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
  68                 be used to create a log stream file descriptor. Log
  69                 messages written to this file descriptor as simple
  70                 newline separated text strings are written to the
  71                 journal. This file descriptor can be used internally
  72                 by applications or be made STDOUT/STDERR of other
  73                 processes executed.</para>
  74
  75                 <para><function>sd_journal_stream_fd()</function>
  76                 takes a short program identifier string as first
  77                 argument, which will be written to the journal as
  78                 _SYSLOG_IDENTIFIER= field for each log entry (see
  79                 <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>
  80                 for more information). The second argument shall be
  81                 the default priority level for all messages. The
  82                 priority level is one of <constant>LOG_EMERG</constant>,
  83                 <constant>LOG_ALERT</constant>,
  84                 <constant>LOG_CRIT</constant>,
  85                 <constant>LOG_ERR</constant>,
  86                 <constant>LOG_WARNING</constant>,
  87                 <constant>LOG_NOTICE</constant>,
  88                 <constant>LOG_INFO</constant>,
  89                 <constant>LOG_DEBUG</constant>, as defined in
  90                 <filename>syslog.h</filename>, see
  91                 <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  92                 for details. The third argument is a boolean: if true
  93                 kernel-style log priority level prefixes (such as
  94                 <constant>SD_WARNING</constant>) are interpreted, see
  95                 <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  96                 for more information.</para>
  97
  98                 <para>It is recommended that applications log UTF-8
  99                 messages only with this API, but this is not
 100                 enforced.</para>
 101
 102         </refsect1>
 103
 104         <refsect1>
 105                 <title>Return Value</title>
 106
 107                 <para>The call returns a valid write-only file descriptor on success or a
 108                 negative errno-style error code.</para>
 109         </refsect1>
 110
 111         <refsect1>
 112                 <title>Notes</title>
 113
 114                 <para>The <function>sd_journal_stream_fd()</function>
 115                 interface is available as shared library, which can
 116                 be compiled and linked to with the
 117                 <constant>libsystemd-journal</constant> <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 118                 file.</para>
 119         </refsect1>
 120
 121         <refsect1>
 122                 <title>Examples</title>
 123
 124                 <para>Creating a log stream suitable for
 125                 <citerefentry><refentrytitle>fprintf</refentrytitle><manvolnum>3</manvolnum></citerefentry>:</para>
 126
 127                 <programlisting>#include &lt;syslog.h&gt;
 128 #include &lt;stdio.h&gt;
 129 #include &lt;string.h&gt;
 130 #include &lt;unistd.h&gt;
 131 #include &lt;systemd/sd-journal.h&gt;
 132 #include &lt;systemd/sd-daemon.h&gt;
 133
 134 int main(int argc, char *argv[]) {
 135         int fd;
 136         FILE *log;
 137         fd = sd_journal_stream_fd("test", LOG_INFO, 1);
 138         if (fd &lt; 0) {
 139                 fprintf(stderr, "Failed to create stream fd: %s\n", strerror(-fd));
 140                 return 1;
 141         }
 142         log = fdopen(fd, "w");
 143         if (!log) {
 144                 fprintf(stderr, "Failed to create file object: %m\n");
 145                 close(fd);
 146                 return 1;
 147         }
 148         fprintf(log, "Hello World!\n");
 149         fprintf(log, SD_WARNING "This is a warning!\n");
 150         fclose(log);
 151         return 0;
 152 }</programlisting>
 153
 154         </refsect1>
 155
 156         <refsect1>
 157                 <title>See Also</title>
 158
 159                 <para>
 160                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 161                         <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 162                         <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 163                         <citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 164                         <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 165                         <citerefentry><refentrytitle>fprintf</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 166                         <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 167                 </para>
 168         </refsect1>
 169
 170 </refentry>