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socket: don't allow mixing of accepting and non-accepting sockets in the same unit
[elogind.git] / man / sd_notify.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 2010 Lennart Poettering
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23
24 <refentry id="sd_notify">
25
26         <refentryinfo>
27                 <title>sd_notify</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_notify</refentrytitle>
42                 <manvolnum>3</manvolnum>
43         </refmeta>
44
45         <refnamediv>
46                 <refname>sd_notify</refname>
47                 <refname>sd_notifyf</refname>
48                 <refpurpose>Notify init system about start-up completion and other daemon status changes</refpurpose>
49         </refnamediv>
50
51         <refsynopsisdiv>
52                 <funcsynopsis>
53                         <funcsynopsisinfo>#include "sd-daemon.h"</funcsynopsisinfo>
54
55                         <funcprototype>
56                                 <funcdef>int <function>sd_notify</function></funcdef>
57                                 <paramdef>int <parameter>unset_environment</parameter></paramdef>
58                                 <paramdef>const char *<parameter>state</parameter></paramdef>
59                         </funcprototype>
60
61                         <funcprototype>
62                                 <funcdef>int <function>sd_notifyf</function></funcdef>
63                                 <paramdef>int <parameter>unset_environment</parameter></paramdef>
64                                 <paramdef>const char *<parameter>format</parameter></paramdef>
65                                 <paramdef>...</paramdef>
66                         </funcprototype>
67                 </funcsynopsis>
68         </refsynopsisdiv>
69
70         <refsect1>
71                 <title>Description</title>
72                 <para><function>sd_notify()</function> shall be called
73                 by a daemon to notify the init system about status
74                 changes. It can be used to send arbitrary information,
75                 encoded in an environment-block-like string. Most
76                 importantly it can be used for start-up completion
77                 notification.</para>
78
79                 <para>If the <parameter>unset_environment</parameter>
80                 parameter is non-zero <function>sd_notify()</function>
81                 will unset the <varname>$NOTIFY_SOCKET</varname>
82                 environment variable before returning (regardless
83                 whether the function call itself succeeded or
84                 not). Further calls to
85                 <function>sd_notify()</function> will then fail, but
86                 the variable is no longer inherited by child
87                 processes.</para>
88
89                 <para>The <parameter>state</parameter> parameter
90                 should contain an newline-seperated list of variable
91                 assignments, similar in style to an environment
92                 block. A trailing newline is implied if none is
93                 specified. The string may contain any kind of variable
94                 assignments, but the following shall be considered
95                 well-known:</para>
96
97                 <variablelist>
98                         <varlistentry>
99                                 <term>READY=1</term>
100
101                                 <listitem><para>Tells the init system
102                                 that daemon startup is finished. This
103                                 is only used by systemd if the service
104                                 definition file has Type=notify
105                                 set. The passed argument is a boolean
106                                 "1" or "0". Since there is little
107                                 value in signalling non-readiness, the
108                                 only value daemons should send is
109                                 "READY=1".</para></listitem>
110                         </varlistentry>
111
112                         <varlistentry>
113                                 <term>STATUS=...</term>
114
115                                 <listitem><para>Passes a single-line
116                                 status string back to the init system
117                                 that describes the daemon state. This
118                                 is free-form and can be used for
119                                 various purposes: general state
120                                 feedback, fsck-like programs could
121                                 pass completion percentages and
122                                 failing programs could pass a human
123                                 readable error message. Example:
124                                 "STATUS=Completed 66% of file system
125                                 check..."</para></listitem>
126                         </varlistentry>
127
128                         <varlistentry>
129                                 <term>ERRNO=...</term>
130
131                                 <listitem><para>If a daemon fails, the
132                                 errno-style error code, formatted as
133                                 string. Example: "ERRNO=2" for
134                                 ENOENT.</para></listitem>
135                         </varlistentry>
136
137                         <varlistentry>
138                                 <term>BUSERROR=...</term>
139
140                                 <listitem><para>If a daemon fails, the
141                                 D-Bus error-style error code. Example:
142                                 "BUSERROR=org.freedesktop.DBus.Error.TimedOut"</para></listitem>
143                         </varlistentry>
144
145                         <varlistentry>
146                                 <term>MAINPID=...</term>
147
148                                 <listitem><para>The main pid of the
149                                 daemon, in case the init system did
150                                 not fork off the process
151                                 itself. Example:
152                                 "MAINPID=4711"</para></listitem>
153                         </varlistentry>
154                 </variablelist>
155
156                 <para>It is recommended to prefix variable names that
157                 are not shown in the list above with
