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   Copyright 2012 Lennart Poettering
   9 -->
  10
  11 <refentry id="sd_journal_print" xmlns:xi="http://www.w3.org/2001/XInclude">
  12
  13   <refentryinfo>
  14     <title>sd_journal_print</title>
  15     <productname>systemd</productname>
  16
  17     <authorgroup>
  18       <author>
  19         <contrib>Developer</contrib>
  20         <firstname>Lennart</firstname>
  21         <surname>Poettering</surname>
  22         <email>lennart@poettering.net</email>
  23       </author>
  24     </authorgroup>
  25   </refentryinfo>
  26
  27   <refmeta>
  28     <refentrytitle>sd_journal_print</refentrytitle>
  29     <manvolnum>3</manvolnum>
  30   </refmeta>
  31
  32   <refnamediv>
  33     <refname>sd_journal_print</refname>
  34     <refname>sd_journal_printv</refname>
  35     <refname>sd_journal_send</refname>
  36     <refname>sd_journal_sendv</refname>
  37     <refname>sd_journal_perror</refname>
  38     <refname>SD_JOURNAL_SUPPRESS_LOCATION</refname>
  39     <refpurpose>Submit log entries to the journal</refpurpose>
  40   </refnamediv>
  41
  42   <refsynopsisdiv>
  43     <funcsynopsis>
  44       <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>
  45
  46       <funcprototype>
  47         <funcdef>int <function>sd_journal_print</function></funcdef>
  48         <paramdef>int <parameter>priority</parameter></paramdef>
  49         <paramdef>const char *<parameter>format</parameter></paramdef>
  50         <paramdef>…</paramdef>
  51       </funcprototype>
  52
  53       <funcprototype>
  54         <funcdef>int <function>sd_journal_printv</function></funcdef>
  55         <paramdef>int <parameter>priority</parameter></paramdef>
  56         <paramdef>const char *<parameter>format</parameter></paramdef>
  57         <paramdef>va_list <parameter>ap</parameter></paramdef>
  58       </funcprototype>
  59
  60       <funcprototype>
  61         <funcdef>int <function>sd_journal_send</function></funcdef>
  62         <paramdef>const char *<parameter>format</parameter></paramdef>
  63         <paramdef>…</paramdef>
  64       </funcprototype>
  65
  66       <funcprototype>
  67         <funcdef>int <function>sd_journal_sendv</function></funcdef>
  68         <paramdef>const struct iovec *<parameter>iov</parameter></paramdef>
  69         <paramdef>int <parameter>n</parameter></paramdef>
  70       </funcprototype>
  71
  72       <funcprototype>
  73         <funcdef>int <function>sd_journal_perror</function></funcdef>
  74         <paramdef>const char *<parameter>message</parameter></paramdef>
  75       </funcprototype>
  76
  77     </funcsynopsis>
  78   </refsynopsisdiv>
  79
  80   <refsect1>
  81     <title>Description</title>
  82
  83     <para><function>sd_journal_print()</function> may be used to submit simple, plain text log entries to the system
  84     journal. The first argument is a priority value. This is followed by a format string and its parameters, similar to
  85     <citerefentry project='man-pages'><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry> or
  86     <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
  87     The priority value is one of <constant>LOG_EMERG</constant>, <constant>LOG_ALERT</constant>,
  88     <constant>LOG_CRIT</constant>, <constant>LOG_ERR</constant>, <constant>LOG_WARNING</constant>,
  89     <constant>LOG_NOTICE</constant>, <constant>LOG_INFO</constant>, <constant>LOG_DEBUG</constant>, as defined in
  90     <filename>syslog.h</filename>, see <citerefentry
  91     project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry> for details. It is
  92     recommended to use this call to submit log messages in the application locale or system locale and in UTF-8 format,
  93     but no such restrictions are enforced. Note that log messages written using this function are generally not
  94     expected to end in a new-line character. However, as all trailing whitespace (including spaces, new-lines,
  95     tabulators and carriage returns) are automatically stripped from the logged string, it is acceptable to specify one
  96     (or more). Empty lines (after trailing whitespace removal) are suppressed. On non-empty lines, leading whitespace
  97     (as well as inner whitespace) is left unmodified. </para>
  98
  99     <para><function>sd_journal_printv()</function> is similar to
 100     <function>sd_journal_print()</function> but takes a variable
 101     argument list encapsulated in an object of type
 102     <varname>va_list</varname> (see
 103     <citerefentry project='man-pages'><refentrytitle>stdarg</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 104     for more information) instead of the format string. It is
 105     otherwise equivalent in behavior.</para>
 106
 107     <para><function>sd_journal_send()</function> may be used to submit structured log entries to the system journal. It
 108     takes a series of format strings, each immediately followed by their associated parameters, terminated by
 109     <constant>NULL</constant>. The strings passed should be of the format <literal>VARIABLE=value</literal>.  The
 110     variable name must be in uppercase and consist only of characters, numbers and underscores, and may not begin with
 111     an underscore. (All assignments that do not follow this syntax will be ignored.) The value can be of any size and
 112     format. It is highly recommended to submit text strings formatted in the UTF-8 character encoding only, and submit
 113     binary fields only when formatting in UTF-8 strings is not sensible. A number of well-known fields are defined, see
 114     <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
 115     details, but additional application defined fields may be used. A variable may be assigned more than one value per
 116     entry. If this function is used, trailing whitespace is automatically removed from each formatted field.</para>
