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     Note that currently the resulting message will be truncated to <constant>LINE_MAX - 8</constant>.
  74     The priority value is one of <constant>LOG_EMERG</constant>, <constant>LOG_ALERT</constant>,
  75     <constant>LOG_CRIT</constant>, <constant>LOG_ERR</constant>, <constant>LOG_WARNING</constant>,
  76     <constant>LOG_NOTICE</constant>, <constant>LOG_INFO</constant>, <constant>LOG_DEBUG</constant>, as defined in
  77     <filename>syslog.h</filename>, see <citerefentry
  78     project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry> for details. It is
  79     recommended to use this call to submit log messages in the application locale or system locale and in UTF-8 format,
  80     but no such restrictions are enforced. Note that log messages written using this function are generally not
  81     expected to end in a new-line character. However, as all trailing whitespace (including spaces, new-lines,
  82     tabulators and carriage returns) are automatically stripped from the logged string, it is acceptable to specify one
  83     (or more). Empty lines (after trailing whitespace removal) are suppressed. On non-empty lines, leading whitespace
  84     (as well as inner whitespace) is left unmodified. </para>
  85
  86     <para><function>sd_journal_printv()</function> is similar to
  87     <function>sd_journal_print()</function> but takes a variable
  88     argument list encapsulated in an object of type
  89     <varname>va_list</varname> (see
  90     <citerefentry project='man-pages'><refentrytitle>stdarg</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  91     for more information) instead of the format string. It is
  92     otherwise equivalent in behavior.</para>
  93
  94     <para><function>sd_journal_send()</function> may be used to submit structured log entries to the system journal. It
  95     takes a series of format strings, each immediately followed by their associated parameters, terminated by
  96     <constant>NULL</constant>. The strings passed should be of the format <literal>VARIABLE=value</literal>.  The
  97     variable name must be in uppercase and consist only of characters, numbers and underscores, and may not begin with
  98     an underscore. (All assignments that do not follow this syntax will be ignored.) The value can be of any size and
  99     format. It is highly recommended to submit text strings formatted in the UTF-8 character encoding only, and submit
 100     binary fields only when formatting in UTF-8 strings is not sensible. A number of well-known fields are defined, see
 101     <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
 102     details, but additional application defined fields may be used. A variable may be assigned more than one value per
 103     entry. If this function is used, trailing whitespace is automatically removed from each formatted field.</para>
 104
 105     <para><function>sd_journal_sendv()</function> is similar to <function>sd_journal_send()</function> but takes an
 106     array of <varname>struct iovec</varname> (as defined in <filename>uio.h</filename>, see <citerefentry
 107     project='man-pages'><refentrytitle>readv</refentrytitle><manvolnum>3</manvolnum></citerefentry> for details)
 108     instead of the format string. Each structure should reference one field of the entry to submit. The second argument
 109     specifies the number of structures in the array.  <function>sd_journal_sendv()</function> is particularly useful to
 110     submit binary objects to the journal where that is necessary. Note that this function will not strip trailing
 111     whitespace of the passed fields, but passes the specified data along unmodified. This is different from both
 112     <function>sd_journal_print()</function> and <function>sd_journal_send()</function> described above, which are based
 113     on format strings, and do strip trailing whitespace.</para>
 114
 115     <para><function>sd_journal_perror()</function> is a similar to
 116     <citerefentry project='die-net'><refentrytitle>perror</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 117     and writes a message to the journal that consists of the passed
 118     string, suffixed with ": " and a human-readable representation of
 119     the current error code stored in
 120     <citerefentry project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 121     If the message string is passed as <constant>NULL</constant> or
 122     empty string, only the error string representation will be
 123     written, prefixed with nothing. An additional journal field ERRNO=
 124     is included in the entry containing the numeric error code
 125     formatted as decimal string. The log priority used is
 126     <constant>LOG_ERR</constant> (3).</para>
 127
 128     <para>Note that <function>sd_journal_send()</function> is a
 129     wrapper around <function>sd_journal_sendv()</function> to make it
 130     easier to use when only text strings shall be submitted. Also, the
 131     following two calls are mostly equivalent:</para>
 132
 133     <programlisting>sd_journal_print(LOG_INFO, "Hello World, this is PID %lu!", (unsigned long) getpid());
 134
 135 sd_journal_send("MESSAGE=Hello World, this is PID %lu!", (unsigned long) getpid(),
 136                 "PRIORITY=%i", LOG_INFO,
 137                 NULL);</programlisting>
 138
 139     <para>Note that these calls implicitly add fields for the source
 140     file, function name and code line where invoked. This is
 141     implemented with macros. If this is not desired, it can be turned
 142     off by defining SD_JOURNAL_SUPPRESS_LOCATION before including
 143     <filename>sd-journal.h</filename>.</para>
 144
 145     <para><citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 146     and <function>sd_journal_print()</function> may
 147     largely be used interchangeably
 148     functionality-wise. However, note that log messages
 149     logged via the former take a different path to the
 150     journal server than the later, and hence global
 151     chronological ordering between the two streams cannot
 152     be guaranteed. Using
 153     <function>sd_journal_print()</function> has the
 154     benefit of logging source code line, filenames, and
 155     functions as metadata along all entries, and
 156     guaranteeing chronological ordering with structured
 157     log entries that are generated via
 158     <function>sd_journal_send()</function>. Using
 159     <function>syslog()</function> has the benefit of being
 160     more portable.</para>
 161   </refsect1>
 162
 163   <refsect1>
 164     <title>Return Value</title>
 165
 166     <para>The five calls return 0 on success or a negative errno-style error code. The <citerefentry
 167     project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry> variable itself is
 168     not altered.</para>
 169
 170     <para>If
 171     <citerefentry><refentrytitle>systemd-journald</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 172     is not running (the socket is not present), those functions do
 173     nothing, and also return 0.</para>
 174   </refsect1>
 175
 176   <refsect1>
 177     <title>Thread safety</title>
 178
 179     <xi:include href="threads-aware.xml" xpointer="safe"/>
 180
 181     <para><function>sd_journal_sendv()</function> is "async signal safe" in the meaning of <citerefentry
 182     project='man-pages'><refentrytitle>signal-safety</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 183     </para>
 184
 185     <para><function>sd_journal_print</function>,
 186     <function>sd_journal_printv</function>,
 187     <function>sd_journal_send</function>, and
 188     <function>sd_journal_perror</function> are
 189     not async signal safe.</para>
 190   </refsect1>
 191
 192   <xi:include href="libsystemd-pkgconfig.xml" />
 193
 194   <refsect1>
 195     <title>See Also</title>
 196
 197     <para>
 198       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 199       <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 200       <citerefentry><refentrytitle>sd_journal_stream_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 201       <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 202       <citerefentry project='die-net'><refentrytitle>perror</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 203       <citerefentry project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 204       <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 205       <citerefentry project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 206       <citerefentry project='man-pages'><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 207     </para>
 208   </refsect1>
 209
 210 </refentry>