man/sd_journal_stream_fd.xml

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