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   This file is part of systemd.
   9
  10   Copyright 2012 Lennart Poettering
  11 -->
  12
  13 <refentry id="sd_journal_print">
  14
  15   <refentryinfo>
  16     <title>sd_journal_print</title>
  17     <productname>systemd</productname>
  18
  19     <authorgroup>
  20       <author>
  21         <contrib>Developer</contrib>
  22         <firstname>Lennart</firstname>
  23         <surname>Poettering</surname>
  24         <email>lennart@poettering.net</email>
  25       </author>
  26     </authorgroup>
  27   </refentryinfo>
  28
  29   <refmeta>
  30     <refentrytitle>sd_journal_print</refentrytitle>
  31     <manvolnum>3</manvolnum>
  32   </refmeta>
  33
  34   <refnamediv>
  35     <refname>sd_journal_print</refname>
  36     <refname>sd_journal_printv</refname>
  37     <refname>sd_journal_send</refname>
  38     <refname>sd_journal_sendv</refname>
  39     <refname>sd_journal_perror</refname>
  40     <refname>SD_JOURNAL_SUPPRESS_LOCATION</refname>
  41     <refpurpose>Submit log entries to the journal</refpurpose>
  42   </refnamediv>
  43
  44   <refsynopsisdiv>
  45     <funcsynopsis>
  46       <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>
  47
  48       <funcprototype>
  49         <funcdef>int <function>sd_journal_print</function></funcdef>
  50         <paramdef>int <parameter>priority</parameter></paramdef>
  51         <paramdef>const char *<parameter>format</parameter></paramdef>
  52         <paramdef>…</paramdef>
  53       </funcprototype>
  54
  55       <funcprototype>
  56         <funcdef>int <function>sd_journal_printv</function></funcdef>
  57         <paramdef>int <parameter>priority</parameter></paramdef>
  58         <paramdef>const char *<parameter>format</parameter></paramdef>
  59         <paramdef>va_list <parameter>ap</parameter></paramdef>
  60       </funcprototype>
  61
  62       <funcprototype>
  63         <funcdef>int <function>sd_journal_send</function></funcdef>
  64         <paramdef>const char *<parameter>format</parameter></paramdef>
  65         <paramdef>…</paramdef>
  66       </funcprototype>
  67
  68       <funcprototype>
  69         <funcdef>int <function>sd_journal_sendv</function></funcdef>
  70         <paramdef>const struct iovec *<parameter>iov</parameter></paramdef>
  71         <paramdef>int <parameter>n</parameter></paramdef>
  72       </funcprototype>
  73
  74       <funcprototype>
  75         <funcdef>int <function>sd_journal_perror</function></funcdef>
  76         <paramdef>const char *<parameter>message</parameter></paramdef>
  77       </funcprototype>
  78
  79     </funcsynopsis>
  80   </refsynopsisdiv>
  81
  82   <refsect1>
  83     <title>Description</title>
  84
  85     <para><function>sd_journal_print()</function> may be used to submit simple, plain text log entries to the system
  86     journal. The first argument is a priority value. This is followed by a format string and its parameters, similar to
  87     <citerefentry project='man-pages'><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry> or
  88     <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
  89     The priority value is one of <constant>LOG_EMERG</constant>, <constant>LOG_ALERT</constant>,
  90     <constant>LOG_CRIT</constant>, <constant>LOG_ERR</constant>, <constant>LOG_WARNING</constant>,
  91     <constant>LOG_NOTICE</constant>, <constant>LOG_INFO</constant>, <constant>LOG_DEBUG</constant>, as defined in
  92     <filename>syslog.h</filename>, see <citerefentry
  93     project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry> for details. It is
  94     recommended to use this call to submit log messages in the application locale or system locale and in UTF-8 format,
  95     but no such restrictions are enforced. Note that log messages written using this function are generally not
  96     expected to end in a new-line character. However, as all trailing whitespace (including spaces, new-lines,
  97     tabulators and carriage returns) are automatically stripped from the logged string, it is acceptable to specify one
  98     (or more). Empty lines (after trailing whitespace removal) are suppressed. On non-empty lines, leading whitespace
  99     (as well as inner whitespace) is left unmodified. </para>
 100
 101     <para><function>sd_journal_printv()</function> is similar to
 102     <function>sd_journal_print()</function> but takes a variable
 103     argument list encapsulated in an object of type
 104     <varname>va_list</varname> (see
 105     <citerefentry project='man-pages'><refentrytitle>stdarg</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 106     for more information) instead of the format string. It is
 107     otherwise equivalent in behavior.</para>
 108
 109     <para><function>sd_journal_send()</function> may be used to submit structured log entries to the system journal. It
 110     takes a series of format strings, each immediately followed by their associated parameters, terminated by
 111     <constant>NULL</constant>. The strings passed should be of the format <literal>VARIABLE=value</literal>.  The
 112     variable name must be in uppercase and consist only of characters, numbers and underscores, and may not begin with
 113     an underscore. (All assignments that do not follow this syntax will be ignored.) The value can be of any size and
 114     format. It is highly recommended to submit text strings formatted in the UTF-8 character encoding only, and submit
 115     binary fields only when formatting in UTF-8 strings is not sensible. A number of well-known fields are defined, see
 116     <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
 117     details, but additional application defined fields may be used. A variable may be assigned more than one value per
 118     entry. If this function is used, trailing whitespace is automatically removed from each formatted field.</para>
 119
 120     <para><function>sd_journal_sendv()</function> is similar to <function>sd_journal_send()</function> but takes an
 121     array of <varname>struct iovec</varname> (as defined in <filename>uio.h</filename>, see <citerefentry
