systemd/man/sd_journal_open.xml

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  Copyright 2012 Lennart Poettering

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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_open_container</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>int <function>sd_journal_open_container</function></funcdef>
        <paramdef>sd_journal **<parameter>ret</parameter></paramdef>
        <paramdef>const char *<parameter>machine</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><function>sd_journal_open_container()</function> is similar
    to <function>sd_journal_open()</function> but opens the journal
    files of a running OS container. The specified machine name refers
    to a container that is registered with
    <citerefentry><refentrytitle>systemd-machined</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</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</constant> <citerefentry project='die-net'><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>,
      <citerefentry><refentrytitle>systemd-machined</refentrytitle><manvolnum>8</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>