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     <refname>sd_journal_print_with_location</refname>
  26     <refname>sd_journal_printv_with_location</refname>
  27     <refname>sd_journal_send_with_location</refname>
  28     <refname>sd_journal_sendv_with_location</refname>
  29     <refname>sd_journal_perror_with_location</refname>
  30
  31     <refpurpose>Submit log entries to the journal</refpurpose>
  32   </refnamediv>
  33
  34   <refsynopsisdiv>
  35     <funcsynopsis>
  36       <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>
  37
  38       <funcprototype>
  39         <funcdef>int <function>sd_journal_print</function></funcdef>
  40         <paramdef>int <parameter>priority</parameter></paramdef>
  41         <paramdef>const char *<parameter>format</parameter></paramdef>
  42         <paramdef>…</paramdef>
  43       </funcprototype>
  44
  45       <funcprototype>
  46         <funcdef>int <function>sd_journal_printv</function></funcdef>
  47         <paramdef>int <parameter>priority</parameter></paramdef>
  48         <paramdef>const char *<parameter>format</parameter></paramdef>
  49         <paramdef>va_list <parameter>ap</parameter></paramdef>
  50       </funcprototype>
  51
  52       <funcprototype>
  53         <funcdef>int <function>sd_journal_send</function></funcdef>
  54         <paramdef>const char *<parameter>format</parameter></paramdef>
  55         <paramdef>…</paramdef>
  56       </funcprototype>
  57
  58       <funcprototype>
  59         <funcdef>int <function>sd_journal_sendv</function></funcdef>
  60         <paramdef>const struct iovec *<parameter>iov</parameter></paramdef>
  61         <paramdef>int <parameter>n</parameter></paramdef>
  62       </funcprototype>
  63
  64       <funcprototype>
  65         <funcdef>int <function>sd_journal_perror</function></funcdef>
  66         <paramdef>const char *<parameter>message</parameter></paramdef>
  67       </funcprototype>
  68
  69       <funcprototype>
  70         <funcdef>int <function>sd_journal_print_with_location</function></funcdef>
  71         <paramdef>const char *<parameter>file</parameter></paramdef>
  72         <paramdef>const char *<parameter>line</parameter></paramdef>
  73         <paramdef>const char *<parameter>func</parameter></paramdef>
  74         <paramdef>int <parameter>priority</parameter></paramdef>
  75         <paramdef>const char *<parameter>format</parameter></paramdef>
  76         <paramdef>…</paramdef>
  77       </funcprototype>
  78
  79       <funcprototype>
  80         <funcdef>int <function>sd_journal_printv_with_location</function></funcdef>
  81         <paramdef>int <parameter>priority</parameter></paramdef>
  82         <paramdef>const char *<parameter>file</parameter></paramdef>
  83         <paramdef>const char *<parameter>line</parameter></paramdef>
  84         <paramdef>const char *<parameter>func</parameter></paramdef>
  85         <paramdef>const char *<parameter>format</parameter></paramdef>
  86         <paramdef>va_list <parameter>ap</parameter></paramdef>
  87       </funcprototype>
  88
  89       <funcprototype>
  90         <funcdef>int <function>sd_journal_send_with_location</function></funcdef>
  91         <paramdef>const char *<parameter>file</parameter></paramdef>
  92         <paramdef>const char *<parameter>line</parameter></paramdef>
  93         <paramdef>const char *<parameter>func</parameter></paramdef>
  94         <paramdef>const char *<parameter>format</parameter></paramdef>
  95         <paramdef>…</paramdef>
  96       </funcprototype>
  97
  98       <funcprototype>
  99         <funcdef>int <function>sd_journal_sendv_with_location</function></funcdef>
 100         <paramdef>const char *<parameter>file</parameter></paramdef>
 101         <paramdef>const char *<parameter>line</parameter></paramdef>
 102         <paramdef>const char *<parameter>func</parameter></paramdef>
 103         <paramdef>const struct iovec *<parameter>iov</parameter></paramdef>
 104         <paramdef>int <parameter>n</parameter></paramdef>
 105       </funcprototype>
 106
 107       <funcprototype>
 108         <funcdef>int <function>sd_journal_perror_with_location</function></funcdef>
 109         <paramdef>const char *<parameter>file</parameter></paramdef>
 110         <paramdef>const char *<parameter>line</parameter></paramdef>
 111         <paramdef>const char *<parameter>func</parameter></paramdef>
 112         <paramdef>const char *<parameter>message</parameter></paramdef>
 113       </funcprototype>
 114     </funcsynopsis>
 115   </refsynopsisdiv>
 116
 117   <refsect1>
 118     <title>Description</title>
 119
 120     <para><function>sd_journal_print()</function> may be used to submit simple, plain text log entries to the system
 121     journal. The first argument is a priority value. This is followed by a format string and its parameters, similar to
 122     <citerefentry project='man-pages'><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry> or
 123     <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 124     Note that currently the resulting message will be truncated to <constant>LINE_MAX - 8</constant>.