 122     project='man-pages'><refentrytitle>readv</refentrytitle><manvolnum>3</manvolnum></citerefentry> for details)
 123     instead of the format string. Each structure should reference one field of the entry to submit. The second argument
 124     specifies the number of structures in the array.  <function>sd_journal_sendv()</function> is particularly useful to
 125     submit binary objects to the journal where that is necessary. Note that this function will not strip trailing
 126     whitespace of the passed fields, but passes the specified data along unmodified. This is different from both
 127     <function>sd_journal_print()</function> and <function>sd_journal_send()</function> described above, which are based
 128     on format strings, and do strip trailing whitespace.</para>
 129
 130     <para><function>sd_journal_perror()</function> is a similar to
 131     <citerefentry project='die-net'><refentrytitle>perror</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 132     and writes a message to the journal that consists of the passed
 133     string, suffixed with ": " and a human-readable representation of
 134     the current error code stored in
 135     <citerefentry project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 136     If the message string is passed as <constant>NULL</constant> or
 137     empty string, only the error string representation will be
 138     written, prefixed with nothing. An additional journal field ERRNO=
 139     is included in the entry containing the numeric error code
 140     formatted as decimal string. The log priority used is
 141     <constant>LOG_ERR</constant> (3).</para>
 142
 143     <para>Note that <function>sd_journal_send()</function> is a
 144     wrapper around <function>sd_journal_sendv()</function> to make it
 145     easier to use when only text strings shall be submitted. Also, the
 146     following two calls are mostly equivalent:</para>
 147
 148     <programlisting>sd_journal_print(LOG_INFO, "Hello World, this is PID %lu!", (unsigned long) getpid());
 149
 150 sd_journal_send("MESSAGE=Hello World, this is PID %lu!", (unsigned long) getpid(),
 151                 "PRIORITY=%i", LOG_INFO,
 152                 NULL);</programlisting>
 153
 154     <para>Note that these calls implicitly add fields for the source
 155     file, function name and code line where invoked. This is
 156     implemented with macros. If this is not desired, it can be turned
 157     off by defining SD_JOURNAL_SUPPRESS_LOCATION before including
 158     <filename>sd-journal.h</filename>.</para>
 159
 160     <para><citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 161     and <function>sd_journal_print()</function> may
 162     largely be used interchangeably
 163     functionality-wise. However, note that log messages
 164     logged via the former take a different path to the
 165     journal server than the later, and hence global
 166     chronological ordering between the two streams cannot
 167     be guaranteed. Using
 168     <function>sd_journal_print()</function> has the
 169     benefit of logging source code line, filenames, and
 170     functions as metadata along all entries, and
 171     guaranteeing chronological ordering with structured
 172     log entries that are generated via
 173     <function>sd_journal_send()</function>. Using
 174     <function>syslog()</function> has the benefit of being
 175     more portable.</para>
 176   </refsect1>
 177
 178   <refsect1>
 179     <title>Return Value</title>
 180
 181     <para>The five calls return 0 on success or a negative errno-style error code. The <citerefentry
 182     project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry> variable itself is
 183     not altered.</para>
 184
 185     <para>If
 186     <citerefentry><refentrytitle>systemd-journald</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 187     is not running (the socket is not present), those functions do
 188     nothing, and also return 0.</para>
 189   </refsect1>
 190
 191   <refsect1>
 192     <title>Thread safety</title>
 193     <para>All functions listed here are thread-safe and may be called in parallel from multiple threads.</para>
 194
 195     <para><function>sd_journal_sendv()</function> is "async signal safe" in the meaning of <citerefentry
 196     project='man-pages'><refentrytitle>signal-safety</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 197     </para>
 198
 199     <para><function>sd_journal_print</function>,
 200     <function>sd_journal_printv</function>,
 201     <function>sd_journal_send</function>, and
 202     <function>sd_journal_perror</function> are
 203     not async signal safe.</para>
 204   </refsect1>
 205
 206   <refsect1>
 207     <title>Notes</title>
 208
 209     <para>The <function>sd_journal_print()</function>, <function>sd_journal_printv()</function>,
 210     <function>sd_journal_send()</function>, <function>sd_journal_sendv()</function> and
 211     <function>sd_journal_perror()</function> interfaces are available as a shared library, which can be compiled and
 212     linked to with the <constant>libsystemd</constant> <citerefentry
 213     project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> file.</para>
 214   </refsect1>
 215
 216   <refsect1>
 217     <title>See Also</title>
 218
 219     <para>
 220       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 221       <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 222       <citerefentry><refentrytitle>sd_journal_stream_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 223       <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 224       <citerefentry project='die-net'><refentrytitle>perror</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 225       <citerefentry project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 226       <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 227       <citerefentry project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 228       <citerefentry project='man-pages'><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 229     </para>
 230   </refsect1>
 231
 232 </refentry>