systemd-stable/man/sd_journal_seek_head.xml

<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

<!--
  SPDX-License-Identifier: LGPL-2.1+

  This file is part of systemd.

  Copyright 2012 Lennart Poettering

  systemd is free software; you can redistribute it and/or modify it
  under the terms of the GNU Lesser General Public License as published by
  the Free Software Foundation; either version 2.1 of the License, or
  (at your option) any later version.

  systemd is distributed in the hope that it will be useful, but
  WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public License
  along with systemd; If not, see <http://www.gnu.org/licenses/>.
-->

<refentry id="sd_journal_seek_head">

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

    <authorgroup>
      <author>
        <contrib>Developer</contrib>
        <firstname>Lennart</firstname>
        <surname>Poettering</surname>
        <email>lennart@poettering.net</email>
      </author>
    </authorgroup>
  </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. 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 most recent
    available entry.</para>

    <para><function>sd_journal_seek_monotonic_usec()</function> seeks
    to the entry 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 the entry 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
    entry located 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>.
    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>

    <para>All functions listed here are thread-agnostic and only a single thread may operate
    on a given <structname>sd_journal</structname> object.</para>

    <para>The <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>
    interfaces are available as a shared library, which can
    be compiled and linked to with the
    <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
    file.</para>
  </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>