 117
 118     <para><function>sd_journal_sendv()</function> is similar to <function>sd_journal_send()</function> but takes an
 119     array of <varname>struct iovec</varname> (as defined in <filename>uio.h</filename>, see <citerefentry
 120     project='man-pages'><refentrytitle>readv</refentrytitle><manvolnum>3</manvolnum></citerefentry> for details)
 121     instead of the format string. Each structure should reference one field of the entry to submit. The second argument
 122     specifies the number of structures in the array.  <function>sd_journal_sendv()</function> is particularly useful to
 123     submit binary objects to the journal where that is necessary. Note that this function will not strip trailing
 124     whitespace of the passed fields, but passes the specified data along unmodified. This is different from both
 125     <function>sd_journal_print()</function> and <function>sd_journal_send()</function> described above, which are based
 126     on format strings, and do strip trailing whitespace.</para>
 127
 128     <para><function>sd_journal_perror()</function> is a similar to
 129     <citerefentry project='die-net'><refentrytitle>perror</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 130     and writes a message to the journal that consists of the passed
 131     string, suffixed with ": " and a human-readable representation of
 132     the current error code stored in
 133     <citerefentry project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 134     If the message string is passed as <constant>NULL</constant> or
 135     empty string, only the error string representation will be
 136     written, prefixed with nothing. An additional journal field ERRNO=
 137     is included in the entry containing the numeric error code
 138     formatted as decimal string. The log priority used is
 139     <constant>LOG_ERR</constant> (3).</para>
 140
 141     <para>Note that <function>sd_journal_send()</function> is a
 142     wrapper around <function>sd_journal_sendv()</function> to make it
 143     easier to use when only text strings shall be submitted. Also, the
 144     following two calls are mostly equivalent:</para>
 145
 146     <programlisting>sd_journal_print(LOG_INFO, "Hello World, this is PID %lu!", (unsigned long) getpid());
 147
 148 sd_journal_send("MESSAGE=Hello World, this is PID %lu!", (unsigned long) getpid(),
 149                 "PRIORITY=%i", LOG_INFO,
 150                 NULL);</programlisting>
 151
 152     <para>Note that these calls implicitly add fields for the source
 153     file, function name and code line where invoked. This is
 154     implemented with macros. If this is not desired, it can be turned
 155     off by defining SD_JOURNAL_SUPPRESS_LOCATION before including
 156     <filename>sd-journal.h</filename>.</para>
 157
 158     <para><citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 159     and <function>sd_journal_print()</function> may
 160     largely be used interchangeably
 161     functionality-wise. However, note that log messages
 162     logged via the former take a different path to the
 163     journal server than the later, and hence global
 164     chronological ordering between the two streams cannot
 165     be guaranteed. Using
 166     <function>sd_journal_print()</function> has the
 167     benefit of logging source code line, filenames, and
 168     functions as metadata along all entries, and
 169     guaranteeing chronological ordering with structured
 170     log entries that are generated via
 171     <function>sd_journal_send()</function>. Using
 172     <function>syslog()</function> has the benefit of being
 173     more portable.</para>
 174   </refsect1>
 175
 176   <refsect1>
 177     <title>Return Value</title>
 178
 179     <para>The five calls return 0 on success or a negative errno-style error code. The <citerefentry
 180     project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry> variable itself is
 181     not altered.</para>
 182
 183     <para>If
 184     <citerefentry><refentrytitle>systemd-journald</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 185     is not running (the socket is not present), those functions do
 186     nothing, and also return 0.</para>
 187   </refsect1>
 188
 189   <refsect1>
 190     <title>Thread safety</title>
 191     <para>All functions listed here are thread-safe and may be called in parallel from multiple threads.</para>
 192
 193     <para><function>sd_journal_sendv()</function> is "async signal safe" in the meaning of <citerefentry
 194     project='man-pages'><refentrytitle>signal-safety</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 195     </para>
 196
 197     <para><function>sd_journal_print</function>,
 198     <function>sd_journal_printv</function>,
 199     <function>sd_journal_send</function>, and
 200     <function>sd_journal_perror</function> are
 201     not async signal safe.</para>
 202   </refsect1>
 203
 204   <xi:include href="libsystemd-pkgconfig.xml" />
 205
 206   <refsect1>
 207     <title>See Also</title>
 208
 209     <para>
 210       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 211       <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 212       <citerefentry><refentrytitle>sd_journal_stream_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 213       <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 214       <citerefentry project='die-net'><refentrytitle>perror</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 215       <citerefentry project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 216       <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 217       <citerefentry project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 218       <citerefentry project='man-pages'><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 219     </para>
 220   </refsect1>
 221
 222 </refentry>