221 lines
11 KiB
XML
221 lines
11 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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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_add_match">
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<refentryinfo>
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<title>sd_journal_add_match</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_add_match</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_add_match</refname>
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<refname>sd_journal_add_disjunction</refname>
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<refname>sd_journal_add_conjunction</refname>
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<refname>sd_journal_flush_matches</refname>
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<refpurpose>Add or remove entry matches</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_add_match</function></funcdef>
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<paramdef>sd_journal *<parameter>j</parameter></paramdef>
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<paramdef>const void *<parameter>data</parameter></paramdef>
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<paramdef>size_t <parameter>size</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_journal_add_disjunction</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_add_conjunction</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>void <function>sd_journal_flush_matches</function></funcdef>
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<paramdef>sd_journal *<parameter>j</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_add_match()</function> adds
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a match by which to filter the entries of the journal
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file. Matches applied with this call will filter what
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can be iterated through and read from the journal file
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via calls like
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<citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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and
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<citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>. Matches
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are of the form <literal>FIELD=value</literal>, where
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the field part is a short uppercase string consisting
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only of 0-9, A-Z and the underscore. It may not begin
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with two underscores or be the empty string. The value
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part may be any value, including binary. If a match is
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applied, only entries with this field set will be
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iterated. Multiple matches may be active at the same
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time: If they apply to different fields, only entries
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with both fields set like this will be iterated. If
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they apply to the same fields, only entries where the
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field takes one of the specified values will be
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iterated. Well known fields are documented in
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<citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>. Whenever
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a new match is added the current entry position is
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reset, and
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<citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry> (or a similar call)
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needs to be called before entries can be read
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again.</para>
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<para><function>sd_journal_add_disjunction()</function>
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may be used to insert a disjunction (i.e. logical OR)
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in the match list. If this call is invoked, all
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previously added matches since the last invocation of
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<function>sd_journal_add_disjunction()</function> or
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<function>sd_journal_add_conjunction()</function> are
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combined in an OR with all matches added afterwards,
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until
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<function>sd_journal_add_disjunction()</function> or
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<function>sd_journal_add_conjunction()</function> is
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invoked again to begin the next OR or AND
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term. </para>
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<para><function>sd_journal_add_conjunction()</function>
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may be used to insert a conjunction (i.e. logical AND)
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in the match list. If this call is invoked, all
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previously added matches since the last invocation of
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<function>sd_journal_add_conjunction()</function> are
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combined in an AND with all matches added afterwards,
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until
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<function>sd_journal_add_conjunction()</function> is
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invoked again to begin the next AND term. The
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combination of
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<function>sd_journal_add_match()</function>,
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<function>sd_journal_add_disjunction()</function> and
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<function>sd_journal_add_conjunction()</function> may
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be used to build complex search terms, even though
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full logical expressions are not available. Note that
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<function>sd_journal_add_conjunction()</function>
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operates one level 'higher' than
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<function>sd_journal_add_disjunction()</function>. It
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is hence possible to build an expression of AND terms,
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consisting of OR terms, consisting of AND terms,
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consisting of OR terms of matches (the latter OR
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expression is implicitly created for matches with the
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same field name, see above).</para>
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<para><function>sd_journal_flush_matches()</function>
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may be used to flush all matches, disjunction and
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conjunction terms again. After this call all filtering
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is removed and all entries in the journal will be
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iterated again.</para>
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<para>Note that filtering via matches only applies to
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the way the journal is read, it has no effect on storage
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on disk.</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para><function>sd_journal_add_match()</function>,
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<function>sd_journal_add_disjunction()</function> and
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<function>sd_journal_add_conjunction()</function>
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return 0 on success or a negative errno-style error
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code. <function>sd_journal_flush_matches()</function>
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returns nothing.</para>
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</refsect1>
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<refsect1>
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<title>Notes</title>
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<para>The <function>sd_journal_add_match()</function>,
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<function>sd_journal_add_disjunction()</function>,
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<function>sd_journal_add_conjunction()</function> and
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<function>sd_journal_flush_matches()</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><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>Examples</title>
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<para>The following example adds matches to a journal
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context object to iterate only through messages
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generated by the Avahi service at the four error log
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levels, plus all messages of the message ID
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03bb1dab98ab4ecfbf6fff2738bdd964 coming from any
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service (this example lacks the necessary error
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checking):</para>
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<programlisting>...
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int add_matches(sd_journal *j) {
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sd_journal_add_match(j, "_SYSTEMD_UNIT=avahi-daemon.service", 0);
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sd_journal_add_match(j, "PRIORITY=0", 0);
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sd_journal_add_match(j, "PRIORITY=1", 0);
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sd_journal_add_match(j, "PRIORITY=2", 0);
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sd_journal_add_match(j, "PRIORITY=3", 0);
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sd_journal_add_disjunction(j);
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sd_journal_add_match(j, "MESSAGE_ID=03bb1dab98ab4ecfbf6fff2738bdd964", 0);
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}</programlisting>
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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>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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