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man: updates to the passive target section
[elogind.git] / man / sd_journal_stream_fd.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
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8   Copyright 2012 Lennart Poettering
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23
24 <refentry id="sd_journal_stream_fd">
25
26         <refentryinfo>
27                 <title>sd_journal_stream_fd</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_stream_fd</refentrytitle>
42                 <manvolnum>3</manvolnum>
43         </refmeta>
44
45         <refnamediv>
46                 <refname>sd_journal_stream_fd</refname>
47                 <refpurpose>Create log stream file descriptor to the journal</refpurpose>
48         </refnamediv>
49
50         <refsynopsisdiv>
51                 <funcsynopsis>
52                         <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>
53
54                         <funcprototype>
55                                 <funcdef>int <function>sd_journal_stream_fd</function></funcdef>
56                                 <paramdef>const char *<parameter>identifier</parameter></paramdef>
57                                 <paramdef>int <parameter>priority</parameter></paramdef>
58                                 <paramdef>int <parameter>level_prefix</parameter></paramdef>
59                         </funcprototype>
60
61                 </funcsynopsis>
62         </refsynopsisdiv>
63
64         <refsect1>
65                 <title>Description</title>
66
67                 <para><function>sd_journal_stream_fd()</function> may
68                 be used to create a log stream file descriptor. Log
69                 messages written to this file descriptor as simple
70                 newline-separated text strings are written to the
71                 journal. This file descriptor can be used internally
72                 by applications or be made standard output or standard
73                 error of other processes executed.</para>
74
75                 <para><function>sd_journal_stream_fd()</function>
76                 takes a short program identifier string as first
77                 argument, which will be written to the journal as
78                 _SYSLOG_IDENTIFIER= field for each log entry (see
79                 <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>
80                 for more information). The second argument shall be
81                 the default priority level for all messages. The
82                 priority level is one of <constant>LOG_EMERG</constant>,
83                 <constant>LOG_ALERT</constant>,
84                 <constant>LOG_CRIT</constant>,
85                 <constant>LOG_ERR</constant>,
86                 <constant>LOG_WARNING</constant>,
87                 <constant>LOG_NOTICE</constant>,
88                 <constant>LOG_INFO</constant>,
89                 <constant>LOG_DEBUG</constant>, as defined in
90                 <filename>syslog.h</filename>, see
91                 <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
92                 for details. The third argument is a boolean: if true
93                 kernel-style log priority level prefixes (such as
94                 <constant>SD_WARNING</constant>) are interpreted, see
95                 <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>
96                 for more information.</para>
97
98                 <para>It is recommended that applications log UTF-8
99                 messages only with this API, but this is not
100                 enforced.</para>
101
102         </refsect1>
103
104         <refsect1>
105                 <title>Return Value</title>
106
107                 <para>The call returns a valid write-only file descriptor on success or a
108                 negative errno-style error code.</para>
109         </refsect1>
110
111         <refsect1>
112                 <title>Notes</title>
113
114                 <para>The <function>sd_journal_stream_fd()</function>
115                 interface is available as a shared library, which can
116                 be compiled and linked to with the
117                 <constant>libsystemd</constant> <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
118                 file.</para>
119         </refsect1>
120
121         <refsect1>
122                 <title>Examples</title>
123
124                 <para>Creating a log stream suitable for
125                 <citerefentry><refentrytitle>fprintf</refentrytitle><manvolnum>3</manvolnum></citerefentry>:</para>
126
127                 <programlisting>#include &lt;syslog.h&gt;
128 #include &lt;stdio.h&gt;
129 #include &lt;string.h&gt;
130 #include &lt;unistd.h&gt;
131 #include &lt;systemd/sd-journal.h&gt;
132 #include &lt;systemd/sd-daemon.h&gt;
133
134 int main(int argc, char *argv[]) {
135         int fd;
136         FILE *log;
137         fd = sd_journal_stream_fd("test", LOG_INFO, 1);
138         if (fd &lt; 0) {
139                 fprintf(stderr, "Failed to create stream fd: %s\n", strerror(-fd));
140                 return 1;
141         }
142         log = fdopen(fd, "w");
143         if (!log) {
144                 fprintf(stderr, "Failed to create file object: %m\n");
145                 close(fd);
146                 return 1;
147         }
148         fprintf(log, "Hello World!\n");
149         fprintf(log, SD_WARNING "This is a warning!\n");
150         fclose(log);
151         return 0;
152 }</programlisting>
153
154         </refsect1>
155
156         <refsect1>
157                 <title>See Also</title>
158
159                 <para>
160                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
161                         <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
162                         <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
163                         <citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
164                         <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
165                         <citerefentry><refentrytitle>fprintf</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
166                         <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>
167                 </para>
168         </refsect1>
169
170 </refentry>