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
   5 <!--
   6   SPDX-License-Identifier: LGPL-2.1+
   7 -->
   8
   9 <refentry id="sd_journal_seek_head" xmlns:xi="http://www.w3.org/2001/XInclude">
  10
  11   <refentryinfo>
  12     <title>sd_journal_seek_head</title>
  13     <productname>systemd</productname>
  14   </refentryinfo>
  15
  16   <refmeta>
  17     <refentrytitle>sd_journal_seek_head</refentrytitle>
  18     <manvolnum>3</manvolnum>
  19   </refmeta>
  20
  21   <refnamediv>
  22     <refname>sd_journal_seek_head</refname>
  23     <refname>sd_journal_seek_tail</refname>
  24     <refname>sd_journal_seek_monotonic_usec</refname>
  25     <refname>sd_journal_seek_realtime_usec</refname>
  26     <refname>sd_journal_seek_cursor</refname>
  27     <refpurpose>Seek to a position in the
  28     journal</refpurpose>
  29   </refnamediv>
  30
  31   <refsynopsisdiv>
  32     <funcsynopsis>
  33       <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>
  34
  35       <funcprototype>
  36         <funcdef>int <function>sd_journal_seek_head</function></funcdef>
  37         <paramdef>sd_journal *<parameter>j</parameter></paramdef>
  38       </funcprototype>
  39
  40       <funcprototype>
  41         <funcdef>int <function>sd_journal_seek_tail</function></funcdef>
  42         <paramdef>sd_journal *<parameter>j</parameter></paramdef>
  43       </funcprototype>
  44
  45       <funcprototype>
  46         <funcdef>int <function>sd_journal_seek_monotonic_usec</function></funcdef>
  47         <paramdef>sd_journal *<parameter>j</parameter></paramdef>
  48         <paramdef>sd_id128_t <parameter>boot_id</parameter></paramdef>
  49         <paramdef>uint64_t <parameter>usec</parameter></paramdef>
  50       </funcprototype>
  51
  52       <funcprototype>
  53         <funcdef>int <function>sd_journal_seek_realtime_usec</function></funcdef>
  54         <paramdef>sd_journal *<parameter>j</parameter></paramdef>
  55         <paramdef>uint64_t <parameter>usec</parameter></paramdef>
  56       </funcprototype>
  57
  58       <funcprototype>
  59         <funcdef>int <function>sd_journal_seek_cursor</function></funcdef>
  60         <paramdef>sd_journal *<parameter>j</parameter></paramdef>
  61         <paramdef>const char *<parameter>cursor</parameter></paramdef>
  62       </funcprototype>
  63     </funcsynopsis>
  64   </refsynopsisdiv>
  65
  66   <refsect1>
  67     <title>Description</title>
  68
  69     <para><function>sd_journal_seek_head()</function> seeks to the beginning of the journal, i.e. to the
  70     position before the oldest available entry.</para>
  71
  72     <para>Similarly, <function>sd_journal_seek_tail()</function> may be used to seek to the end of the
  73     journal, i.e. the position after the most recent available entry.</para>
  74
  75     <para><function>sd_journal_seek_monotonic_usec()</function> seeks to a position with the specified
  76     monotonic timestamp, i.e.  <constant>CLOCK_MONOTONIC</constant>. Since monotonic time restarts on every
  77     reboot a boot ID needs to be specified as well.</para>
  78
  79     <para><function>sd_journal_seek_realtime_usec()</function> seeks to a position with the specified
  80     realtime (wallclock) timestamp, i.e. <constant>CLOCK_REALTIME</constant>. Note that the realtime clock is
  81     not necessarily monotonic. If a realtime timestamp is ambiguous, it is not defined which position is
  82     sought to.</para>
  83
  84     <para><function>sd_journal_seek_cursor()</function> seeks to the position at the specified cursor
  85     string. For details on cursors, see
  86     <citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
  87     If no entry matching the specified cursor is found the call will seek to the next closest entry (in terms
  88     of time) instead. To verify whether the newly selected entry actually matches the cursor, use
  89     <citerefentry><refentrytitle>sd_journal_test_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
  90
  91     <para>Note that these calls do not actually make any entry the new current entry, this needs to be done
  92     in a separate step with a subsequent
  93     <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  94     invocation (or a similar call). Only then, entry data may be retrieved via
  95     <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  96     or an entry cursor be retrieved via
  97     <citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
  98     If no entry exists that matches exactly the specified seek address, the next closest is sought to. If
  99     <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry> is
 100     used, the closest following entry will be sought to, if
 101     <citerefentry><refentrytitle>sd_journal_previous</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 102     is used the closest preceding entry is sought to.</para>
 103   </refsect1>
 104
 105   <refsect1>
 106     <title>Return Value</title>
 107
 108     <para>The functions return 0 on success or a negative errno-style
 109     error code.</para>
 110   </refsect1>
 111
 112   <refsect1>
 113     <title>Notes</title>
 114
 115     <xi:include href="threads-aware.xml" xpointer="strict"/>
 116
 117     <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
 118   </refsect1>
 119
 120   <refsect1>
 121     <title>See Also</title>
 122
 123     <para>
 124       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 125       <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 126       <citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 127       <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 128       <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 129       <citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 130       <citerefentry><refentrytitle>sd_journal_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 131     </para>
 132   </refsect1>
 133
 134 </refentry>