systemd/man/sd_journal_open.xml

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<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_files</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>
                <refpurpose>Open the system journal for reading</refpurpose>
        </refnamediv>

        <refsynopsisdiv>
                <funcsynopsis>
                        <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</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_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>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, but it must be passed as 0 as no flags
                are currently understood for this call.</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><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>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-journal</constant> <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
                file.</para>
        </refsect1>

        <refsect1>
                <title>History</title>

                <para><function>sd_journal_open()</function>,
                <function>sd_journal_close()</function>,
                <constant>SD_JOURNAL_LOCAL_ONLY</constant>,
                <constant>SD_JOURNAL_RUNTIME_ONLY</constant>,
                <constant>SD_JOURNAL_SYSTEM_ONLY</constant> were added
                in systemd-38.</para>

                <para><function>sd_journal_open_directory()</function>
                was added in systemd-187.</para>

                <para><constant>SD_JOURNAL_SYSTEM</constant>,
                <constant>SD_JOURNAL_CURRENT_USER</constant>,
                and <function>sd_journal_open_files()</function>
                were added in systemd-205.
                <constant>SD_JOURNAL_SYSTEM_ONLY</constant>
                was deprecated.</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>
                </para>
        </refsect1>

</refentry>