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
   5 <!--
   6   SPDX-License-Identifier: LGPL-2.1+
   7 -->
   8
   9 <refentry id="sd_journal_print" xmlns:xi="http://www.w3.org/2001/XInclude">
  10
  11   <refentryinfo>
  12     <title>sd_journal_print</title>
  13     <productname>systemd</productname>
  14   </refentryinfo>
  15
  16   <refmeta>
  17     <refentrytitle>sd_journal_print</refentrytitle>
  18     <manvolnum>3</manvolnum>
  19   </refmeta>
  20
  21   <refnamediv>
  22     <refname>sd_journal_print</refname>
  23     <refname>sd_journal_printv</refname>
  24     <refname>sd_journal_send</refname>
  25     <refname>sd_journal_sendv</refname>
  26     <refname>sd_journal_perror</refname>
  27     <refname>SD_JOURNAL_SUPPRESS_LOCATION</refname>
  28     <refpurpose>Submit log entries to the journal</refpurpose>
  29   </refnamediv>
  30
  31   <refsynopsisdiv>
  32     <funcsynopsis>
  33       <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>
  34
  35       <funcprototype>
  36         <funcdef>int <function>sd_journal_print</function></funcdef>
  37         <paramdef>int <parameter>priority</parameter></paramdef>
  38         <paramdef>const char *<parameter>format</parameter></paramdef>
  39         <paramdef>…</paramdef>
  40       </funcprototype>
  41
  42       <funcprototype>
  43         <funcdef>int <function>sd_journal_printv</function></funcdef>
  44         <paramdef>int <parameter>priority</parameter></paramdef>
  45         <paramdef>const char *<parameter>format</parameter></paramdef>
  46         <paramdef>va_list <parameter>ap</parameter></paramdef>
  47       </funcprototype>
  48
  49       <funcprototype>
  50         <funcdef>int <function>sd_journal_send</function></funcdef>
  51         <paramdef>const char *<parameter>format</parameter></paramdef>
  52         <paramdef>…</paramdef>
  53       </funcprototype>
  54
  55       <funcprototype>
  56         <funcdef>int <function>sd_journal_sendv</function></funcdef>
  57         <paramdef>const struct iovec *<parameter>iov</parameter></paramdef>
  58         <paramdef>int <parameter>n</parameter></paramdef>
  59       </funcprototype>
  60
  61       <funcprototype>
  62         <funcdef>int <function>sd_journal_perror</function></funcdef>
  63         <paramdef>const char *<parameter>message</parameter></paramdef>
  64       </funcprototype>
  65
  66     </funcsynopsis>
  67   </refsynopsisdiv>
  68
  69   <refsect1>
  70     <title>Description</title>
  71
  72     <para><function>sd_journal_print()</function> may be used to submit simple, plain text log entries to the system
  73     journal. The first argument is a priority value. This is followed by a format string and its parameters, similar to
  74     <citerefentry project='man-pages'><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry> or
  75     <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
  76     The priority value is one of <constant>LOG_EMERG</constant>, <constant>LOG_ALERT</constant>,
  77     <constant>LOG_CRIT</constant>, <constant>LOG_ERR</constant>, <constant>LOG_WARNING</constant>,
  78     <constant>LOG_NOTICE</constant>, <constant>LOG_INFO</constant>, <constant>LOG_DEBUG</constant>, as defined in
  79     <filename>syslog.h</filename>, see <citerefentry
  80     project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry> for details. It is
  81     recommended to use this call to submit log messages in the application locale or system locale and in UTF-8 format,
  82     but no such restrictions are enforced. Note that log messages written using this function are generally not
  83     expected to end in a new-line character. However, as all trailing whitespace (including spaces, new-lines,
  84     tabulators and carriage returns) are automatically stripped from the logged string, it is acceptable to specify one
  85     (or more). Empty lines (after trailing whitespace removal) are suppressed. On non-empty lines, leading whitespace
  86     (as well as inner whitespace) is left unmodified. </para>
  87
  88     <para><function>sd_journal_printv()</function> is similar to
  89     <function>sd_journal_print()</function> but takes a variable
  90     argument list encapsulated in an object of type
  91     <varname>va_list</varname> (see
  92     <citerefentry project='man-pages'><refentrytitle>stdarg</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  93     for more information) instead of the format string. It is
  94     otherwise equivalent in behavior.</para>
  95
  96     <para><function>sd_journal_send()</function> may be used to submit structured log entries to the system journal. It
  97     takes a series of format strings, each immediately followed by their associated parameters, terminated by
  98     <constant>NULL</constant>. The strings passed should be of the format <literal>VARIABLE=value</literal>.  The
  99     variable name must be in uppercase and consist only of characters, numbers and underscores, and may not begin with
 100     an underscore. (All assignments that do not follow this syntax will be ignored.) The value can be of any size and
 101     format. It is highly recommended to submit text strings formatted in the UTF-8 character encoding only, and submit
 102     binary fields only when formatting in UTF-8 strings is not sensible. A number of well-known fields are defined, see
 103     <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
 104     details, but additional application defined fields may be used. A variable may be assigned more than one value per
 105     entry. If this function is used, trailing whitespace is automatically removed from each formatted field.</para>
 106
 107     <para><function>sd_journal_sendv()</function> is similar to <function>sd_journal_send()</function> but takes an