 125     The priority value is one of <constant>LOG_EMERG</constant>, <constant>LOG_ALERT</constant>,
 126     <constant>LOG_CRIT</constant>, <constant>LOG_ERR</constant>, <constant>LOG_WARNING</constant>,
 127     <constant>LOG_NOTICE</constant>, <constant>LOG_INFO</constant>, <constant>LOG_DEBUG</constant>, as defined in
 128     <filename>syslog.h</filename>, see <citerefentry
 129     project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry> for details. It is
 130     recommended to use this call to submit log messages in the application locale or system locale and in UTF-8 format,
 131     but no such restrictions are enforced. Note that log messages written using this function are generally not
 132     expected to end in a new-line character. However, as all trailing whitespace (including spaces, new-lines,
 133     tabulators and carriage returns) are automatically stripped from the logged string, it is acceptable to specify one
 134     (or more). Empty lines (after trailing whitespace removal) are suppressed. On non-empty lines, leading whitespace
 135     (as well as inner whitespace) is left unmodified. </para>
 136
 137     <para><function>sd_journal_printv()</function> is similar to
 138     <function>sd_journal_print()</function> but takes a variable
 139     argument list encapsulated in an object of type
 140     <varname>va_list</varname> (see
 141     <citerefentry project='man-pages'><refentrytitle>stdarg</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 142     for more information) instead of the format string. It is
 143     otherwise equivalent in behavior.</para>
 144
 145     <para><function>sd_journal_send()</function> may be used to submit structured log entries to the system journal. It
 146     takes a series of format strings, each immediately followed by their associated parameters, terminated by
 147     <constant>NULL</constant>. The strings passed should be of the format <literal>VARIABLE=value</literal>.  The
 148     variable name must be in uppercase and consist only of characters, numbers and underscores, and may not begin with
 149     an underscore. (All assignments that do not follow this syntax will be ignored.) The value can be of any size and
 150     format. It is highly recommended to submit text strings formatted in the UTF-8 character encoding only, and submit
 151     binary fields only when formatting in UTF-8 strings is not sensible. A number of well-known fields are defined, see
 152     <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
 153     details, but additional application defined fields may be used. A variable may be assigned more than one value per
 154     entry. If this function is used, trailing whitespace is automatically removed from each formatted field.</para>
 155
 156     <para><function>sd_journal_sendv()</function> is similar to <function>sd_journal_send()</function> but takes an
 157     array of <varname>struct iovec</varname> (as defined in <filename>uio.h</filename>, see <citerefentry
 158     project='man-pages'><refentrytitle>readv</refentrytitle><manvolnum>3</manvolnum></citerefentry> for details)
 159     instead of the format string. Each structure should reference one field of the entry to submit. The second argument
 160     specifies the number of structures in the array.  <function>sd_journal_sendv()</function> is particularly useful to
 161     submit binary objects to the journal where that is necessary. Note that this function will not strip trailing
 162     whitespace of the passed fields, but passes the specified data along unmodified. This is different from both
 163     <function>sd_journal_print()</function> and <function>sd_journal_send()</function> described above, which are based
 164     on format strings, and do strip trailing whitespace.</para>
 165
 166     <para><function>sd_journal_perror()</function> is a similar to
 167     <citerefentry project='die-net'><refentrytitle>perror</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 168     and writes a message to the journal that consists of the passed
 169     string, suffixed with ": " and a human-readable representation of
 170     the current error code stored in
 171     <citerefentry project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 172     If the message string is passed as <constant>NULL</constant> or
 173     empty string, only the error string representation will be
 174     written, prefixed with nothing. An additional journal field ERRNO=
 175     is included in the entry containing the numeric error code
 176     formatted as decimal string. The log priority used is
 177     <constant>LOG_ERR</constant> (3).</para>
 178
 179     <para>Note that <function>sd_journal_send()</function> is a
 180     wrapper around <function>sd_journal_sendv()</function> to make it
 181     easier to use when only text strings shall be submitted. Also, the
 182     following two calls are mostly equivalent:</para>
 183
 184     <programlisting>sd_journal_print(LOG_INFO, "Hello World, this is PID %lu!", (unsigned long) getpid());
 185
 186 sd_journal_send("MESSAGE=Hello World, this is PID %lu!", (unsigned long) getpid(),
 187                 "PRIORITY=%i", LOG_INFO,
 188                 NULL);</programlisting>
 189
 190     <para>Note that these calls implicitly add fields for the source file, function name and code line where
 191     invoked. This is implemented with macros. If this is not desired, it can be turned off by defining
 192     <constant>SD_JOURNAL_SUPPRESS_LOCATION</constant> before including <filename>sd-journal.h</filename>.
