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<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!--
SPDX-License-Identifier: LGPL-2.1+
Copyright 2012 Lennart Poettering
-->
<refentry id="sd_journal_open">
<refentryinfo>
<title>sd_journal_open</title>
<productname>systemd</productname>
<authorgroup>
<author>
<contrib>Developer</contrib>
<firstname>Lennart</firstname>
<surname>Poettering</surname>
<email>lennart@poettering.net</email>
</author>
</authorgroup>
</refentryinfo>
<refmeta>
<refentrytitle>sd_journal_open</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refname>sd_journal_open</refname>
<refname>sd_journal_open_directory</refname>
<refname>sd_journal_open_directory_fd</refname>
<refname>sd_journal_open_files</refname>
<refname>sd_journal_open_files_fd</refname>
<refname>sd_journal_close</refname>
<refname>sd_journal</refname>
<refname>SD_JOURNAL_LOCAL_ONLY</refname>
<refname>SD_JOURNAL_RUNTIME_ONLY</refname>
<refname>SD_JOURNAL_SYSTEM</refname>
<refname>SD_JOURNAL_CURRENT_USER</refname>
<refname>SD_JOURNAL_OS_ROOT</refname>
<refpurpose>Open the system journal for reading</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>#include <systemd/sd-journal.h></funcsynopsisinfo>
<funcprototype>
<funcdef>int <function>sd_journal_open</function></funcdef>
<paramdef>sd_journal **<parameter>ret</parameter></paramdef>
<paramdef>int <parameter>flags</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_journal_open_directory</function></funcdef>
<paramdef>sd_journal **<parameter>ret</parameter></paramdef>
<paramdef>const char *<parameter>path</parameter></paramdef>
<paramdef>int <parameter>flags</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_journal_open_directory_fd</function></funcdef>
<paramdef>sd_journal **<parameter>ret</parameter></paramdef>
<paramdef>int <parameter>fd</parameter></paramdef>
<paramdef>int <parameter>flags</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_journal_open_files</function></funcdef>
<paramdef>sd_journal **<parameter>ret</parameter></paramdef>
<paramdef>const char **<parameter>paths</parameter></paramdef>
<paramdef>int <parameter>flags</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_journal_open_files_fd</function></funcdef>
<paramdef>sd_journal **<parameter>ret</parameter></paramdef>
<paramdef>int <parameter>fds[]</parameter></paramdef>
<paramdef>unsigned <parameter>n_fds</parameter></paramdef>
<paramdef>int <parameter>flags</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>void <function>sd_journal_close</function></funcdef>
<paramdef>sd_journal *<parameter>j</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><function>sd_journal_open()</function> opens the log journal
for reading. It will find all journal files automatically and
interleave them automatically when reading. As first argument it
takes a pointer to a <varname>sd_journal</varname> pointer, which,
on success, will contain a journal context object. The second
argument is a flags field, which may consist of the following
flags ORed together: <constant>SD_JOURNAL_LOCAL_ONLY</constant>
makes sure only journal files generated on the local machine will
be opened. <constant>SD_JOURNAL_RUNTIME_ONLY</constant> makes sure
only volatile journal files will be opened, excluding those which
are stored on persistent storage.
<constant>SD_JOURNAL_SYSTEM</constant> will cause journal files of
system services and the kernel (in opposition to user session
processes) to be opened.
<constant>SD_JOURNAL_CURRENT_USER</constant> will cause journal
files of the current user to be opened. If neither
<constant>SD_JOURNAL_SYSTEM</constant> nor
<constant>SD_JOURNAL_CURRENT_USER</constant> are specified, all
journal file types will be opened.</para>
<para><function>sd_journal_open_directory()</function> is similar to <function>sd_journal_open()</function> but
takes an absolute directory path as argument. All journal files in this directory will be opened and interleaved
automatically. This call also takes a flags argument. The flags parameters accepted by this call are
<constant>SD_JOURNAL_OS_ROOT</constant>, <constant>SD_JOURNAL_SYSTEM</constant>, and
<constant>SD_JOURNAL_CURRENT_USER</constant>. If <constant>SD_JOURNAL_OS_ROOT</constant> is specified, journal
files are searched for below the usual <filename>/var/log/journal</filename> and
<filename>/run/log/journal</filename> relative to the specified path, instead of directly beneath it.
The other two flags limit which files are opened, the same as for <function>sd_journal_open()</function>.
</para>
<para><function>sd_journal_open_directory_fd()</function> is similar to
<function>sd_journal_open_directory()</function>, but takes a file descriptor referencing a directory in the file
system instead of an absolute file system path.</para>
<para><function>sd_journal_open_files()</function> is similar to <function>sd_journal_open()</function> but takes a
<constant>NULL</constant>-terminated list of file paths to open. All files will be opened and interleaved
automatically. This call also takes a flags argument, but it must be passed as 0 as no flags are currently
understood for this call. Please note that in the case of a live journal, this function is only useful for
debugging, because individual journal files can be rotated at any moment, and the opening of specific files is
inherently racy.</para>
<para><function>sd_journal_open_files_fd()</function> is similar to <function>sd_journal_open_files()</function>
but takes an array of open file descriptors that must reference journal files, instead of an array of file system
paths. Pass the array of file descriptors as second argument, and the number of array entries in the third. The
flags parameter must be passed as 0.</para>
<para><varname>sd_journal</varname> objects cannot be used in the
child after a fork. Functions which take a journal object as an
argument (<function>sd_journal_next()</function> and others) will
return <constant>-ECHILD</constant> after a fork.
</para>
<para><function>sd_journal_close()</function> will close the
journal context allocated with
<function>sd_journal_open()</function> or
<function>sd_journal_open_directory()</function> and free its
resources.</para>
<para>When opening the journal only journal files accessible to
the calling user will be opened. If journal files are not
accessible to the caller, this will be silently ignored.</para>
<para>See
<citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
for an example of how to iterate through the journal after opening
it with <function>sd_journal_open()</function>.</para>
<para>A journal context object returned by
<function>sd_journal_open()</function> references a specific
journal entry as <emphasis>current</emphasis> entry, similar to a
file seek index in a classic file system file, but without
absolute positions. It may be altered with
<citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
and
<citerefentry><refentrytitle>sd_journal_seek_head</refentrytitle><manvolnum>3</manvolnum></citerefentry>
and related calls. The current entry position may be exported in
<emphasis>cursor</emphasis> strings, as accessible via
<citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
Cursor strings may be used to globally identify a specific journal
entry in a stable way and then later to seek to it (or if the
specific entry is not available locally, to its closest entry in
time)
<citerefentry><refentrytitle>sd_journal_seek_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
<para>Notification of journal changes is available via
<function>sd_journal_get_fd()</function> and related calls.</para>
</refsect1>
<refsect1>
<title>Return Value</title>
<para>The <function>sd_journal_open()</function>,
<function>sd_journal_open_directory()</function>, and
<function>sd_journal_open_files()</function> calls return 0 on
success or a negative errno-style error code.
<function>sd_journal_close()</function> returns nothing.</para>
</refsect1>
<refsect1>
<title>Notes</title>
<para>All functions listed here are thread-agnostic and only a single thread may operate
on a given <structname>sd_journal</structname> object.</para>
<para>The <function>sd_journal_open()</function>,
<function>sd_journal_open_directory()</function> and
<function>sd_journal_close()</function> interfaces are available
as a shared library, which can be compiled and linked to with the
<constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
file.</para>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-machined</refentrytitle><manvolnum>8</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
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