 108     array of <varname>struct iovec</varname> (as defined in <filename>uio.h</filename>, see <citerefentry
 109     project='man-pages'><refentrytitle>readv</refentrytitle><manvolnum>3</manvolnum></citerefentry> for details)
 110     instead of the format string. Each structure should reference one field of the entry to submit. The second argument
 111     specifies the number of structures in the array.  <function>sd_journal_sendv()</function> is particularly useful to
 112     submit binary objects to the journal where that is necessary. Note that this function will not strip trailing
 113     whitespace of the passed fields, but passes the specified data along unmodified. This is different from both
 114     <function>sd_journal_print()</function> and <function>sd_journal_send()</function> described above, which are based
 115     on format strings, and do strip trailing whitespace.</para>
 116
 117     <para><function>sd_journal_perror()</function> is a similar to
 118     <citerefentry project='die-net'><refentrytitle>perror</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 119     and writes a message to the journal that consists of the passed
 120     string, suffixed with ": " and a human-readable representation of
 121     the current error code stored in
 122     <citerefentry project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 123     If the message string is passed as <constant>NULL</constant> or
 124     empty string, only the error string representation will be
 125     written, prefixed with nothing. An additional journal field ERRNO=
 126     is included in the entry containing the numeric error code
 127     formatted as decimal string. The log priority used is
 128     <constant>LOG_ERR</constant> (3).</para>
 129
 130     <para>Note that <function>sd_journal_send()</function> is a
 131     wrapper around <function>sd_journal_sendv()</function> to make it
 132     easier to use when only text strings shall be submitted. Also, the
 133     following two calls are mostly equivalent:</para>
 134
 135     <programlisting>sd_journal_print(LOG_INFO, "Hello World, this is PID %lu!", (unsigned long) getpid());
 136
 137 sd_journal_send("MESSAGE=Hello World, this is PID %lu!", (unsigned long) getpid(),
 138                 "PRIORITY=%i", LOG_INFO,
 139                 NULL);</programlisting>
 140
 141     <para>Note that these calls implicitly add fields for the source
 142     file, function name and code line where invoked. This is
 143     implemented with macros. If this is not desired, it can be turned
 144     off by defining SD_JOURNAL_SUPPRESS_LOCATION before including
 145     <filename>sd-journal.h</filename>.</para>
 146
 147     <para><citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 148     and <function>sd_journal_print()</function> may
 149     largely be used interchangeably
 150     functionality-wise. However, note that log messages
 151     logged via the former take a different path to the
 152     journal server than the later, and hence global
 153     chronological ordering between the two streams cannot
 154     be guaranteed. Using
 155     <function>sd_journal_print()</function> has the
 156     benefit of logging source code line, filenames, and
 157     functions as metadata along all entries, and
 158     guaranteeing chronological ordering with structured
 159     log entries that are generated via
 160     <function>sd_journal_send()</function>. Using
 161     <function>syslog()</function> has the benefit of being
 162     more portable.</para>
 163   </refsect1>
 164
 165   <refsect1>
 166     <title>Return Value</title>
 167
 168     <para>The five calls return 0 on success or a negative errno-style error code. The <citerefentry
 169     project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry> variable itself is
 170     not altered.</para>
 171
 172     <para>If
 173     <citerefentry><refentrytitle>systemd-journald</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 174     is not running (the socket is not present), those functions do
 175     nothing, and also return 0.</para>
 176   </refsect1>
 177
 178   <refsect1>
 179     <title>Thread safety</title>
 180     <para>All functions listed here are thread-safe and may be called in parallel from multiple threads.</para>
 181
 182     <para><function>sd_journal_sendv()</function> is "async signal safe" in the meaning of <citerefentry
 183     project='man-pages'><refentrytitle>signal-safety</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 184     </para>
 185
 186     <para><function>sd_journal_print</function>,
 187     <function>sd_journal_printv</function>,
 188     <function>sd_journal_send</function>, and
 189     <function>sd_journal_perror</function> are
 190     not async signal safe.</para>
 191   </refsect1>
 192
 193   <xi:include href="libsystemd-pkgconfig.xml" />
 194
 195   <refsect1>
 196     <title>See Also</title>
 197
 198     <para>
 199       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 200       <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 201       <citerefentry><refentrytitle>sd_journal_stream_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 202       <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 203       <citerefentry project='die-net'><refentrytitle>perror</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 204       <citerefentry project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 205       <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 206       <citerefentry project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 207       <citerefentry project='man-pages'><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 208     </para>
 209   </refsect1>
 210
 211 </refentry>