mirror of
https://github.com/systemd/systemd
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147 lines
6.6 KiB
XML
147 lines
6.6 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refentry id="sd_journal_seek_head" xmlns:xi="http://www.w3.org/2001/XInclude">
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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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</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 beginning of the journal, i.e. to the
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position before the oldest available entry.</para>
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<para>Similarly, <function>sd_journal_seek_tail()</function> may be used to seek to the end of the
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journal, i.e. the position after the most recent available entry.</para>
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<para><function>sd_journal_seek_monotonic_usec()</function> seeks to a position with the specified
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monotonic timestamp, i.e. <constant>CLOCK_MONOTONIC</constant>. Since monotonic time restarts on every
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reboot a boot ID needs to be specified as well.</para>
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<para><function>sd_journal_seek_realtime_usec()</function> seeks to a position with the specified
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realtime (wallclock) timestamp, i.e. <constant>CLOCK_REALTIME</constant>. Note that the realtime clock is
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not necessarily monotonic. If a realtime timestamp is ambiguous, it is not defined which position is
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sought to.</para>
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<para><function>sd_journal_seek_cursor()</function> seeks to the position at the specified cursor
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string. For details on 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 seek to the next closest entry (in terms
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of time) instead.</para>
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<para>Note that these calls do not actually make any entry the new current entry, this needs to be done
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in a separate step with a 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 retrieved via
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<citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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or an entry cursor be retrieved via
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<citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
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If no entry exists that matches exactly the specified seek address, the next closest is sought to. If
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<citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry> is
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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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<para>After the seek is done, and
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<citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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or a similar call has been made,
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<citerefentry><refentrytitle>sd_journal_test_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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may be used to verify whether the newly selected entry actually matches the cursor.
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</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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<xi:include href="threads-aware.xml" xpointer="strict"/>
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<xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
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</refsect1>
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<refsect1>
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<title>History</title>
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<para><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>, and
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<function>sd_journal_seek_cursor()</function> were added in version 187.</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para><simplelist type="inline">
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<member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd_journal_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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</simplelist></para>
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</refsect1>
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</refentry>
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