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244 lines
12 KiB
XML
244 lines
12 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/4.2/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refentry id="sd_journal_open"
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xmlns:xi="http://www.w3.org/2001/XInclude">
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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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</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_open_namespace</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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<refname>SD_JOURNAL_ALL_NAMESPACES</refname>
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<refname>SD_JOURNAL_INCLUDE_DEFAULT_NAMESPACE</refname>
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<refname>SD_JOURNAL_TAKE_DIRECTORY_FD</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_namespace</function></funcdef>
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<paramdef>sd_journal **<parameter>ret</parameter></paramdef>
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<paramdef>const char *<parameter>namespace</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_namespace()</function> is similar to
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<function>sd_journal_open()</function> but takes an additional <parameter>namespace</parameter> parameter
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that specifies which journal namespace to operate on. If specified as <constant>NULL</constant> the call
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is identical to <function>sd_journal_open()</function>. If non-<constant>NULL</constant> only data from
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the namespace identified by the specified parameter is accessed. This call understands two additional
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flags: if <constant>SD_JOURNAL_ALL_NAMESPACES</constant> is specified the
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<parameter>namespace</parameter> parameter is ignored and all defined namespaces are accessed
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simultaneously; if <constant>SD_JOURNAL_INCLUDE_DEFAULT_NAMESPACE</constant> the specified namespace and
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the default namespace are accessed but no others (this flag has no effect when
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<parameter>namespace</parameter> is passed as <constant>NULL</constant>). For details about journal
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namespaces see
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<citerefentry><refentrytitle>systemd-journald.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</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. In addition to the flags accepted by
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<function>sd_journal_open_directory()</function>, this function also accepts
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<constant>SD_JOURNAL_TAKE_DIRECTORY_FD</constant>. If <constant>SD_JOURNAL_TAKE_DIRECTORY_FD</constant> is
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specified, the function will take the ownership of the specified file descriptor on success, and it will be
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closed by <function>sd_journal_close()</function>, hence the caller of the function must not close the file
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descriptor. When the flag is not specified, <function>sd_journal_close()</function> will not close the file
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descriptor, so the caller should close it after <function>sd_journal_close()</function>.</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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<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_open()</function>,
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<function>sd_journal_open_directory()</function>, and
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<function>sd_journal_close()</function> were added in version 187.</para>
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<para><function>sd_journal_open_files()</function> was added in version 205.</para>
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<para><function>sd_journal_open_directory_fd()</function> and
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<function>sd_journal_open_files_fd()</function> were added in version 230.</para>
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<para><function>sd_journal_open_namespace()</function> was added in version 245.</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>systemd-journald.service</refentrytitle><manvolnum>8</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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</simplelist></para>
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</refsect1>
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</refentry>
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