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
  15     <authorgroup>
  16       <author>
  17         <contrib>Developer</contrib>
  18         <firstname>Lennart</firstname>
  19         <surname>Poettering</surname>
  20         <email>lennart@poettering.net</email>
  21       </author>
  22     </authorgroup>
  23   </refentryinfo>
  24
  25   <refmeta>
  26     <refentrytitle>sd_journal_print</refentrytitle>
  27     <manvolnum>3</manvolnum>
  28   </refmeta>
  29
  30   <refnamediv>
  31     <refname>sd_journal_print</refname>
  32     <refname>sd_journal_printv</refname>
  33     <refname>sd_journal_send</refname>
  34     <refname>sd_journal_sendv</refname>
  35     <refname>sd_journal_perror</refname>
  36     <refname>SD_JOURNAL_SUPPRESS_LOCATION</refname>
  37     <refpurpose>Submit log entries to the journal</refpurpose>
  38   </refnamediv>
  39
  40   <refsynopsisdiv>
  41     <funcsynopsis>
  42       <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>
  43
  44       <funcprototype>
  45         <funcdef>int <function>sd_journal_print</function></funcdef>
  46         <paramdef>int <parameter>priority</parameter></paramdef>
  47         <paramdef>const char *<parameter>format</parameter></paramdef>
  48         <paramdef>…</paramdef>
  49       </funcprototype>
  50
  51       <funcprototype>
  52         <funcdef>int <function>sd_journal_printv</function></funcdef>
  53         <paramdef>int <parameter>priority</parameter></paramdef>
  54         <paramdef>const char *<parameter>format</parameter></paramdef>
  55         <paramdef>va_list <parameter>ap</parameter></paramdef>
  56       </funcprototype>
  57
  58       <funcprototype>
  59         <funcdef>int <function>sd_journal_send</function></funcdef>
  60         <paramdef>const char *<parameter>format</parameter></paramdef>
  61         <paramdef>…</paramdef>
  62       </funcprototype>
  63
  64       <funcprototype>
  65         <funcdef>int <function>sd_journal_sendv</function></funcdef>
  66         <paramdef>const struct iovec *<parameter>iov</parameter></paramdef>
  67         <paramdef>int <parameter>n</parameter></paramdef>
  68       </funcprototype>
  69
  70       <funcprototype>
  71         <funcdef>int <function>sd_journal_perror</function></funcdef>
  72         <paramdef>const char *<parameter>message</parameter></paramdef>
  73       </funcprototype>
  74
  75     </funcsynopsis>
  76   </refsynopsisdiv>
  77
  78   <refsect1>
  79     <title>Description</title>
  80
  81     <para><function>sd_journal_print()</function> may be used to submit simple, plain text log entries to the system
  82     journal. The first argument is a priority value. This is followed by a format string and its parameters, similar to
  83     <citerefentry project='man-pages'><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry> or
  84     <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
  85     The priority value is one of <constant>LOG_EMERG</constant>, <constant>LOG_ALERT</constant>,
  86     <constant>LOG_CRIT</constant>, <constant>LOG_ERR</constant>, <constant>LOG_WARNING</constant>,
  87     <constant>LOG_NOTICE</constant>, <constant>LOG_INFO</constant>, <constant>LOG_DEBUG</constant>, as defined in
  88     <filename>syslog.h</filename>, see <citerefentry
  89     project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry> for details. It is
  90     recommended to use this call to submit log messages in the application locale or system locale and in UTF-8 format,
  91     but no such restrictions are enforced. Note that log messages written using this function are generally not
  92     expected to end in a new-line character. However, as all trailing whitespace (including spaces, new-lines,
  93     tabulators and carriage returns) are automatically stripped from the logged string, it is acceptable to specify one
  94     (or more). Empty lines (after trailing whitespace removal) are suppressed. On non-empty lines, leading whitespace
  95     (as well as inner whitespace) is left unmodified. </para>
  96
  97     <para><function>sd_journal_printv()</function> is similar to
  98     <function>sd_journal_print()</function> but takes a variable
  99     argument list encapsulated in an object of type
 100     <varname>va_list</varname> (see
 101     <citerefentry project='man-pages'><refentrytitle>stdarg</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 102     for more information) instead of the format string. It is
 103     otherwise equivalent in behavior.</para>
 104
 105     <para><function>sd_journal_send()</function> may be used to submit structured log entries to the system journal. It
 106     takes a series of format strings, each immediately followed by their associated parameters, terminated by
 107     <constant>NULL</constant>. The strings passed should be of the format <literal>VARIABLE=value</literal>.  The
 108     variable name must be in uppercase and consist only of characters, numbers and underscores, and may not begin with
 109     an underscore. (All assignments that do not follow this syntax will be ignored.) The value can be of any size and
 110     format. It is highly recommended to submit text strings formatted in the UTF-8 character encoding only, and submit
 111     binary fields only when formatting in UTF-8 strings is not sensible. A number of well-known fields are defined, see
 112     <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
 113     details, but additional application defined fields may be used. A variable may be assigned more than one value per
 114     entry. If this function is used, trailing whitespace is automatically removed from each formatted field.</para>
 115
 116     <para><function>sd_journal_sendv()</function> is similar to <function>sd_journal_send()</function> but takes an
