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246 lines
12 KiB
XML
246 lines
12 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!--
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SPDX-License-Identifier: LGPL-2.1+
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This file is part of systemd.
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Copyright 2012 Lennart Poettering
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systemd is free software; you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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systemd is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with systemd; If not, see <http://www.gnu.org/licenses/>.
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-->
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<refentry id="sd_journal_print">
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<refentryinfo>
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<title>sd_journal_print</title>
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<productname>systemd</productname>
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<authorgroup>
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<author>
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<contrib>Developer</contrib>
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<firstname>Lennart</firstname>
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<surname>Poettering</surname>
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<email>lennart@poettering.net</email>
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</author>
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</authorgroup>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_journal_print</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sd_journal_print</refname>
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<refname>sd_journal_printv</refname>
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<refname>sd_journal_send</refname>
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<refname>sd_journal_sendv</refname>
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<refname>sd_journal_perror</refname>
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<refname>SD_JOURNAL_SUPPRESS_LOCATION</refname>
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<refpurpose>Submit log entries to the journal</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <systemd/sd-journal.h></funcsynopsisinfo>
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<funcprototype>
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<funcdef>int <function>sd_journal_print</function></funcdef>
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<paramdef>int <parameter>priority</parameter></paramdef>
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<paramdef>const char *<parameter>format</parameter></paramdef>
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<paramdef>…</paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_journal_printv</function></funcdef>
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<paramdef>int <parameter>priority</parameter></paramdef>
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<paramdef>const char *<parameter>format</parameter></paramdef>
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<paramdef>va_list <parameter>ap</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_journal_send</function></funcdef>
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<paramdef>const char *<parameter>format</parameter></paramdef>
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<paramdef>…</paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_journal_sendv</function></funcdef>
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<paramdef>const struct iovec *<parameter>iov</parameter></paramdef>
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<paramdef>int <parameter>n</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_journal_perror</function></funcdef>
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<paramdef>const char *<parameter>message</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><function>sd_journal_print()</function> may be used to submit simple, plain text log entries to the system
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journal. The first argument is a priority value. This is followed by a format string and its parameters, similar to
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<citerefentry project='man-pages'><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry> or
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<citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
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The priority value is one of <constant>LOG_EMERG</constant>, <constant>LOG_ALERT</constant>,
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<constant>LOG_CRIT</constant>, <constant>LOG_ERR</constant>, <constant>LOG_WARNING</constant>,
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<constant>LOG_NOTICE</constant>, <constant>LOG_INFO</constant>, <constant>LOG_DEBUG</constant>, as defined in
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<filename>syslog.h</filename>, see <citerefentry
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project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry> for details. It is
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recommended to use this call to submit log messages in the application locale or system locale and in UTF-8 format,
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but no such restrictions are enforced. Note that log messages written using this function are generally not
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expected to end in a new-line character. However, as all trailing whitespace (including spaces, new-lines,
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tabulators and carriage returns) are automatically stripped from the logged string, it is acceptable to specify one
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(or more). Empty lines (after trailing whitespace removal) are suppressed. On non-empty lines, leading whitespace
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(as well as inner whitespace) is left unmodified. </para>
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<para><function>sd_journal_printv()</function> is similar to
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<function>sd_journal_print()</function> but takes a variable
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argument list encapsulated in an object of type
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<varname>va_list</varname> (see
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<citerefentry project='man-pages'><refentrytitle>stdarg</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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for more information) instead of the format string. It is
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otherwise equivalent in behavior.</para>
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<para><function>sd_journal_send()</function> may be used to submit structured log entries to the system journal. It
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takes a series of format strings, each immediately followed by their associated parameters, terminated by
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<constant>NULL</constant>. The strings passed should be of the format <literal>VARIABLE=value</literal>. The
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variable name must be in uppercase and consist only of characters, numbers and underscores, and may not begin with
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an underscore. (All assignments that do not follow this syntax will be ignored.) The value can be of any size and
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format. It is highly recommended to submit text strings formatted in the UTF-8 character encoding only, and submit
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binary fields only when formatting in UTF-8 strings is not sensible. A number of well-known fields are defined, see
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<citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
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details, but additional application defined fields may be used. A variable may be assigned more than one value per
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entry. If this function is used, trailing whitespace is automatically removed from each formatted field.</para>
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<para><function>sd_journal_sendv()</function> is similar to <function>sd_journal_send()</function> but takes an
