man/sd_journal_print.xml

   1 <?xml version='1.0'?> <!--*-nxml-*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3         "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4
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   8   Copyright 2012 Lennart Poettering
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  23
  24 <refentry id="sd_journal_print">
  25
  26         <refentryinfo>
  27                 <title>sd_journal_print</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_print</refentrytitle>
  42                 <manvolnum>3</manvolnum>
  43         </refmeta>
  44
  45         <refnamediv>
  46                 <refname>sd_journal_print</refname>
  47                 <refname>sd_journal_printv</refname>
  48                 <refname>sd_journal_send</refname>
  49                 <refname>sd_journal_sendv</refname>
  50                 <refpurpose>Submit log entries 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_print</function></funcdef>
  59                                 <paramdef>int <parameter>priority</parameter></paramdef>
  60                                 <paramdef>const char* <parameter>format</parameter></paramdef>
  61                                 <paramdef>...</paramdef>
  62                         </funcprototype>
  63
  64                         <funcprototype>
  65                                 <funcdef>int <function>sd_journal_printv</function></funcdef>
  66                                 <paramdef>int <parameter>priority</parameter></paramdef>
  67                                 <paramdef>const char* <parameter>format</parameter></paramdef>
  68                                 <paramdef>va_list <parameter>ap</parameter></paramdef>
  69                         </funcprototype>
  70
  71                         <funcprototype>
  72                                 <funcdef>int <function>sd_journal_send</function></funcdef>
  73                                 <paramdef>const char* <parameter>format</parameter></paramdef>
  74                                 <paramdef>...</paramdef>
  75                         </funcprototype>
  76
  77                         <funcprototype>
  78                                 <funcdef>int <function>sd_journal_sendv</function></funcdef>
  79                                 <paramdef>const struct iovec *<parameter>iov</parameter></paramdef>
  80                                 <paramdef>int <parameter>n</parameter></paramdef>
  81                         </funcprototype>
  82
  83                 </funcsynopsis>
  84         </refsynopsisdiv>
  85
  86         <refsect1>
  87                 <title>Description</title>
  88
  89                 <para><function>sd_journal_print()</function> may be
  90                 used to submit simple, plain text log entries to the
  91                 system journal. The first argument is a priority
  92                 value. This is followed by a format string and its
  93                 parameters, similar to
  94                 <citerefentry><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  95                 or
  96                 <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>. The
  97                 priority value is one of
  98                 <literal>LOG_EMERG</literal>,
  99                 <literal>LOG_ALERT</literal>,
 100                 <literal>LOG_CRIT</literal>,
 101                 <literal>LOG_ERR</literal>,
 102                 <literal>LOG_WARNING</literal>,
 103                 <literal>LOG_NOTICE</literal>,
 104                 <literal>LOG_INFO</literal>,
 105                 <literal>LOG_DEBUG</literal>, as defined in
 106                 <filename>syslog.h</filename>, see
 107                 <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 108                 for details. It is recommended to use this call to
 109                 submit log messages in the application locale or system
 110                 locale and in UTF-8 format, but no such restrictions
 111                 are enforced.</para>
 112
 113                 <para><function>sd_journal_printv()</function> is
 114                 similar to <function>sd_journal_print()</function> but
 115                 takes a variable argument list encapsulated in an
 116                 object of type <literal>va_list</literal> (see
 117                 <citerefentry><refentrytitle>stdarg</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 118                 for more information) instead of the format string. It
 119                 is otherwise equivalent in behaviour.</para>
 120
 121                 <para><function>sd_journal_send()</function> may be
 122                 used to submit structured log entries to the system
 123                 journal. It takes a series of format strings, each
 124                 immediately followed by their associated parameters,
 125                 terminated by a NULL. The strings passed should be of
 126                 the format <literal>VARIABLE=value</literal>. The
 127                 variable name must be in uppercase and consist only
 128                 of characters, numbers and underscores, and may not
 129                 begin with an underscore. The value can be of any size
 130                 and format. It is highly recommended to submit
 131                 text strings formatted in the UTF-8 character encoding
 132                 only, and submit binary fields only when formatting in
 133                 UTf-8 strings is not sensible. A number of well known
 134                 fields are defined, see
 135                 <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 136                 for details, but additional application defined fields
 137                 may be used.</para>
 138
 139                 <para><function>sd_journal_sendv()</function> is
 140                 similar to <function>sd_journal_send()</function> but
 141                 takes an array of <literal>struct iovec</literal> (as
 142                 defined in <filename>uio.h</filename>, see
 143                 <citerefentry><refentrytitle>readv</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 144                 for details) instead of the format string. Each
 145                 structure should reference one field of the entry to
 146                 submit. The second argument specifies the number of
 147                 structures in the
 148                 array. <function>sd_journal_sendv()</function> is
 149                 particularly useful to submit binary objects to the
 150                 journal where that is necessary.</para>
 151
 152                 <para>Note that <function>sd_journal_send()</function>
 153                 is a wapper around
 154                 <function>sd_journal_sendv()</function> to make it
 155                 easier to use when only text strings shall be
 156                 submitted. Also, the following two calls are
 157                 mostly equivalent:</para>
 158
 159                 <programlisting>sd_journal_print(LOG_INFO, "Hello World, this is PID %lu!", (unsigned long) getpid());
 160
 161 sd_journal_send("MESSAGE=Hello World, this is PID %lu!", (unsigned long) getpid(),
 162                 "PRIORITY=%i", LOG_INFO,
 163                 NULL);</programlisting>
 164
 165                 <para>Note that these calls implicitly add fields for
 166                 the source file, function name and code line where
 167                 invoked. This is implemented with macros. If this is
 168                 not desired it can be turned off by defining
 169                 SD_JOURNAL_SUPPRESS_LOCATION before including
 170                 <filename>sd-journal.h</filename>.</para>
 171
 172                 <para><citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 173                 and and <function>sd_journal_print()</function> may
 174                 mostly be used interchangably
 175                 functionality-wise. However, note that log messages
 176                 logged via the former take a different path to the
 177                 journal server than the later, and hence global
 178                 chronological ordering between the two streams cannot
 179                 be guaranteed. Using
 180                 <function>sd_journal_print()</function> has the
 181                 benefit of logging source code line, file names, and
 182                 functions as meta data along all entries, and
 183                 guaranteeing chronological ordering with structured
 184                 log entries that are generated via
 185                 <function>sd_journal_send()</function>. Using
 186                 <function>syslog()</function> has the benefit of being
 187                 more portable.</para>
 188         </refsect1>
 189
 190         <refsect1>
 191                 <title>Return Value</title>
 192
 193                 <para>The four calls return 0 on success or a
 194                 negative errno-style error code.</para>
 195         </refsect1>
 196
 197         <refsect1>
 198                 <title>Notes</title>
 199
 200                 <para>The <function>sd_journal_print()</function>,
 201                 <function>sd_journal_printv()</function>,
 202                 <function>sd_journal_send()</function> and
 203                 <function>sd_journal_sendv()</function> interfaces
 204                 are available as shared library, which can be compiled
 205                 and linked to with the
 206                 <literal>libsystemd-journal</literal>
 207                 <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 208                 file.</para>
 209         </refsect1>
 210
 211         <refsect1>
 212                 <title>See Also</title>
 213
 214                 <para>
 215                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 216                         <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 217                         <citerefentry><refentrytitle>sd_journal_stream_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 218                         <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 219                         <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 220                 </para>
 221         </refsect1>
 222
 223 </refentry>