sd_journal_print.xml 11 KB
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<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
        "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

<!--
  This file is part of systemd.

  Copyright 2012 Lennart Poettering

  systemd is free software; you can redistribute it and/or modify it
  under the terms of the GNU Lesser General Public License as published by
  the Free Software Foundation; either version 2.1 of the License, or
  (at your option) any later version.

  systemd is distributed in the hope that it will be useful, but
  WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public License
  along with systemd; If not, see <http://www.gnu.org/licenses/>.
-->

<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>
                <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>

                </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
                <literal>LOG_EMERG</literal>,
                <literal>LOG_ALERT</literal>,
                <literal>LOG_CRIT</literal>,
                <literal>LOG_ERR</literal>,
                <literal>LOG_WARNING</literal>,
                <literal>LOG_NOTICE</literal>,
                <literal>LOG_INFO</literal>,
                <literal>LOG_DEBUG</literal>, 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 <literal>va_list</literal> (see
                <citerefentry><refentrytitle>stdarg</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                for more information) instead of the format string. It
                is otherwise equivalent in behaviour.</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 a NULL. 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. 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.</para>

                <para><function>sd_journal_sendv()</function> is
                similar to <function>sd_journal_send()</function> but
                takes an array of <literal>struct iovec</literal> (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>Note that <function>sd_journal_send()</function>
                is a wapper 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>
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                <para><citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                and and <function>sd_journal_print()</function> may
                mostly be used interchangably
                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, file names, and
                functions as meta data 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>
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        </refsect1>

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

                <para>The four calls return 0 on success or a
                negative errno-style error code.</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 shared library, which can be compiled
                and linked to with the
                <literal>libsystemd-journal</literal>
                <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>,
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                        <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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                        <citerefentry><refentrytitle>sd_journal_stream_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>
                </para>
        </refsect1>

</refentry>