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<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
<refentry id="sd_journal_stream_fd" xmlns:xi="http://www.w3.org/2001/XInclude">
<refentryinfo>
<title>sd_journal_stream_fd</title>
<productname>systemd</productname>
</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 <systemd/sd-journal.h></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 standard output or standard
error 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 project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
for details. The third argument is a boolean: if true kernel-style
log 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>
<para>Each invocation of <function>sd_journal_stream_fd()</function> allocates a new log stream file descriptor,
that is not shared with prior or later invocations. The file descriptor is write-only (its reading direction is
shut down), and <constant>O_NONBLOCK</constant> is turned off initially.</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>Signal safety</title>
<para><function>sd_journal_stream_fd()</function> is "async signal safe" in the meaning of <citerefentry
project='man-pages'><refentrytitle>signal-safety</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
</para>
</refsect1>
<refsect1>
<title>Notes</title>
<xi:include href="threads-aware.xml" xpointer="safe"/>
<xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
</refsect1>
<refsect1>
<title>Examples</title>
<para>Creating a log stream suitable for
<citerefentry project='man-pages'><refentrytitle>fprintf</refentrytitle><manvolnum>3</manvolnum></citerefentry>:</para>
<programlisting>#include <syslog.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <systemd/sd-journal.h>
#include <systemd/sd-daemon.h>
int main(int argc, char *argv[]) {
int fd;
FILE *log;
fd = sd_journal_stream_fd("test", LOG_INFO, 1);
if (fd < 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 project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry project='man-pages'><refentrytitle>fprintf</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
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