man/sd_journal_stream_fd.xml

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   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4
   5 <!--
   6   SPDX-License-Identifier: LGPL-2.1+
   7
   8   This file is part of systemd.
   9
  10   Copyright 2012 Lennart Poettering
  11 -->
  12
  13 <refentry id="sd_journal_stream_fd">
  14
  15   <refentryinfo>
  16     <title>sd_journal_stream_fd</title>
  17     <productname>systemd</productname>
  18
  19     <authorgroup>
  20       <author>
  21         <contrib>Developer</contrib>
  22         <firstname>Lennart</firstname>
  23         <surname>Poettering</surname>
  24         <email>lennart@poettering.net</email>
  25       </author>
  26     </authorgroup>
  27   </refentryinfo>
  28
  29   <refmeta>
  30     <refentrytitle>sd_journal_stream_fd</refentrytitle>
  31     <manvolnum>3</manvolnum>
  32   </refmeta>
  33
  34   <refnamediv>
  35     <refname>sd_journal_stream_fd</refname>
  36     <refpurpose>Create log stream file descriptor to the journal</refpurpose>
  37   </refnamediv>
  38
  39   <refsynopsisdiv>
  40     <funcsynopsis>
  41       <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>
  42
  43       <funcprototype>
  44         <funcdef>int <function>sd_journal_stream_fd</function></funcdef>
  45         <paramdef>const char *<parameter>identifier</parameter></paramdef>
  46         <paramdef>int <parameter>priority</parameter></paramdef>
  47         <paramdef>int <parameter>level_prefix</parameter></paramdef>
  48       </funcprototype>
  49
  50     </funcsynopsis>
  51   </refsynopsisdiv>
  52
  53   <refsect1>
  54     <title>Description</title>
  55
  56     <para><function>sd_journal_stream_fd()</function> may be used to
  57     create a log stream file descriptor. Log messages written to this
  58     file descriptor as simple newline-separated text strings are
  59     written to the journal. This file descriptor can be used
  60     internally by applications or be made standard output or standard
  61     error of other processes executed.</para>
  62
  63     <para><function>sd_journal_stream_fd()</function> takes a short
  64     program identifier string as first argument, which will be written
  65     to the journal as _SYSLOG_IDENTIFIER= field for each log entry
  66     (see
  67     <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>
  68     for more information). The second argument shall be the default
  69     priority level for all messages. The priority level is one of
  70     <constant>LOG_EMERG</constant>, <constant>LOG_ALERT</constant>,
  71     <constant>LOG_CRIT</constant>, <constant>LOG_ERR</constant>,
  72     <constant>LOG_WARNING</constant>, <constant>LOG_NOTICE</constant>,
  73     <constant>LOG_INFO</constant>, <constant>LOG_DEBUG</constant>, as
  74     defined in <filename>syslog.h</filename>, see
  75     <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  76     for details. The third argument is a boolean: if true kernel-style
  77     log level prefixes (such as <constant>SD_WARNING</constant>) are
  78     interpreted, see
  79     <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  80     for more information.</para>
  81
  82     <para>It is recommended that applications log UTF-8 messages only
  83     with this API, but this is not enforced.</para>
  84
  85     <para>Each invocation of <function>sd_journal_stream_fd()</function> allocates a new log stream file descriptor,
  86     that is not shared with prior or later invocations. The file descriptor is write-only (its reading direction is
  87     shut down), and <constant>O_NONBLOCK</constant> is turned off initially.</para>
  88   </refsect1>
  89
  90   <refsect1>
  91     <title>Return Value</title>
  92
  93     <para>The call returns a valid write-only file descriptor on
  94     success or a negative errno-style error code.</para>
  95   </refsect1>
  96
  97   <refsect1>
  98     <title>Signal safety</title>
  99
 100     <para><function>sd_journal_stream_fd()</function> is "async signal safe" in the meaning of <citerefentry
 101     project='man-pages'><refentrytitle>signal-safety</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 102     </para>
 103   </refsect1>
 104
 105   <refsect1>
 106     <title>Notes</title>
 107
 108     <para>Function <function>sd_journal_stream_fd()</function> is thread-safe and may be called
 109     from multiple threads.</para>
 110
 111     <para>The <function>sd_journal_stream_fd()</function> interface is
 112     available as a shared library, which can be compiled and linked to
 113     with the
 114     <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 115     file.</para>
 116   </refsect1>
 117
 118   <refsect1>
 119     <title>Examples</title>
 120
 121     <para>Creating a log stream suitable for
 122     <citerefentry project='man-pages'><refentrytitle>fprintf</refentrytitle><manvolnum>3</manvolnum></citerefentry>:</para>
 123
 124     <programlisting>#include &lt;syslog.h&gt;
 125 #include &lt;stdio.h&gt;
 126 #include &lt;string.h&gt;
 127 #include &lt;unistd.h&gt;
 128 #include &lt;systemd/sd-journal.h&gt;
 129 #include &lt;systemd/sd-daemon.h&gt;
 130
 131 int main(int argc, char *argv[]) {
 132   int fd;
 133   FILE *log;
 134   fd = sd_journal_stream_fd("test", LOG_INFO, 1);
 135   if (fd &lt; 0) {
 136     fprintf(stderr, "Failed to create stream fd: %s\n", strerror(-fd));
 137     return 1;
 138   }
 139   log = fdopen(fd, "w");
 140   if (!log) {
 141     fprintf(stderr, "Failed to create file object: %m\n");
 142     close(fd);
 143     return 1;
 144   }
 145   fprintf(log, "Hello World!\n");
 146   fprintf(log, SD_WARNING "This is a warning!\n");
 147   fclose(log);
 148   return 0;
 149 }</programlisting>
 150
 151   </refsect1>
 152
 153   <refsect1>
 154     <title>See Also</title>
 155
 156     <para>
 157       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 158       <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 159       <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 160       <citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 161       <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 162       <citerefentry project='man-pages'><refentrytitle>fprintf</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 163       <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 164     </para>
 165   </refsect1>
 166
 167 </refentry>