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235 lines
11 KiB
XML
235 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_open">
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<refentryinfo>
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<title>sd_journal_open</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_open</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_open</refname>
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<refname>sd_journal_open_directory</refname>
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<refname>sd_journal_open_directory_fd</refname>
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<refname>sd_journal_open_files</refname>
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<refname>sd_journal_open_files_fd</refname>
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<refname>sd_journal_close</refname>
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<refname>sd_journal</refname>
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<refname>SD_JOURNAL_LOCAL_ONLY</refname>
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<refname>SD_JOURNAL_RUNTIME_ONLY</refname>
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<refname>SD_JOURNAL_SYSTEM</refname>
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<refname>SD_JOURNAL_CURRENT_USER</refname>
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<refname>SD_JOURNAL_OS_ROOT</refname>
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<refpurpose>Open the system journal for reading</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_open</function></funcdef>
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<paramdef>sd_journal **<parameter>ret</parameter></paramdef>
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<paramdef>int <parameter>flags</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_journal_open_directory</function></funcdef>
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<paramdef>sd_journal **<parameter>ret</parameter></paramdef>
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<paramdef>const char *<parameter>path</parameter></paramdef>
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<paramdef>int <parameter>flags</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_journal_open_directory_fd</function></funcdef>
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<paramdef>sd_journal **<parameter>ret</parameter></paramdef>
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<paramdef>int <parameter>fd</parameter></paramdef>
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<paramdef>int <parameter>flags</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_journal_open_files</function></funcdef>
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<paramdef>sd_journal **<parameter>ret</parameter></paramdef>
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<paramdef>const char **<parameter>paths</parameter></paramdef>
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<paramdef>int <parameter>flags</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_journal_open_files_fd</function></funcdef>
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<paramdef>sd_journal **<parameter>ret</parameter></paramdef>
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<paramdef>int <parameter>fds[]</parameter></paramdef>
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<paramdef>unsigned <parameter>n_fds</parameter></paramdef>
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<paramdef>int <parameter>flags</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>void <function>sd_journal_close</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_open()</function> opens the log journal
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for reading. It will find all journal files automatically and
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interleave them automatically when reading. As first argument it
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takes a pointer to a <varname>sd_journal</varname> pointer, which,
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on success, will contain a journal context object. The second
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argument is a flags field, which may consist of the following
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flags ORed together: <constant>SD_JOURNAL_LOCAL_ONLY</constant>
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makes sure only journal files generated on the local machine will
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be opened. <constant>SD_JOURNAL_RUNTIME_ONLY</constant> makes sure
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only volatile journal files will be opened, excluding those which
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are stored on persistent storage.
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<constant>SD_JOURNAL_SYSTEM</constant> will cause journal files of
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system services and the kernel (in opposition to user session
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processes) to be opened.
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<constant>SD_JOURNAL_CURRENT_USER</constant> will cause journal
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files of the current user to be opened. If neither
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<constant>SD_JOURNAL_SYSTEM</constant> nor
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<constant>SD_JOURNAL_CURRENT_USER</constant> are specified, all
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journal file types will be opened.</para>
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<para><function>sd_journal_open_directory()</function> is similar to <function>sd_journal_open()</function> but
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takes an absolute directory path as argument. All journal files in this directory will be opened and interleaved
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automatically. This call also takes a flags argument. The flags parameters accepted by this call are
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<constant>SD_JOURNAL_OS_ROOT</constant>, <constant>SD_JOURNAL_SYSTEM</constant>, and
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<constant>SD_JOURNAL_CURRENT_USER</constant>. If <constant>SD_JOURNAL_OS_ROOT</constant> is specified, journal
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files are searched for below the usual <filename>/var/log/journal</filename> and
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<filename>/run/log/journal</filename> relative to the specified path, instead of directly beneath it.
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The other two flags limit which files are opened, the same as for <function>sd_journal_open()</function>.
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</para>
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<para><function>sd_journal_open_directory_fd()</function> is similar to
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<function>sd_journal_open_directory()</function>, but takes a file descriptor referencing a directory in the file
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system instead of an absolute file system path.</para>
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<para><function>sd_journal_open_files()</function> is similar to <function>sd_journal_open()</function> but takes a
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<constant>NULL</constant>-terminated list of file paths to open. All files will be opened and interleaved
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automatically. This call also takes a flags argument, but it must be passed as 0 as no flags are currently
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understood for this call. Please note that in the case of a live journal, this function is only useful for
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debugging, because individual journal files can be rotated at any moment, and the opening of specific files is
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inherently racy.</para>
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<para><function>sd_journal_open_files_fd()</function> is similar to <function>sd_journal_open_files()</function>
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but takes an array of open file descriptors that must reference journal files, instead of an array of file system
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paths. Pass the array of file descriptors as second argument, and the number of array entries in the third. The
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flags parameter must be passed as 0.</para>
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<para><varname>sd_journal</varname> objects cannot be used in the
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child after a fork. Functions which take a journal object as an
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argument (<function>sd_journal_next()</function> and others) will
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return <constant>-ECHILD</constant> after a fork.
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</para>
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<para><function>sd_journal_close()</function> will close the
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journal context allocated with
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<function>sd_journal_open()</function> or
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<function>sd_journal_open_directory()</function> and free its
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resources.</para>
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<para>When opening the journal only journal files accessible to
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the calling user will be opened. If journal files are not
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accessible to the caller, this will be silently ignored.</para>
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<para>See
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<citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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for an example of how to iterate through the journal after opening
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it with <function>sd_journal_open()</function>.</para>
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<para>A journal context object returned by
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<function>sd_journal_open()</function> references a specific
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journal entry as <emphasis>current</emphasis> entry, similar to a
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file seek index in a classic file system file, but without
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absolute positions. It may be altered with
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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_seek_head</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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and related calls. The current entry position may be exported in
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<emphasis>cursor</emphasis> strings, as accessible via
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<citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
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Cursor strings may be used to globally identify a specific journal
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entry in a stable way and then later to seek to it (or if the
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specific entry is not available locally, to its closest entry in
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time)
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<citerefentry><refentrytitle>sd_journal_seek_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
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<para>Notification of journal changes is available via
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<function>sd_journal_get_fd()</function> and related calls.</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 <function>sd_journal_open()</function>,
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<function>sd_journal_open_directory()</function>, and
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<function>sd_journal_open_files()</function> calls return 0 on
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success or a negative errno-style error code.
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<function>sd_journal_close()</function> 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_open()</function>,
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<function>sd_journal_open_directory()</function> and
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<function>sd_journal_close()</function> interfaces are available
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as a shared library, which can 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_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-machined</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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