 193     </para>
 194
 195     <para><function>sd_journal_print_with_location</function>,
 196     <function>sd_journal_printv_with_location</function>, <function>sd_journal_send_with_location</function>,
 197     <function>sd_journal_sendv_with_location</function>, and
 198     <function>sd_journal_perror_with_location</function> are similar to their counterparts without
 199     <literal>_with_location</literal>, but accept additional parameters to explicitly set the source file
 200     name, function, and line. Those arguments must contain valid journal entries including the variable name,
 201     e.g. <literal>CODE_FILE=src/foo.c</literal>, <literal>CODE_LINE=666</literal>,
 202     <literal>CODE_FUNC=myfunc</literal>. These variants are primarily useful when writing custom wrappers,
 203     for example in bindings for a different language.</para>
 204
 205     <para><citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 206     and <function>sd_journal_print()</function> may
 207     largely be used interchangeably
 208     functionality-wise. However, note that log messages
 209     logged via the former take a different path to the
 210     journal server than the later, and hence global
 211     chronological ordering between the two streams cannot
 212     be guaranteed. Using
 213     <function>sd_journal_print()</function> has the
 214     benefit of logging source code line, filenames, and
 215     functions as metadata along all entries, and
 216     guaranteeing chronological ordering with structured
 217     log entries that are generated via
 218     <function>sd_journal_send()</function>. Using
 219     <function>syslog()</function> has the benefit of being
 220     more portable.</para>
 221   </refsect1>
 222
 223   <refsect1>
 224     <title>Return Value</title>
 225
 226     <para>The ten functions return 0 on success or a negative errno-style error code. The
 227     <citerefentry project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 228     variable itself is not altered.</para>
 229
 230     <para>If
 231     <citerefentry><refentrytitle>systemd-journald</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 232     is not running (the socket is not present), those functions do
 233     nothing, and also return 0.</para>
 234   </refsect1>
 235
 236   <refsect1>
 237     <title>Thread safety</title>
 238
 239     <xi:include href="threads-aware.xml" xpointer="safe"/>
 240
 241     <para><function>sd_journal_sendv()</function> and <function>sd_journal_sendv_with_location()</function>
 242     are "async signal safe" in the meaning of
 243     <citerefentry project='man-pages'><refentrytitle>signal-safety</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 244     </para>
 245
 246     <para><function>sd_journal_print</function>,
 247     <function>sd_journal_printv</function>,
 248     <function>sd_journal_send</function>,
 249     <function>sd_journal_perror</function>,
 250     and their counterparts with <literal>_with_location</literal>
 251     are not async signal safe.</para>
 252   </refsect1>
 253
 254   <xi:include href="libsystemd-pkgconfig.xml" />
 255
 256   <refsect1>
 257     <title>See Also</title>
 258
 259     <para>
 260       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 261       <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 262       <citerefentry><refentrytitle>sd_journal_stream_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 263       <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 264       <citerefentry project='die-net'><refentrytitle>perror</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 265       <citerefentry project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 266       <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 267       <citerefentry project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 268       <citerefentry project='man-pages'><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 269     </para>
 270   </refsect1>
 271
 272 </refentry>