man/sd_journal_print.xml

   1 <?xml version='1.0'?> <!--*-nxml-*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4 <!-- SPDX-License-Identifier: LGPL-2.1+ -->
   5
   6 <refentry id="sd_journal_print" xmlns:xi="http://www.w3.org/2001/XInclude">
   7
   8   <refentryinfo>
   9     <title>sd_journal_print</title>
  10     <productname>systemd</productname>
  11   </refentryinfo>
  12
  13   <refmeta>
  14     <refentrytitle>sd_journal_print</refentrytitle>
  15     <manvolnum>3</manvolnum>
  16   </refmeta>
  17
  18   <refnamediv>
  19     <refname>sd_journal_print</refname>
  20     <refname>sd_journal_printv</refname>
  21     <refname>sd_journal_send</refname>
  22     <refname>sd_journal_sendv</refname>
  23     <refname>sd_journal_perror</refname>
  24     <refname>SD_JOURNAL_SUPPRESS_LOCATION</refname>
  25     <refpurpose>Submit log entries to the journal</refpurpose>
  26   </refnamediv>
  27
  28   <refsynopsisdiv>
  29     <funcsynopsis>
  30       <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>
  31
  32       <funcprototype>
  33         <funcdef>int <function>sd_journal_print</function></funcdef>
  34         <paramdef>int <parameter>priority</parameter></paramdef>
  35         <paramdef>const char *<parameter>format</parameter></paramdef>
  36         <paramdef>…</paramdef>
  37       </funcprototype>
  38
  39       <funcprototype>
  40         <funcdef>int <function>sd_journal_printv</function></funcdef>
  41         <paramdef>int <parameter>priority</parameter></paramdef>
  42         <paramdef>const char *<parameter>format</parameter></paramdef>
  43         <paramdef>va_list <parameter>ap</parameter></paramdef>
  44       </funcprototype>
  45
  46       <funcprototype>
  47         <funcdef>int <function>sd_journal_send</function></funcdef>
  48         <paramdef>const char *<parameter>format</parameter></paramdef>
  49         <paramdef>…</paramdef>
  50       </funcprototype>
  51
  52       <funcprototype>
  53         <funcdef>int <function>sd_journal_sendv</function></funcdef>
  54         <paramdef>const struct iovec *<parameter>iov</parameter></paramdef>
  55         <paramdef>int <parameter>n</parameter></paramdef>
  56       </funcprototype>
  57
  58       <funcprototype>
  59         <funcdef>int <function>sd_journal_perror</function></funcdef>
  60         <paramdef>const char *<parameter>message</parameter></paramdef>
  61       </funcprototype>
  62
  63     </funcsynopsis>
  64   </refsynopsisdiv>
  65
  66   <refsect1>
  67     <title>Description</title>
  68
  69     <para><function>sd_journal_print()</function> may be used to submit simple, plain text log entries to the system
  70     journal. The first argument is a priority value. This is followed by a format string and its parameters, similar to
  71     <citerefentry project='man-pages'><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry> or
  72     <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
  73     The priority value is one of <constant>LOG_EMERG</constant>, <constant>LOG_ALERT</constant>,
  74     <constant>LOG_CRIT</constant>, <constant>LOG_ERR</constant>, <constant>LOG_WARNING</constant>,
  75     <constant>LOG_NOTICE</constant>, <constant>LOG_INFO</constant>, <constant>LOG_DEBUG</constant>, as defined in
  76     <filename>syslog.h</filename>, see <citerefentry
  77     project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry> for details. It is
  78     recommended to use this call to submit log messages in the application locale or system locale and in UTF-8 format,
  79     but no such restrictions are enforced. Note that log messages written using this function are generally not
  80     expected to end in a new-line character. However, as all trailing whitespace (including spaces, new-lines,
  81     tabulators and carriage returns) are automatically stripped from the logged string, it is acceptable to specify one
  82     (or more). Empty lines (after trailing whitespace removal) are suppressed. On non-empty lines, leading whitespace
  83     (as well as inner whitespace) is left unmodified. </para>
  84
  85     <para><function>sd_journal_printv()</function> is similar to
  86     <function>sd_journal_print()</function> but takes a variable
  87     argument list encapsulated in an object of type
  88     <varname>va_list</varname> (see
  89     <citerefentry project='man-pages'><refentrytitle>stdarg</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  90     for more information) instead of the format string. It is
  91     otherwise equivalent in behavior.</para>
  92
  93     <para><function>sd_journal_send()</function> may be used to submit structured log entries to the system journal. It
  94     takes a series of format strings, each immediately followed by their associated parameters, terminated by
  95     <constant>NULL</constant>. The strings passed should be of the format <literal>VARIABLE=value</literal>.  The
  96     variable name must be in uppercase and consist only of characters, numbers and underscores, and may not begin with
  97     an underscore. (All assignments that do not follow this syntax will be ignored.) The value can be of any size and
  98     format. It is highly recommended to submit text strings formatted in the UTF-8 character encoding only, and submit
  99     binary fields only when formatting in UTF-8 strings is not sensible. A number of well-known fields are defined, see
 100     <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
 101     details, but additional application defined fields may be used. A variable may be assigned more than one value per
 102     entry. If this function is used, trailing whitespace is automatically removed from each formatted field.</para>
 103