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array of <varname>struct iovec</varname> (as defined in <filename>uio.h</filename>, see <citerefentry
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project='man-pages'><refentrytitle>readv</refentrytitle><manvolnum>3</manvolnum></citerefentry> for details)
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instead of the format string. Each structure should reference one field of the entry to submit. The second argument
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specifies the number of structures in the array. <function>sd_journal_sendv()</function> is particularly useful to
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submit binary objects to the journal where that is necessary. Note that this function will not strip trailing
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whitespace of the passed fields, but passes the specified data along unmodified. This is different from both
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<function>sd_journal_print()</function> and <function>sd_journal_send()</function> described above, which are based
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on format strings, and do strip trailing whitespace.</para>
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<para><function>sd_journal_perror()</function> is a similar to
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<citerefentry project='die-net'><refentrytitle>perror</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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and writes a message to the journal that consists of the passed
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string, suffixed with ": " and a human-readable representation of
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the current error code stored in
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<citerefentry project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
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If the message string is passed as <constant>NULL</constant> or
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empty string, only the error string representation will be
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written, prefixed with nothing. An additional journal field ERRNO=
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is included in the entry containing the numeric error code
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formatted as decimal string. The log priority used is
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<constant>LOG_ERR</constant> (3).</para>
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<para>Note that <function>sd_journal_send()</function> is a
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wrapper around <function>sd_journal_sendv()</function> to make it
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easier to use when only text strings shall be submitted. Also, the
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following two calls are mostly equivalent:</para>
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<programlisting>sd_journal_print(LOG_INFO, "Hello World, this is PID %lu!", (unsigned long) getpid());
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sd_journal_send("MESSAGE=Hello World, this is PID %lu!", (unsigned long) getpid(),
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"PRIORITY=%i", LOG_INFO,
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NULL);</programlisting>
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<para>Note that these calls implicitly add fields for the source
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file, function name and code line where invoked. This is
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implemented with macros. If this is not desired, it can be turned
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off by defining SD_JOURNAL_SUPPRESS_LOCATION before including
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<filename>sd-journal.h</filename>.</para>
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<para><citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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and <function>sd_journal_print()</function> may
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largely be used interchangeably
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functionality-wise. However, note that log messages
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logged via the former take a different path to the
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journal server than the later, and hence global
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chronological ordering between the two streams cannot
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be guaranteed. Using
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<function>sd_journal_print()</function> has the
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benefit of logging source code line, filenames, and
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functions as metadata along all entries, and
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guaranteeing chronological ordering with structured
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log entries that are generated via
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<function>sd_journal_send()</function>. Using
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<function>syslog()</function> has the benefit of being
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more portable.</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para>The five calls return 0 on success or a negative errno-style error code. The <citerefentry
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project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry> variable itself is
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not altered.</para>
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<para>If
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<citerefentry><refentrytitle>systemd-journald</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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is not running (the socket is not present), those functions do
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nothing, and also return 0.</para>
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</refsect1>
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<refsect1>
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<title>Thread safety</title>
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<para>All functions listed here are thread-safe and may be called in parallel from multiple threads.</para>
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<para><function>sd_journal_sendv()</function> is "async signal safe" in the meaning of <citerefentry
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project='man-pages'><refentrytitle>signal-safety</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
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</para>
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<para><function>sd_journal_print</function>,
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<function>sd_journal_printv</function>,
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<function>sd_journal_send</function>, and
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<function>sd_journal_perror</function> are
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not async signal safe.</para>
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</refsect1>
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<refsect1>
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<title>Notes</title>
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<para>The <function>sd_journal_print()</function>, <function>sd_journal_printv()</function>,
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<function>sd_journal_send()</function>, <function>sd_journal_sendv()</function> and
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<function>sd_journal_perror()</function> interfaces are available as a shared library, which can be compiled and
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linked to with the <constant>libsystemd</constant> <citerefentry
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project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> file.</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_journal_stream_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry project='die-net'><refentrytitle>perror</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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