systemd/man/sd_journal_seek_head.xml

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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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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.</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>

    <para>After the seek is done, and
    <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    or a similar call has been made,
    <citerefentry><refentrytitle>sd_journal_test_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    may be used to verify whether the newly selected entry actually matches the cursor.
    </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>History</title>
    <para><function>sd_journal_seek_head()</function>,
    <function>sd_journal_seek_tail()</function>,
    <function>sd_journal_seek_monotonic_usec()</function>,
    <function>sd_journal_seek_realtime_usec()</function>, and
    <function>sd_journal_seek_cursor()</function> were added in version 187.</para>
  </refsect1>

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

    <para><simplelist type="inline">
      <member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd_journal_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
    </simplelist></para>
  </refsect1>

</refentry>