<?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>