man/sd_journal_stream_fd.xml

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