systemd/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">

<!--
  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>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><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>