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>