158                 <varname>X_</varname> to avoid namespace
159                 clashes.</para>
160
161                 <para>Note that systemd will accept status data sent
162                 from a daemon only if the
163                 <varname>NotifyAccess=</varname> option is correctly
164                 set in the service definition file. See
165                 <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
166                 for details.</para>
167
168                 <para><function>sd_notifyf()</function> is similar to
169                 <function>sd_notifyf()</function> but takes a
170                 <function>printf()</function>-like format string plus
171                 arguments.</para>
172         </refsect1>
173
174         <refsect1>
175                 <title>Return Value</title>
176
177                 <para>On failure, these calls return a negative
178                 errno-style error code. If
179                 <varname>$NOTIFY_SOCKET</varname> was not set and
180                 hence no status data could be sent, 0 is returned. If
181                 the status was sent these functions return with a
182                 positive return value. In order to support both, init
183                 systems that implement this scheme and those which
184                 don't, it is generally recommended to ignore the return
185                 value of this call.</para>
186         </refsect1>
187
188         <refsect1>
189                 <title>Notes</title>
190
191                 <para>These functions are provided by the reference
192                 implementation of APIs for new-style daemons and
193                 distributed with the systemd package. The algorithms
194                 they implement are simple, and can easily be
195                 reimplemented in daemons if it is important to support
196                 this interface without using the reference
197                 implementation.</para>
198
199                 <para>Internally, these functions send a single
200                 datagram with the state string as payload to the
201                 AF_UNIX socket referenced in the
202                 <varname>$NOTIFY_SOCKET</varname> environment
203                 variable. If the first character of
204                 <varname>$NOTIFY_SOCKET</varname> is @ the string is
205                 understood as Linux abstract namespace socket. The
206                 datagram is accompanied by the process credentials of
207                 the sending daemon, using SCM_CREDENTIALS.</para>
208
209                 <para>For details about the algorithm check the
210                 liberally licensed reference implementation sources:
211                 <ulink url="http://cgit.freedesktop.org/systemd/tree/src/sd-daemon.c"/>
212                 resp. <ulink
213                 url="http://cgit.freedesktop.org/systemd/tree/src/sd-daemon.h"/></para>
214
215                 <para><function>sd_notify()</function> and
216                 <function>sd_notifyf()</function> are implemented in
217                 the reference implementation's drop-in
218                 <filename>sd-daemon.c</filename> and
219                 <filename>sd-daemon.h</filename> files. It is
220                 recommended that applications consuming these APIs
221                 copy the implementation into their source tree. For
222                 more details about the reference implementation see
223                 <citerefentry><refentrytitle>sd_daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry></para>
224
225                 <para>If -DDISABLE_SYSTEMD is set during compilation
226                 this function will always return 0 and otherwise
227                 become a NOP.</para>
228         </refsect1>
229
230         <refsect1>
231                 <title>Environment</title>
232
233                 <variablelist>
234                         <varlistentry>
235                                 <term><varname>$NOTIFY_SOCKET</varname></term>
236
237                                 <listitem><para>Set by the init system
238                                 for supervised processes for status
239                                 and start-up completion
240                                 notification. This environment variable
241                                 specifies the socket
242                                 <function>sd_notify()</function> talks
243                                 to. See above for details.</para></listitem>
244                         </varlistentry>
245                 </variablelist>
246         </refsect1>
247
248         <refsect1>
249                 <title>Examples</title>
250
251                 <example>
252                         <title>Start-up Notification</title>
253
254                         <para>When a daemon finished starting up, it
255                         might issue the following call to notify
256                         the init system:</para>
257
258                         <programlisting>sd_notify(0, "READY=1");</programlisting>
259                 </example>
260
261                 <example>
262                         <title>Extended Start-up Notification</title>
263
264                         <para>A daemon could send the following after
265                         completing initialization:</para>
266
267                         <programlisting>sd_notifyf(0, "READY=1\n"
268               "STATUS=Processing requests...\n"
269               "MAINPID=%lu",
270               (unsigned long) getpid());</programlisting>
271                 </example>
272
273                 <example>
274                         <title>Error Cause Notification</title>
275
276                         <para>A daemon could send the following shortly before exiting, on failure</para>
277
278                         <programlisting>sd_notifyf(0, "STATUS=Failed to start up: %s\n"
279               "ERRNO=%i",
280               strerror(errno),
281               errno);</programlisting>
282                 </example>
283         </refsect1>
284
285         <refsect1>
286                 <title>See Also</title>
287                 <para>
288                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
289                         <citerefentry><refentrytitle>sd_daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
290                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
291                         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
292                 </para>
293         </refsect1>
294
295 </refentry>