systemd/man/sd_journal_stream_fd.xml

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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
        "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

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<refentry id="sd_journal_stream_fd">

        <refentryinfo>
                <title>sd_journal_stream_fd</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_stream_fd</refentrytitle>
                <manvolnum>3</manvolnum>
        </refmeta>

        <refnamediv>
                <refname>sd_journal_stream_fd</refname>
                <refpurpose>Create log stream file descriptor to the journal</refpurpose>
        </refnamediv>

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

                        <funcprototype>
                                <funcdef>int <function>sd_journal_stream_fd</function></funcdef>
                                <paramdef>const char* <parameter>identifier</parameter></paramdef>
                                <paramdef>int <parameter>priority</parameter></paramdef>
                                <paramdef>int <parameter>level_prefix</parameter></paramdef>
                        </funcprototype>

                </funcsynopsis>
        </refsynopsisdiv>

        <refsect1>
                <title>Description</title>

                <para><function>sd_journal_stream_fd()</function> may
                be used to create a log stream file descriptor. Log
                messages written to this file descriptor as simple
                newline separated text strings are written to the
                journal. This file descriptor can be used internally
                by applications or be made STDOUT/STDERR of other
                processes executed.</para>

                <para><function>sd_journal_stream_fd()</function>
                takes a short program identifier string as first
                argument, which will be written to the journal as
                _SYSLOG_IDENTIFIER= field for each log entry (see
                <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>
                for more information). The second argument shall be
                the default priority level for all messages. The
                priority level 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. The third argument is a boolean: if true
                kernel-style log priority level prefixes (such as
                <constant>SD_WARNING</constant>) are interpreted, see
                <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                for more information.</para>

                <para>It is recommended that applications log UTF-8
                messages only with this API, but this is not
                enforced.</para>

        </refsect1>

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

                <para>The call returns a valid write-only file descriptor on success or a
                negative errno-style error code.</para>
        </refsect1>

        <refsect1>
                <title>Notes</title>

                <para>The <function>sd_journal_stream_fd()</function>
                interface is available as 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>Examples</title>

                <para>Creating a log stream suitable for
                <citerefentry><refentrytitle>fprintf</refentrytitle><manvolnum>3</manvolnum></citerefentry>:</para>

                <programlisting>#include &lt;syslog.h&gt;
#include &lt;stdio.h&gt;
#include &lt;string.h&gt;
#include &lt;unistd.h&gt;
#include &lt;systemd/sd-journal.h&gt;
#include &lt;systemd/sd-daemon.h&gt;

int main(int argc, char *argv[]) {
        int fd;
        FILE *log;
        fd = sd_journal_stream_fd("test", LOG_INFO, 1);
        if (fd &lt; 0) {
                fprintf(stderr, "Failed to create stream fd: %s\n", strerror(-fd));
                return 1;
        }
        log = fdopen(fd, "w");
        if (!log) {
                fprintf(stderr, "Failed to create file object: %m\n");
                close(fd);
                return 1;
        }
        fprintf(log, "Hello World!\n");
        fprintf(log, SD_WARNING "This is a warning!\n");
        fclose(log);
        return 0;
}</programlisting>

        </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-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>fprintf</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>
                </para>
        </refsect1>

</refentry>