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[thirdparty/systemd.git] / man / sd_journal_seek_head.xml

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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<refentry id="sd_journal_seek_head" xmlns:xi="http://www.w3.org/2001/XInclude">

  <refentryinfo>
    <title>sd_journal_seek_head</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>sd_journal_seek_head</refentrytitle>
    <manvolnum>3</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>sd_journal_seek_head</refname>
    <refname>sd_journal_seek_tail</refname>
    <refname>sd_journal_seek_monotonic_usec</refname>
    <refname>sd_journal_seek_realtime_usec</refname>
    <refname>sd_journal_seek_cursor</refname>
    <refpurpose>Seek to a position in the
    journal</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <funcsynopsis>
      <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>

      <funcprototype>
        <funcdef>int <function>sd_journal_seek_head</function></funcdef>
        <paramdef>sd_journal *<parameter>j</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_journal_seek_tail</function></funcdef>
        <paramdef>sd_journal *<parameter>j</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_journal_seek_monotonic_usec</function></funcdef>
        <paramdef>sd_journal *<parameter>j</parameter></paramdef>
        <paramdef>sd_id128_t <parameter>boot_id</parameter></paramdef>
        <paramdef>uint64_t <parameter>usec</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_journal_seek_realtime_usec</function></funcdef>
        <paramdef>sd_journal *<parameter>j</parameter></paramdef>
        <paramdef>uint64_t <parameter>usec</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_journal_seek_cursor</function></funcdef>
        <paramdef>sd_journal *<parameter>j</parameter></paramdef>
        <paramdef>const char *<parameter>cursor</parameter></paramdef>
      </funcprototype>
    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><function>sd_journal_seek_head()</function> seeks to the beginning of the journal, i.e. to the
    position before the oldest available entry.</para>

    <para>Similarly, <function>sd_journal_seek_tail()</function> may be used to seek to the end of the
    journal, i.e. the position after the most recent available entry.</para>

    <para><function>sd_journal_seek_monotonic_usec()</function> seeks to a position with the specified
    monotonic timestamp, i.e.  <constant>CLOCK_MONOTONIC</constant>. Since monotonic time restarts on every
    reboot a boot ID needs to be specified as well.</para>

    <para><function>sd_journal_seek_realtime_usec()</function> seeks to a position with the specified
    realtime (wallclock) timestamp, i.e. <constant>CLOCK_REALTIME</constant>. Note that the realtime clock is
    not necessarily monotonic. If a realtime timestamp is ambiguous, it is not defined which position is
    sought to.</para>

    <para><function>sd_journal_seek_cursor()</function> seeks to the position at the specified cursor
    string. For details on cursors, see
    <citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
    If no entry matching the specified cursor is found the call will seek to the next closest entry (in terms
    of time) instead. To verify whether the newly selected entry actually matches the cursor, use
    <citerefentry><refentrytitle>sd_journal_test_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>

    <para>Note that these calls do not actually make any entry the new current entry, this needs to be done
    in a separate step with a subsequent
    <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    invocation (or a similar call). Only then, entry data may be retrieved via
    <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    or an entry cursor be retrieved via
    <citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
    If no entry exists that matches exactly the specified seek address, the next closest is sought to. If
    <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry> is
    used, the closest following entry will be sought to, if
    <citerefentry><refentrytitle>sd_journal_previous</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    is used the closest preceding entry is sought to.</para>
  </refsect1>

  <refsect1>
    <title>Return Value</title>

    <para>The functions return 0 on success or a negative errno-style
    error code.</para>
  </refsect1>

  <refsect1>
    <title>Notes</title>

    <xi:include href="threads-aware.xml" xpointer="strict"/>

    <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
  </refsect1>

  <refsect1>
    <title>See Also</title>

    <para>
      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_journal_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>