man/sd_journal_print.xml

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<refentry id="sd_journal_print">

  <refentryinfo>
    <title>sd_journal_print</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_print</refentrytitle>
    <manvolnum>3</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>sd_journal_print</refname>
    <refname>sd_journal_printv</refname>
    <refname>sd_journal_send</refname>
    <refname>sd_journal_sendv</refname>
    <refname>sd_journal_perror</refname>
    <refname>SD_JOURNAL_SUPPRESS_LOCATION</refname>
    <refpurpose>Submit log entries to the journal</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <funcsynopsis>
      <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>

      <funcprototype>
        <funcdef>int <function>sd_journal_print</function></funcdef>
        <paramdef>int <parameter>priority</parameter></paramdef>
        <paramdef>const char *<parameter>format</parameter></paramdef>
        <paramdef>...</paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_journal_printv</function></funcdef>
        <paramdef>int <parameter>priority</parameter></paramdef>
        <paramdef>const char *<parameter>format</parameter></paramdef>
        <paramdef>va_list <parameter>ap</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_journal_send</function></funcdef>
        <paramdef>const char *<parameter>format</parameter></paramdef>
        <paramdef>...</paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_journal_sendv</function></funcdef>
        <paramdef>const struct iovec *<parameter>iov</parameter></paramdef>
        <paramdef>int <parameter>n</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_journal_perror</function></funcdef>
        <paramdef>const char *<parameter>message</parameter></paramdef>
      </funcprototype>

    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><function>sd_journal_print()</function> may be used to
    submit simple, plain text log entries to the system journal. The
    first argument is a priority value. This is followed by a format
    string and its parameters, similar to
    <citerefentry project='man-pages'><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    or
    <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
    The priority value is one of
    <constant>LOG_EMERG</constant>,
    <constant>LOG_ALERT</constant>,
    <constant>LOG_CRIT</constant>,
    <constant>LOG_ERR</constant>,
    <constant>LOG_WARNING</constant>,
    <constant>LOG_NOTICE</constant>,
    <constant>LOG_INFO</constant>,
    <constant>LOG_DEBUG</constant>, as defined in
    <filename>syslog.h</filename>, see
    <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    for details. It is recommended to use this call to submit log
    messages in the application locale or system locale and in UTF-8
    format, but no such restrictions are enforced.</para>

    <para><function>sd_journal_printv()</function> is similar to
    <function>sd_journal_print()</function> but takes a variable
    argument list encapsulated in an object of type
    <varname>va_list</varname> (see
    <citerefentry project='man-pages'><refentrytitle>stdarg</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    for more information) instead of the format string. It is
    otherwise equivalent in behavior.</para>

    <para><function>sd_journal_send()</function> may be used to submit
    structured log entries to the system journal. It takes a series of
    format strings, each immediately followed by their associated
    parameters, terminated by <constant>NULL</constant>. The strings
    passed should be of the format <literal>VARIABLE=value</literal>.
    The variable name must be in uppercase and consist only of
    characters, numbers and underscores, and may not begin with an
    underscore. (All assignments that do not follow this syntax will
    be ignored.) The value can be of any size and format. It is highly
    recommended to submit text strings formatted in the UTF-8
    character encoding only, and submit binary fields only when
    formatting in UTF-8 strings is not sensible. A number of
    well-known fields are defined, see
    <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>
    for details, but additional application defined fields may be
    used. A variable may be assigned more than one value per
    entry.</para>

    <para><function>sd_journal_sendv()</function> is similar to
    <function>sd_journal_send()</function> but takes an array of
    <varname>struct iovec</varname> (as defined in
    <filename>uio.h</filename>, see
    <citerefentry project='man-pages'><refentrytitle>readv</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    for details) instead of the format string. Each structure should
    reference one field of the entry to submit. The second argument
    specifies the number of structures in the array.
    <function>sd_journal_sendv()</function> is particularly useful to
    submit binary objects to the journal where that is
    necessary.</para>

    <para><function>sd_journal_perror()</function> is a similar to
    <citerefentry project='die-net'><refentrytitle>perror</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    and writes a message to the journal that consists of the passed
    string, suffixed with ": " and a human-readable representation of
    the current error code stored in
    <citerefentry project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
    If the message string is passed as <constant>NULL</constant> or
    empty string, only the error string representation will be
    written, prefixed with nothing. An additional journal field ERRNO=
    is included in the entry containing the numeric error code
    formatted as decimal string. The log priority used is
    <constant>LOG_ERR</constant> (3).</para>

    <para>Note that <function>sd_journal_send()</function> is a
    wrapper around <function>sd_journal_sendv()</function> to make it
    easier to use when only text strings shall be submitted. Also, the
    following two calls are mostly equivalent:</para>

    <programlisting>sd_journal_print(LOG_INFO, "Hello World, this is PID %lu!", (unsigned long) getpid());

sd_journal_send("MESSAGE=Hello World, this is PID %lu!", (unsigned long) getpid(),
    "PRIORITY=%i", LOG_INFO,
    NULL);</programlisting>

    <para>Note that these calls implicitly add fields for the source
    file, function name and code line where invoked. This is
    implemented with macros. If this is not desired, it can be turned
    off by defining SD_JOURNAL_SUPPRESS_LOCATION before including
    <filename>sd-journal.h</filename>.</para>

    <para><citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    and <function>sd_journal_print()</function> may
    largely be used interchangeably
    functionality-wise. However, note that log messages
    logged via the former take a different path to the
    journal server than the later, and hence global
    chronological ordering between the two streams cannot
    be guaranteed. Using
    <function>sd_journal_print()</function> has the
    benefit of logging source code line, filenames, and
    functions as metadata along all entries, and
    guaranteeing chronological ordering with structured
    log entries that are generated via
    <function>sd_journal_send()</function>. Using
    <function>syslog()</function> has the benefit of being
    more portable.</para>
  </refsect1>

  <refsect1>
    <title>Return Value</title>

    <para>The four calls return 0 on success or a negative errno-style
    error code. The
    <citerefentry project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    variable itself is not altered.</para>

    <para>If
    <citerefentry><refentrytitle>systemd-journald</refentrytitle><manvolnum>8</manvolnum></citerefentry>
    is not running (the socket is not present), those functions do
    nothing, and also return 0.</para>
  </refsect1>

  <refsect1>
    <title>Async signal safety</title>
    <para><function>sd_journal_sendv()</function> is "async signal
    safe" in the meaning of
    <citerefentry project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
    </para>

    <para><function>sd_journal_print</function>,
    <function>sd_journal_printv</function>,
    <function>sd_journal_send</function>, and
    <function>sd_journal_perror</function> are
    not async signal safe.</para>
  </refsect1>

  <refsect1>
    <title>Notes</title>

    <para>The <function>sd_journal_print()</function>,
    <function>sd_journal_printv()</function>,
    <function>sd_journal_send()</function> and
    <function>sd_journal_sendv()</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_stream_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry project='die-net'><refentrytitle>perror</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
      <citerefentry project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
      <citerefentry project='man-pages'><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>