178 lines
7.2 KiB
XML
178 lines
7.2 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!--
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SPDX-License-Identifier: LGPL-2.1+
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This file is part of systemd.
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Copyright 2012 Lennart Poettering
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systemd is free software; you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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systemd is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with systemd; If not, see <http://www.gnu.org/licenses/>.
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-->
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<refentry id="sd_journal_seek_head">
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<refentryinfo>
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<title>sd_journal_seek_head</title>
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<productname>systemd</productname>
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<authorgroup>
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<author>
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<contrib>Developer</contrib>
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<firstname>Lennart</firstname>
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<surname>Poettering</surname>
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<email>lennart@poettering.net</email>
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</author>
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</authorgroup>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_journal_seek_head</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sd_journal_seek_head</refname>
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<refname>sd_journal_seek_tail</refname>
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<refname>sd_journal_seek_monotonic_usec</refname>
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<refname>sd_journal_seek_realtime_usec</refname>
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<refname>sd_journal_seek_cursor</refname>
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<refpurpose>Seek to a position in the
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journal</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <systemd/sd-journal.h></funcsynopsisinfo>
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<funcprototype>
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<funcdef>int <function>sd_journal_seek_head</function></funcdef>
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<paramdef>sd_journal *<parameter>j</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_journal_seek_tail</function></funcdef>
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<paramdef>sd_journal *<parameter>j</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_journal_seek_monotonic_usec</function></funcdef>
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<paramdef>sd_journal *<parameter>j</parameter></paramdef>
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<paramdef>sd_id128_t <parameter>boot_id</parameter></paramdef>
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<paramdef>uint64_t <parameter>usec</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_journal_seek_realtime_usec</function></funcdef>
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<paramdef>sd_journal *<parameter>j</parameter></paramdef>
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<paramdef>uint64_t <parameter>usec</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_journal_seek_cursor</function></funcdef>
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<paramdef>sd_journal *<parameter>j</parameter></paramdef>
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<paramdef>const char *<parameter>cursor</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><function>sd_journal_seek_head()</function> seeks to the
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beginning of the journal, i.e. the oldest available entry.</para>
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<para>Similarly, <function>sd_journal_seek_tail()</function> may
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be used to seek to the end of the journal, i.e. the most recent
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available entry.</para>
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<para><function>sd_journal_seek_monotonic_usec()</function> seeks
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to the entry with the specified monotonic timestamp, i.e.
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<constant>CLOCK_MONOTONIC</constant>. Since monotonic time
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restarts on every reboot a boot ID needs to be specified as
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well.</para>
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<para><function>sd_journal_seek_realtime_usec()</function> seeks
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to the entry with the specified realtime (wallclock) timestamp,
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i.e. <constant>CLOCK_REALTIME</constant>. Note that the realtime
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clock is not necessarily monotonic. If a realtime timestamp is
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ambiguous, it is not defined which position is sought to.</para>
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<para><function>sd_journal_seek_cursor()</function> seeks to the
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entry located at the specified cursor string. For details on
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cursors, see
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<citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
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If no entry matching the specified cursor is found the call will
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seek to the next closest entry (in terms of time) instead. To
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verify whether the newly selected entry actually matches the
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cursor, use
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<citerefentry><refentrytitle>sd_journal_test_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
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<para>Note that these calls do not actually make any entry the new
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current entry, this needs to be done in a separate step with a
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subsequent
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<citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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invocation (or a similar call). Only then, entry data may be
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retrieved via
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<citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
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If no entry exists that matches exactly the specified seek
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address, the next closest is sought to. If
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<citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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is used, the closest following entry will be sought to, if
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<citerefentry><refentrytitle>sd_journal_previous</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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is used the closest preceding entry is sought to.</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para>The functions return 0 on success or a negative errno-style
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error code.</para>
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</refsect1>
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<refsect1>
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<title>Notes</title>
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<para>All functions listed here are thread-agnostic and only a single thread may operate
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on a given <structname>sd_journal</structname> object.</para>
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<para>The <function>sd_journal_seek_head()</function>,
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<function>sd_journal_seek_tail()</function>,
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<function>sd_journal_seek_monotonic_usec()</function>,
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<function>sd_journal_seek_realtime_usec()</function>,
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and <function>sd_journal_seek_cursor()</function>
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interfaces are available as a shared library, which can
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be compiled and linked to with the
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<constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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file.</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_journal_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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