man/sd_journal_print.xml

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  23
  24 <refentry id="sd_journal_print">
  25
  26   <refentryinfo>
  27     <title>sd_journal_print</title>
  28     <productname>systemd</productname>
  29
  30     <authorgroup>
  31       <author>
  32         <contrib>Developer</contrib>
  33         <firstname>Lennart</firstname>
  34         <surname>Poettering</surname>
  35         <email>lennart@poettering.net</email>
  36       </author>
  37     </authorgroup>
  38   </refentryinfo>
  39
  40   <refmeta>
  41     <refentrytitle>sd_journal_print</refentrytitle>
  42     <manvolnum>3</manvolnum>
  43   </refmeta>
  44
  45   <refnamediv>
  46     <refname>sd_journal_print</refname>
  47     <refname>sd_journal_printv</refname>
  48     <refname>sd_journal_send</refname>
  49     <refname>sd_journal_sendv</refname>
  50     <refname>sd_journal_perror</refname>
  51     <refname>SD_JOURNAL_SUPPRESS_LOCATION</refname>
  52     <refpurpose>Submit log entries to the journal</refpurpose>
  53   </refnamediv>
  54
  55   <refsynopsisdiv>
  56     <funcsynopsis>
  57       <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>
  58
  59       <funcprototype>
  60         <funcdef>int <function>sd_journal_print</function></funcdef>
  61         <paramdef>int <parameter>priority</parameter></paramdef>
  62         <paramdef>const char *<parameter>format</parameter></paramdef>
  63         <paramdef>…</paramdef>
  64       </funcprototype>
  65
  66       <funcprototype>
  67         <funcdef>int <function>sd_journal_printv</function></funcdef>
  68         <paramdef>int <parameter>priority</parameter></paramdef>
  69         <paramdef>const char *<parameter>format</parameter></paramdef>
  70         <paramdef>va_list <parameter>ap</parameter></paramdef>
  71       </funcprototype>
  72
  73       <funcprototype>
  74         <funcdef>int <function>sd_journal_send</function></funcdef>
  75         <paramdef>const char *<parameter>format</parameter></paramdef>
  76         <paramdef>…</paramdef>
  77       </funcprototype>
  78
  79       <funcprototype>
  80         <funcdef>int <function>sd_journal_sendv</function></funcdef>
  81         <paramdef>const struct iovec *<parameter>iov</parameter></paramdef>
  82         <paramdef>int <parameter>n</parameter></paramdef>
  83       </funcprototype>
  84
  85       <funcprototype>
  86         <funcdef>int <function>sd_journal_perror</function></funcdef>
  87         <paramdef>const char *<parameter>message</parameter></paramdef>
  88       </funcprototype>
  89
  90     </funcsynopsis>
  91   </refsynopsisdiv>
  92
  93   <refsect1>
  94     <title>Description</title>
  95
  96     <para><function>sd_journal_print()</function> may be used to submit simple, plain text log entries to the system
  97     journal. The first argument is a priority value. This is followed by a format string and its parameters, similar to
  98     <citerefentry project='man-pages'><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry> or
  99     <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 100     The priority value is one of <constant>LOG_EMERG</constant>, <constant>LOG_ALERT</constant>,
 101     <constant>LOG_CRIT</constant>, <constant>LOG_ERR</constant>, <constant>LOG_WARNING</constant>,
 102     <constant>LOG_NOTICE</constant>, <constant>LOG_INFO</constant>, <constant>LOG_DEBUG</constant>, as defined in
 103     <filename>syslog.h</filename>, see <citerefentry
 104     project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry> for details. It is
 105     recommended to use this call to submit log messages in the application locale or system locale and in UTF-8 format,
 106     but no such restrictions are enforced. Note that log messages written using this function are generally not
 107     expected to end in a new-line character. However, as all trailing whitespace (including spaces, new-lines,
 108     tabulators and carriage returns) are automatically stripped from the logged string, it is acceptable to specify one
 109     (or more). Empty lines (after trailing whitespace removal) are suppressed. On non-empty lines, leading whitespace
 110     (as well as inner whitespace) is left unmodified. </para>
 111
 112     <para><function>sd_journal_printv()</function> is similar to
 113     <function>sd_journal_print()</function> but takes a variable
 114     argument list encapsulated in an object of type
 115     <varname>va_list</varname> (see
 116     <citerefentry project='man-pages'><refentrytitle>stdarg</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 117     for more information) instead of the format string. It is
 118     otherwise equivalent in behavior.</para>
 119
 120     <para><function>sd_journal_send()</function> may be used to submit structured log entries to the system journal. It
 121     takes a series of format strings, each immediately followed by their associated parameters, terminated by
 122     <constant>NULL</constant>. The strings passed should be of the format <literal>VARIABLE=value</literal>.  The
 123     variable name must be in uppercase and consist only of characters, numbers and underscores, and may not begin with
 124     an underscore. (All assignments that do not follow this syntax will be ignored.) The value can be of any size and
 125     format. It is highly recommended to submit text strings formatted in the UTF-8 character encoding only, and submit
 126     binary fields only when formatting in UTF-8 strings is not sensible. A number of well-known fields are defined, see
 127     <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
 128     details, but additional application defined fields may be used. A variable may be assigned more than one value per
 129     entry. If this function is used, trailing whitespace is automatically removed from each formatted field.</para>
 130
 131     <para><function>sd_journal_sendv()</function> is similar to <function>sd_journal_send()</function> but takes an
 132     array of <varname>struct iovec</varname> (as defined in <filename>uio.h</filename>, see <citerefentry
