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><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                or
                <citerefentry><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><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><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><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><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><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><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><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><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><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><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>perror</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry>
                </para>
        </refsect1>

</refentry>