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
  98     <para>Each invocation of <function>sd_journal_stream_fd()</function> allocates a new log stream file descriptor,
  99     that is not shared with prior or later invocations. The file descriptor is write-only (its reading direction is
 100     shut down), and <constant>O_NONBLOCK</constant> is turned off initially.</para>
 101   </refsect1>
 102
 103   <refsect1>
 104     <title>Return Value</title>
 105
 106     <para>The call returns a valid write-only file descriptor on
 107     success or a negative errno-style error code.</para>
 108   </refsect1>
 109
 110   <refsect1>
 111     <title>Signal safety</title>
 112
 113     <para><function>sd_journal_stream_fd()</function> is "async signal safe" in the meaning of <citerefentry
 114     project='man-pages'><refentrytitle>signal-safety</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 115     </para>
 116   </refsect1>
 117
 118   <refsect1>
 119     <title>Notes</title>
 120
 121     <para>Function <function>sd_journal_stream_fd()</function> is thread-safe and may be called
 122     from multiple threads.</para>
 123
 124     <para>The <function>sd_journal_stream_fd()</function> interface is
 125     available as a shared library, which can be compiled and linked to
 126     with the
 127     <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 128     file.</para>
 129   </refsect1>
 130
 131   <refsect1>
 132     <title>Examples</title>
 133
 134     <para>Creating a log stream suitable for
 135     <citerefentry project='man-pages'><refentrytitle>fprintf</refentrytitle><manvolnum>3</manvolnum></citerefentry>:</para>
 136
 137     <programlisting>#include &lt;syslog.h&gt;
 138 #include &lt;stdio.h&gt;
 139 #include &lt;string.h&gt;
 140 #include &lt;unistd.h&gt;
 141 #include &lt;systemd/sd-journal.h&gt;
 142 #include &lt;systemd/sd-daemon.h&gt;
 143
 144 int main(int argc, char *argv[]) {
 145   int fd;
 146   FILE *log;
 147   fd = sd_journal_stream_fd("test", LOG_INFO, 1);
 148   if (fd &lt; 0) {
 149     fprintf(stderr, "Failed to create stream fd: %s\n", strerror(-fd));
 150     return 1;
 151   }
 152   log = fdopen(fd, "w");
 153   if (!log) {
 154     fprintf(stderr, "Failed to create file object: %m\n");
 155     close(fd);
 156     return 1;
 157   }
 158   fprintf(log, "Hello World!\n");
 159   fprintf(log, SD_WARNING "This is a warning!\n");
 160   fclose(log);
 161   return 0;
 162 }</programlisting>
 163
 164   </refsect1>
 165
 166   <refsect1>
 167     <title>See Also</title>
 168
 169     <para>
 170       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 171       <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 172       <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 173       <citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 174       <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 175       <citerefentry project='man-pages'><refentrytitle>fprintf</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 176       <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 177     </para>
 178   </refsect1>
 179
 180 </refentry>