man/sd_journal_stream_fd.xml

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  10   Copyright 2012 Lennart Poettering
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  25
  26 <refentry id="sd_journal_stream_fd">
  27
  28   <refentryinfo>
  29     <title>sd_journal_stream_fd</title>
  30     <productname>systemd</productname>
  31
  32     <authorgroup>
  33       <author>
  34         <contrib>Developer</contrib>
  35         <firstname>Lennart</firstname>
  36         <surname>Poettering</surname>
  37         <email>lennart@poettering.net</email>
  38       </author>
  39     </authorgroup>
  40   </refentryinfo>
  41
  42   <refmeta>
  43     <refentrytitle>sd_journal_stream_fd</refentrytitle>
  44     <manvolnum>3</manvolnum>
  45   </refmeta>
  46
  47   <refnamediv>
  48     <refname>sd_journal_stream_fd</refname>
  49     <refpurpose>Create log stream file descriptor to the journal</refpurpose>
  50   </refnamediv>
  51
  52   <refsynopsisdiv>
  53     <funcsynopsis>
  54       <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>
  55
  56       <funcprototype>
  57         <funcdef>int <function>sd_journal_stream_fd</function></funcdef>
  58         <paramdef>const char *<parameter>identifier</parameter></paramdef>
  59         <paramdef>int <parameter>priority</parameter></paramdef>
  60         <paramdef>int <parameter>level_prefix</parameter></paramdef>
  61       </funcprototype>
  62
  63     </funcsynopsis>
  64   </refsynopsisdiv>
  65
  66   <refsect1>
  67     <title>Description</title>
  68
  69     <para><function>sd_journal_stream_fd()</function> may be used to
  70     create a log stream file descriptor. Log messages written to this
  71     file descriptor as simple newline-separated text strings are
  72     written to the journal. This file descriptor can be used
  73     internally by applications or be made standard output or standard
  74     error of other processes executed.</para>
  75
  76     <para><function>sd_journal_stream_fd()</function> takes a short
  77     program identifier string as first argument, which will be written
  78     to the journal as _SYSLOG_IDENTIFIER= field for each log entry
  79     (see
  80     <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>
  81     for more information). The second argument shall be the default
  82     priority level for all messages. The priority level is one of
  83     <constant>LOG_EMERG</constant>, <constant>LOG_ALERT</constant>,
  84     <constant>LOG_CRIT</constant>, <constant>LOG_ERR</constant>,
  85     <constant>LOG_WARNING</constant>, <constant>LOG_NOTICE</constant>,
  86     <constant>LOG_INFO</constant>, <constant>LOG_DEBUG</constant>, as
  87     defined in <filename>syslog.h</filename>, see
  88     <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  89     for details. The third argument is a boolean: if true kernel-style
  90     log level prefixes (such as <constant>SD_WARNING</constant>) are
  91     interpreted, see
  92     <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  93     for more information.</para>
  94
  95     <para>It is recommended that applications log UTF-8 messages only
  96     with this API, but this is not enforced.</para>
  97   </refsect1>
  98
  99   <refsect1>
 100     <title>Return Value</title>
 101
 102     <para>The call returns a valid write-only file descriptor on
 103     success or a negative errno-style error code.</para>
 104   </refsect1>
 105
 106   <refsect1>
 107     <title>Notes</title>
 108
 109     <para>Function <function>sd_journal_stream_fd()</function> is thread-safe and may be called
 110     from multiple threads. All calls will return the same file descriptor, although temporarily
 111     multiple file descriptors may be open.</para>
 112
 113     <para>The <function>sd_journal_stream_fd()</function> interface is
 114     available as a shared library, which can be compiled and linked to
 115     with the
 116     <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 117     file.</para>
 118   </refsect1>
 119
 120   <refsect1>
 121     <title>Examples</title>
 122
 123     <para>Creating a log stream suitable for
 124     <citerefentry project='man-pages'><refentrytitle>fprintf</refentrytitle><manvolnum>3</manvolnum></citerefentry>:</para>
 125
 126     <programlisting>#include &lt;syslog.h&gt;
 127 #include &lt;stdio.h&gt;
 128 #include &lt;string.h&gt;
 129 #include &lt;unistd.h&gt;
 130 #include &lt;systemd/sd-journal.h&gt;
 131 #include &lt;systemd/sd-daemon.h&gt;
 132
 133 int main(int argc, char *argv[]) {
 134   int fd;
 135   FILE *log;
 136   fd = sd_journal_stream_fd("test", LOG_INFO, 1);
 137   if (fd &lt; 0) {
 138     fprintf(stderr, "Failed to create stream fd: %s\n", strerror(-fd));
 139     return 1;
 140   }
 141   log = fdopen(fd, "w");
 142   if (!log) {
 143     fprintf(stderr, "Failed to create file object: %m\n");
 144     close(fd);
 145     return 1;
 146   }
 147   fprintf(log, "Hello World!\n");
 148   fprintf(log, SD_WARNING "This is a warning!\n");
 149   fclose(log);
 150   return 0;
 151 }</programlisting>
 152
 153   </refsect1>
 154
 155   <refsect1>
 156     <title>See Also</title>
 157
 158     <para>
 159       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 160       <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 161       <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 162       <citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 163       <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 164       <citerefentry project='man-pages'><refentrytitle>fprintf</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 165       <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 166     </para>
 167   </refsect1>
 168
 169 </refentry>