 117     array of <varname>struct iovec</varname> (as defined in <filename>uio.h</filename>, see <citerefentry
 118     project='man-pages'><refentrytitle>readv</refentrytitle><manvolnum>3</manvolnum></citerefentry> for details)
 119     instead of the format string. Each structure should reference one field of the entry to submit. The second argument
 120     specifies the number of structures in the array.  <function>sd_journal_sendv()</function> is particularly useful to
 121     submit binary objects to the journal where that is necessary. Note that this function will not strip trailing
 122     whitespace of the passed fields, but passes the specified data along unmodified. This is different from both
 123     <function>sd_journal_print()</function> and <function>sd_journal_send()</function> described above, which are based
 124     on format strings, and do strip trailing whitespace.</para>
 125
 126     <para><function>sd_journal_perror()</function> is a similar to
 127     <citerefentry project='die-net'><refentrytitle>perror</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 128     and writes a message to the journal that consists of the passed
 129     string, suffixed with ": " and a human-readable representation of
 130     the current error code stored in
 131     <citerefentry project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 132     If the message string is passed as <constant>NULL</constant> or
 133     empty string, only the error string representation will be
 134     written, prefixed with nothing. An additional journal field ERRNO=
 135     is included in the entry containing the numeric error code
 136     formatted as decimal string. The log priority used is
 137     <constant>LOG_ERR</constant> (3).</para>
 138
 139     <para>Note that <function>sd_journal_send()</function> is a
 140     wrapper around <function>sd_journal_sendv()</function> to make it
 141     easier to use when only text strings shall be submitted. Also, the
 142     following two calls are mostly equivalent:</para>
 143
 144     <programlisting>sd_journal_print(LOG_INFO, "Hello World, this is PID %lu!", (unsigned long) getpid());
 145
 146 sd_journal_send("MESSAGE=Hello World, this is PID %lu!", (unsigned long) getpid(),
 147                 "PRIORITY=%i", LOG_INFO,
 148                 NULL);</programlisting>
 149
 150     <para>Note that these calls implicitly add fields for the source
 151     file, function name and code line where invoked. This is
 152     implemented with macros. If this is not desired, it can be turned
 153     off by defining SD_JOURNAL_SUPPRESS_LOCATION before including
 154     <filename>sd-journal.h</filename>.</para>
 155
 156     <para><citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 157     and <function>sd_journal_print()</function> may
 158     largely be used interchangeably
 159     functionality-wise. However, note that log messages
 160     logged via the former take a different path to the
 161     journal server than the later, and hence global
 162     chronological ordering between the two streams cannot
 163     be guaranteed. Using
 164     <function>sd_journal_print()</function> has the
 165     benefit of logging source code line, filenames, and
 166     functions as metadata along all entries, and
 167     guaranteeing chronological ordering with structured
 168     log entries that are generated via
 169     <function>sd_journal_send()</function>. Using
 170     <function>syslog()</function> has the benefit of being
 171     more portable.</para>
 172   </refsect1>
 173
 174   <refsect1>
 175     <title>Return Value</title>
 176
 177     <para>The five calls return 0 on success or a negative errno-style error code. The <citerefentry
 178     project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry> variable itself is
 179     not altered.</para>
 180
 181     <para>If
 182     <citerefentry><refentrytitle>systemd-journald</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 183     is not running (the socket is not present), those functions do
 184     nothing, and also return 0.</para>
 185   </refsect1>
 186
 187   <refsect1>
 188     <title>Thread safety</title>
 189     <para>All functions listed here are thread-safe and may be called in parallel from multiple threads.</para>
 190
 191     <para><function>sd_journal_sendv()</function> is "async signal safe" in the meaning of <citerefentry
 192     project='man-pages'><refentrytitle>signal-safety</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 193     </para>
 194
 195     <para><function>sd_journal_print</function>,
 196     <function>sd_journal_printv</function>,
 197     <function>sd_journal_send</function>, and
 198     <function>sd_journal_perror</function> are
 199     not async signal safe.</para>
 200   </refsect1>
 201
 202   <xi:include href="libsystemd-pkgconfig.xml" />
 203
 204   <refsect1>
 205     <title>See Also</title>
 206
 207     <para>
 208       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 209       <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 210       <citerefentry><refentrytitle>sd_journal_stream_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 211       <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 212       <citerefentry project='die-net'><refentrytitle>perror</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 213       <citerefentry project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 214       <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 215       <citerefentry project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 216       <citerefentry project='man-pages'><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 217     </para>
 218   </refsect1>
 219
 220 </refentry>