220 lines
9.5 KiB
XML
220 lines
9.5 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 a match by
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which to filter the entries of the journal file. Matches applied
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with this call will filter what can be iterated through and read
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from the journal file 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>.
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Parameter <parameter>data</parameter> must be of the form
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<literal><replaceable>FIELD</replaceable>=<replaceable>value</replaceable></literal>,
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where the <replaceable>FIELD</replaceable> part is a short uppercase string consisting only
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of 0–9, A–Z and the underscore; it may not begin with two underscores or be the empty
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string. The <replaceable>value</replaceable> part may be anything, including binary. Parameter
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<parameter>size</parameter> specifies the number of bytes in <parameter>data</parameter>
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(i.e. the length of <replaceable>FIELD</replaceable>, plus one, plus the length of
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<replaceable>value</replaceable>). Parameter <parameter>size</parameter> may also be
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specified as <constant>0</constant>, in which case <parameter>data</parameter>
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must be a <constant>NUL</constant>-terminated string, and the bytes before the terminating
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zero are used as the match.</para>
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<para>If a match is applied, only entries with this field set
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will be iterated. Multiple matches may be active at the same time:
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If they apply to different fields, only entries with both fields
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set like this will be iterated. If they apply to the same fields,
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only entries where the field takes one of the specified values
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will be iterated. Well known fields are documented in
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<citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
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Whenever a new match is added the current entry position is reset,
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and
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<citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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(or a similar call) 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> may be
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used to insert a disjunction (i.e. logical OR) in the match list.
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If this call is invoked, all previously added matches since the
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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 combined in
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an OR with all matches added afterwards, until
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<function>sd_journal_add_disjunction()</function> or
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<function>sd_journal_add_conjunction()</function> is invoked again
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to begin the next OR or AND term. </para>
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<para><function>sd_journal_add_conjunction()</function> may be
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used to insert a conjunction (i.e. logical AND) in the match list.
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If this call is invoked, all previously added matches since the
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last invocation of
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<function>sd_journal_add_conjunction()</function> are combined in
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an AND with all matches added afterwards, until
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<function>sd_journal_add_conjunction()</function> is invoked again
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to begin the next AND term. The 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 be used to
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build complex search terms, even though full logical expressions
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are not available. Note that
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<function>sd_journal_add_conjunction()</function> operates one
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level 'higher' than
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<function>sd_journal_add_disjunction()</function>. It is hence
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possible to build an expression of AND terms, consisting of OR
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terms, consisting of AND terms, consisting of OR terms of matches
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(the latter OR expression is implicitly created for matches with
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the same field name, see above).</para>
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<para><function>sd_journal_flush_matches()</function> may be used
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to flush all matches, disjunction and conjunction terms again.
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After this call all filtering is removed and all entries in the
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journal will be iterated again.</para>
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<para>Note that filtering via matches only applies to the way the
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journal is read, it has no effect on storage 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>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_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 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>Examples</title>
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<para>The following example adds matches to a journal context
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object to iterate only through messages generated by the Avahi
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service at the four error log levels, plus all messages of the
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message ID 03bb1dab98ab4ecfbf6fff2738bdd964 coming from any
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service (this example lacks the necessary error 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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