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>Similar,
  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, i.e. CLOCK_MONOOTONIC. Since monotonic time
 105                 restarts on every reboot a boot ID needs to be
 106                 specified as well.</para>
 107
 108                 <para><function>sd_journal_seek_realtime_usec()</function>
 109                 seeks to the entry with the specified realtime
 110                 (wallclock) timestamp, i.e. CLOCK_REALTIME. Note that
 111                 the realtime clock is not necessary monotonic. If a
 112                 realtime timestamp is ambiguous it is not defined
 113                 which position is sought to.</para>
 114
 115                 <para><function>sd_journal_seek_cursor()</function>
 116                 seeks to the entry located at the specified cursor
 117                 string. For details on cursors see
 118                 <citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>. If
 119                 no entry matching the specified cursor is found the
 120                 call will seek to the next closest entry (in terms of
 121                 time) instead. To verify whether the newly selected
 122                 entry actually matches the cursor use
 123                 <citerefentry><refentrytitle>sd_journal_test_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
 124
 125                 <para>Note that these calls do not actually make any
 126                 entry the new current entry, this needs to be done in
 127                 a separate step with a subsequent
 128                 <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 129                 invocation (or a similar call). Only then entry data
 130                 may be retrieved via
 131                 <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>. If
 132                 no entry exists that matches exactly the specified
 133                 seek address the next closest is sought to. If
 134                 <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 135                 is used the closest following entry will be sought to,
 136                 if
 137                 <citerefentry><refentrytitle>sd_journal_previous</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 138                 is used the closest preceding entry is sought
 139                 to.</para>
 140         </refsect1>
 141
 142         <refsect1>
 143                 <title>Return Value</title>
 144
 145                 <para>The functions return 0 on success or a negative
 146                 errno-style error code.</para>
 147         </refsect1>
 148
 149         <refsect1>
 150                 <title>Notes</title>
 151
 152                 <para>The <function>sd_journal_seek_head()</function>,
 153                 <function>sd_journal_seek_tail()</function>,
 154                 <function>sd_journal_seek_monotonic_usec()</function>,
 155                 <function>sd_journal_seek_realtime_usec()</function>,
 156                 and <function>sd_journal_seek_cursor()</function>
 157                 interfaces are available as shared library, which can
 158                 be compiled and linked to with the
 159                 <literal>libsystemd-journal</literal>
 160                 <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 161                 file.</para>
 162         </refsect1>
 163
 164         <refsect1>
 165                 <title>See Also</title>
 166
 167                 <para>
 168                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 169                         <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 170                         <citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 171                         <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 172                         <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 173                         <citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 174                         <citerefentry><refentrytitle>sd_journal_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 175                 </para>
 176         </refsect1>
 177
 178 </refentry>