man/sd_journal_seek_head.xml

   1 <?xml version='1.0'?> <!--*-nxml-*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4 <!-- SPDX-License-Identifier: LGPL-2.1+ -->
   5
   6 <refentry id="sd_journal_seek_head" xmlns:xi="http://www.w3.org/2001/XInclude">
   7
   8   <refentryinfo>
   9     <title>sd_journal_seek_head</title>
  10     <productname>systemd</productname>
  11   </refentryinfo>
  12
  13   <refmeta>
  14     <refentrytitle>sd_journal_seek_head</refentrytitle>
  15     <manvolnum>3</manvolnum>
  16   </refmeta>
  17
  18   <refnamediv>
  19     <refname>sd_journal_seek_head</refname>
  20     <refname>sd_journal_seek_tail</refname>
  21     <refname>sd_journal_seek_monotonic_usec</refname>
  22     <refname>sd_journal_seek_realtime_usec</refname>
  23     <refname>sd_journal_seek_cursor</refname>
  24     <refpurpose>Seek to a position in the
  25     journal</refpurpose>
  26   </refnamediv>
  27
  28   <refsynopsisdiv>
  29     <funcsynopsis>
  30       <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>
  31
  32       <funcprototype>
  33         <funcdef>int <function>sd_journal_seek_head</function></funcdef>
  34         <paramdef>sd_journal *<parameter>j</parameter></paramdef>
  35       </funcprototype>
  36
  37       <funcprototype>
  38         <funcdef>int <function>sd_journal_seek_tail</function></funcdef>
  39         <paramdef>sd_journal *<parameter>j</parameter></paramdef>
  40       </funcprototype>
  41
  42       <funcprototype>
  43         <funcdef>int <function>sd_journal_seek_monotonic_usec</function></funcdef>
  44         <paramdef>sd_journal *<parameter>j</parameter></paramdef>
  45         <paramdef>sd_id128_t <parameter>boot_id</parameter></paramdef>
  46         <paramdef>uint64_t <parameter>usec</parameter></paramdef>
  47       </funcprototype>
  48
  49       <funcprototype>
  50         <funcdef>int <function>sd_journal_seek_realtime_usec</function></funcdef>
  51         <paramdef>sd_journal *<parameter>j</parameter></paramdef>
  52         <paramdef>uint64_t <parameter>usec</parameter></paramdef>
  53       </funcprototype>
  54
  55       <funcprototype>
  56         <funcdef>int <function>sd_journal_seek_cursor</function></funcdef>
  57         <paramdef>sd_journal *<parameter>j</parameter></paramdef>
  58         <paramdef>const char *<parameter>cursor</parameter></paramdef>
  59       </funcprototype>
  60     </funcsynopsis>
  61   </refsynopsisdiv>
  62
  63   <refsect1>
  64     <title>Description</title>
  65
  66     <para><function>sd_journal_seek_head()</function> seeks to the beginning of the journal, i.e. to the
  67     position before the oldest available entry.</para>
  68
  69     <para>Similarly, <function>sd_journal_seek_tail()</function> may be used to seek to the end of the
  70     journal, i.e. the position after the most recent available entry.</para>
  71
  72     <para><function>sd_journal_seek_monotonic_usec()</function> seeks to a position with the specified
  73     monotonic timestamp, i.e.  <constant>CLOCK_MONOTONIC</constant>. Since monotonic time restarts on every
  74     reboot a boot ID needs to be specified as well.</para>
  75
  76     <para><function>sd_journal_seek_realtime_usec()</function> seeks to a position with the specified
  77     realtime (wallclock) timestamp, i.e. <constant>CLOCK_REALTIME</constant>. Note that the realtime clock is
  78     not necessarily monotonic. If a realtime timestamp is ambiguous, it is not defined which position is
  79     sought to.</para>
  80
  81     <para><function>sd_journal_seek_cursor()</function> seeks to the position at the specified cursor
  82     string. For details on cursors, see
  83     <citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
  84     If no entry matching the specified cursor is found the call will seek to the next closest entry (in terms
  85     of time) instead. To verify whether the newly selected entry actually matches the cursor, use
  86     <citerefentry><refentrytitle>sd_journal_test_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
  87
  88     <para>Note that these calls do not actually make any entry the new current entry, this needs to be done
  89     in a separate step with a subsequent
  90     <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  91     invocation (or a similar call). Only then, entry data may be retrieved via
  92     <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  93     or an entry cursor be retrieved via
  94     <citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
  95     If no entry exists that matches exactly the specified seek address, the next closest is sought to. If
  96     <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry> is
  97     used, the closest following entry will be sought to, if
  98     <citerefentry><refentrytitle>sd_journal_previous</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  99     is used the closest preceding entry is sought to.</para>
 100   </refsect1>
 101
 102   <refsect1>
 103     <title>Return Value</title>
 104
 105     <para>The functions return 0 on success or a negative errno-style
 106     error code.</para>
 107   </refsect1>
 108
 109   <refsect1>
 110     <title>Notes</title>
 111
 112     <xi:include href="threads-aware.xml" xpointer="strict"/>
 113
 114     <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
 115   </refsect1>
 116
 117   <refsect1>
 118     <title>See Also</title>
 119
 120     <para>
 121       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 122       <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 123       <citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 124       <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 125       <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 126       <citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 127       <citerefentry><refentrytitle>sd_journal_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 128     </para>
 129   </refsect1>
 130
 131 </refentry>