 133     project='man-pages'><refentrytitle>readv</refentrytitle><manvolnum>3</manvolnum></citerefentry> for details)
 134     instead of the format string. Each structure should reference one field of the entry to submit. The second argument
 135     specifies the number of structures in the array.  <function>sd_journal_sendv()</function> is particularly useful to
 136     submit binary objects to the journal where that is necessary. Note that this function wil not strip trailing
 137     whitespace of the passed fields, but passes the specified data along unmodified. This is different from both
 138     <function>sd_journal_print()</function> and <function>sd_journal_send()</function> described above, which are based
 139     on format strings, and do strip trailing whitespace.</para>
 140
 141     <para><function>sd_journal_perror()</function> is a similar to
 142     <citerefentry project='die-net'><refentrytitle>perror</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 143     and writes a message to the journal that consists of the passed
 144     string, suffixed with ": " and a human-readable representation of
 145     the current error code stored in
 146     <citerefentry project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 147     If the message string is passed as <constant>NULL</constant> or
 148     empty string, only the error string representation will be
 149     written, prefixed with nothing. An additional journal field ERRNO=
 150     is included in the entry containing the numeric error code
 151     formatted as decimal string. The log priority used is
 152     <constant>LOG_ERR</constant> (3).</para>
 153
 154     <para>Note that <function>sd_journal_send()</function> is a
 155     wrapper around <function>sd_journal_sendv()</function> to make it
 156     easier to use when only text strings shall be submitted. Also, the
 157     following two calls are mostly equivalent:</para>
 158
 159     <programlisting>sd_journal_print(LOG_INFO, "Hello World, this is PID %lu!", (unsigned long) getpid());
 160
 161 sd_journal_send("MESSAGE=Hello World, this is PID %lu!", (unsigned long) getpid(),
 162                 "PRIORITY=%i", LOG_INFO,
 163                 NULL);</programlisting>
 164
 165     <para>Note that these calls implicitly add fields for the source
 166     file, function name and code line where invoked. This is
 167     implemented with macros. If this is not desired, it can be turned
 168     off by defining SD_JOURNAL_SUPPRESS_LOCATION before including
 169     <filename>sd-journal.h</filename>.</para>
 170
 171     <para><citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 172     and <function>sd_journal_print()</function> may
 173     largely be used interchangeably
 174     functionality-wise. However, note that log messages
 175     logged via the former take a different path to the
 176     journal server than the later, and hence global
 177     chronological ordering between the two streams cannot
 178     be guaranteed. Using
 179     <function>sd_journal_print()</function> has the
 180     benefit of logging source code line, filenames, and
 181     functions as metadata along all entries, and
 182     guaranteeing chronological ordering with structured
 183     log entries that are generated via
 184     <function>sd_journal_send()</function>. Using
 185     <function>syslog()</function> has the benefit of being
 186     more portable.</para>
 187   </refsect1>
 188
 189   <refsect1>
 190     <title>Return Value</title>
 191
 192     <para>The five calls return 0 on success or a negative errno-style error code. The <citerefentry
 193     project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry> variable itself is
 194     not altered.</para>
 195
 196     <para>If
 197     <citerefentry><refentrytitle>systemd-journald</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 198     is not running (the socket is not present), those functions do
 199     nothing, and also return 0.</para>
 200   </refsect1>
 201
 202   <refsect1>
 203     <title>Thread safety</title>
 204     <para>All functions listed here are thread-safe and may be called in parallel from multiple threads.</para>
 205
 206     <para><function>sd_journal_sendv()</function> is "async signal safe" in the meaning of
 207     <citerefentry project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 208     </para>
 209
 210     <para><function>sd_journal_print</function>,
 211     <function>sd_journal_printv</function>,
 212     <function>sd_journal_send</function>, and
 213     <function>sd_journal_perror</function> are
 214     not async signal safe.</para>
 215   </refsect1>
 216
 217   <refsect1>
 218     <title>Notes</title>
 219
 220     <para>The <function>sd_journal_print()</function>, <function>sd_journal_printv()</function>,
 221     <function>sd_journal_send()</function>, <function>sd_journal_sendv()</function> and
 222     <function>sd_journal_perror()</function> interfaces are available as a shared library, which can be compiled and
 223     linked to with the <constant>libsystemd</constant> <citerefentry
 224     project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> file.</para>
 225   </refsect1>
 226
 227   <refsect1>
 228     <title>See Also</title>
 229
 230     <para>
 231       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 232       <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 233       <citerefentry><refentrytitle>sd_journal_stream_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 234       <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 235       <citerefentry project='die-net'><refentrytitle>perror</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 236       <citerefentry project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 237       <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 238       <citerefentry project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 239       <citerefentry project='man-pages'><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 240     </para>
 241   </refsect1>
 242
 243 </refentry>