp,
 112                 i.e. <constant>CLOCK_REALTIME</constant>. Note that
 113                 the realtime clock is not necessarily monotonic. If a
 114                 realtime timestamp is ambiguous, it is not defined
 115                 which position is sought to.</para>
 116
 117                 <para><function>sd_journal_seek_cursor()</function>
 118                 seeks to the entry located at the specified cursor
 119                 string. For details on cursors, see
 120                 <citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>. If
 121                 no entry matching the specified cursor is found the
 122                 call will seek to the next closest entry (in terms of
 123                 time) instead. To verify whether the newly selected
 124                 entry actually matches the cursor, use
 125                 <citerefentry><refentrytitle>sd_journal_test_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
 126
 127                 <para>Note that these calls do not actually make any
 128                 entry the new current entry, this needs to be done in
 129                 a separate step with a subsequent
 130                 <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 131                 invocation (or a similar call). Only then, entry data
 132                 may be retrieved via
 133                 <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>. If
 134                 no entry exists that matches exactly the specified
 135                 seek address, the next closest is sought to. If
 136                 <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 137                 is used, the closest following entry will be sought to,
 138                 if
 139                 <citerefentry><refentrytitle>sd_journal_previous</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 140                 is used the closest preceding entry is sought
 141                 to.</para>
 142         </refsect1>
 143
 144         <refsect1>
 145                 <title>Return Value</title>
 146
 147                 <para>The functions return 0 on success or a negative
 148                 errno-style error code.</para>
 149         </refsect1>
 150
 151         <refsect1>
 152                 <title>Notes</title>
 153
 154                 <para>The <function>sd_journal_seek_head()</function>,
 155                 <function>sd_journal_seek_tail()</function>,
 156                 <function>sd_journal_seek_monotonic_usec()</function>,
 157                 <function>sd_journal_seek_realtime_usec()</function>,
 158                 and <function>sd_journal_seek_cursor()</function>
 159                 interfaces are available as a shared library, which can
 160                 be compiled and linked to with the
 161                 <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 162                 file.</para>
 163         </refsect1>
 164
 165         <refsect1>
 166                 <title>See Also</title>
 167
 168                 <para>
 169                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 170                         <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 171                         <citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 172                         <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 173                         <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 174                         <citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 175                         <citerefentry><refentrytitle>sd_journal_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 176                 </para>
 177         </refsect1>
 178
 179 </refentry>