 104     <para><function>sd_journal_sendv()</function> is similar to <function>sd_journal_send()</function> but takes an
 105     array of <varname>struct iovec</varname> (as defined in <filename>uio.h</filename>, see <citerefentry
 106     project='man-pages'><refentrytitle>readv</refentrytitle><manvolnum>3</manvolnum></citerefentry> for details)
 107     instead of the format string. Each structure should reference one field of the entry to submit. The second argument
 108     specifies the number of structures in the array.  <function>sd_journal_sendv()</function> is particularly useful to
 109     submit binary objects to the journal where that is necessary. Note that this function will not strip trailing
 110     whitespace of the passed fields, but passes the specified data along unmodified. This is different from both
 111     <function>sd_journal_print()</function> and <function>sd_journal_send()</function> described above, which are based
 112     on format strings, and do strip trailing whitespace.</para>
 113
 114     <para><function>sd_journal_perror()</function> is a similar to
 115     <citerefentry project='die-net'><refentrytitle>perror</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 116     and writes a message to the journal that consists of the passed
 117     string, suffixed with ": " and a human-readable representation of
 118     the current error code stored in
 119     <citerefentry project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 120     If the message string is passed as <constant>NULL</constant> or
 121     empty string, only the error string representation will be
 122     written, prefixed with nothing. An additional journal field ERRNO=
 123     is included in the entry containing the numeric error code
 124     formatted as decimal string. The log priority used is
 125     <constant>LOG_ERR</constant> (3).</para>
 126
 127     <para>Note that <function>sd_journal_send()</function> is a
 128     wrapper around <function>sd_journal_sendv()</function> to make it
 129     easier to use when only text strings shall be submitted. Also, the
 130     following two calls are mostly equivalent:</para>
 131
 132     <programlisting>sd_journal_print(LOG_INFO, "Hello World, this is PID %lu!", (unsigned long) getpid());
 133
 134 sd_journal_send("MESSAGE=Hello World, this is PID %lu!", (unsigned long) getpid(),
 135                 "PRIORITY=%i", LOG_INFO,
 136                 NULL);</programlisting>
 137
 138     <para>Note that these calls implicitly add fields for the source
 139     file, function name and code line where invoked. This is
 140     implemented with macros. If this is not desired, it can be turned
 141     off by defining SD_JOURNAL_SUPPRESS_LOCATION before including
 142     <filename>sd-journal.h</filename>.</para>
 143
 144     <para><citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 145     and <function>sd_journal_print()</function> may
 146     largely be used interchangeably
 147     functionality-wise. However, note that log messages
 148     logged via the former take a different path to the
 149     journal server than the later, and hence global
 150     chronological ordering between the two streams cannot
 151     be guaranteed. Using
 152     <function>sd_journal_print()</function> has the
 153     benefit of logging source code line, filenames, and
 154     functions as metadata along all entries, and
 155     guaranteeing chronological ordering with structured
 156     log entries that are generated via
 157     <function>sd_journal_send()</function>. Using
 158     <function>syslog()</function> has the benefit of being
 159     more portable.</para>
 160   </refsect1>
 161
 162   <refsect1>
 163     <title>Return Value</title>
 164
 165     <para>The five calls return 0 on success or a negative errno-style error code. The <citerefentry
 166     project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry> variable itself is
 167     not altered.</para>
 168
 169     <para>If
 170     <citerefentry><refentrytitle>systemd-journald</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 171     is not running (the socket is not present), those functions do
 172     nothing, and also return 0.</para>
 173   </refsect1>
 174
 175   <refsect1>
 176     <title>Thread safety</title>
 177
 178     <xi:include href="threads-aware.xml" xpointer="safe"/>
 179
 180     <para><function>sd_journal_sendv()</function> is "async signal safe" in the meaning of <citerefentry
 181     project='man-pages'><refentrytitle>signal-safety</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 182     </para>
 183
 184     <para><function>sd_journal_print</function>,
 185     <function>sd_journal_printv</function>,
 186     <function>sd_journal_send</function>, and
 187     <function>sd_journal_perror</function> are
 188     not async signal safe.</para>
 189   </refsect1>
 190
 191   <xi:include href="libsystemd-pkgconfig.xml" />
 192
 193   <refsect1>
 194     <title>See Also</title>
 195
 196     <para>
 197       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 198       <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 199       <citerefentry><refentrytitle>sd_journal_stream_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 200       <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 201       <citerefentry project='die-net'><refentrytitle>perror</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 202       <citerefentry project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 203       <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 204       <citerefentry project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 205       <citerefentry project='man-pages'><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 206     </para>
 207   </refsect1>
 208
 209 </refentry>