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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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7
8   Copyright 2010 Lennart Poettering
9
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22 -->
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 service manager about start-up completion and other daemon status changes</refpurpose>
49         </refnamediv>
50
51         <refsynopsisdiv>
52                 <funcsynopsis>
53                         <funcsynopsisinfo>#include &lt;systemd/sd-daemon.h&gt;</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 a newline-separated 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 signaling 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
155                         <varlistentry>
156                                 <term>WATCHDOG=1</term>
157
158                                 <listitem><para>Tells systemd to
159                                 update the watchdog timestamp. This is
160                                 the keep-alive ping that services need
161                                 to issue in regular intervals if
162                                 <varname>WatchdogSec=</varname> is
163                                 enabled for it. See
164                                 <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
165                                 for details. It is recommended to send
166                                 this message if the
167                                 <varname>WATCHDOG_USEC=</varname>
168                                 environment variable has been set for
169                                 the service process, in every half the
170                                 time interval that is specified in the
171                                 variable.</para></listitem>
172                         </varlistentry>
173                 </variablelist>
174
175                 <para>It is recommended to prefix variable names that
176                 are not shown in the list above with
177                 <varname>X_</varname> to avoid namespace
178                 clashes.</para>
179
180                 <para>Note that systemd will accept status data sent
181                 from a daemon only if the
182                 <varname>NotifyAccess=</varname> option is correctly
183                 set in the service definition file. See
184                 <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
185                 for details.</para>
186
187                 <para><function>sd_notifyf()</function> is similar to
188                 <function>sd_notify()</function> but takes a
189                 <function>printf()</function>-like format string plus
190                 arguments.</para>
191         </refsect1>
192
193         <refsect1>
194                 <title>Return Value</title>
195
196                 <para>On failure, these calls return a negative
197                 errno-style error code. If
198                 <varname>$NOTIFY_SOCKET</varname> was not set and
199                 hence no status data could be sent, 0 is returned. If
200                 the status was sent, these functions return with a
201                 positive return value. In order to support both, init
202                 systems that implement this scheme and those which
203                 do not, it is generally recommended to ignore the return
204                 value of this call.</para>
205         </refsect1>
206
207         <refsect1>
208                 <title>Notes</title>
209
210                 <para>These functions are provided by the reference
211                 implementation of APIs for new-style daemons and
212                 distributed with the systemd package. The algorithms
213                 they implement are simple, and can easily be
214                 reimplemented in daemons if it is important to support
215                 this interface without using the reference
216                 implementation.</para>
217
218                 <para>Internally, these functions send a single
219                 datagram with the state string as payload to the
220                 <constant>AF_UNIX</constant> socket referenced in the
221                 <varname>$NOTIFY_SOCKET</varname> environment
222                 variable. If the first character of
223                 <varname>$NOTIFY_SOCKET</varname> is <literal>@</literal>, the string is
224                 understood as Linux abstract namespace socket. The
225                 datagram is accompanied by the process credentials of
226                 the sending daemon, using SCM_CREDENTIALS.</para>
227
228                 <para>For details about the algorithms check the
229                 liberally licensed reference implementation sources:
230                 <ulink url="http://cgit.freedesktop.org/systemd/systemd/plain/src/libsystemd-daemon/sd-daemon.c"/>
231                 and <ulink
232                 url="http://cgit.freedesktop.org/systemd/systemd/plain/src/systemd/sd-daemon.h"/></para>
233
234                 <para><function>sd_notify()</function> and
235                 <function>sd_notifyf()</function> are implemented in
236                 the reference implementation's
237                 <filename>sd-daemon.c</filename> and
238                 <filename>sd-daemon.h</filename> files. These
239                 interfaces are available as shared library, which can
240                 be compiled and linked to with the
241                 <constant>libsystemd-daemon</constant> <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
242                 file. Alternatively, applications consuming these APIs
243                 may copy the implementation into their source tree. For
244                 more details about the reference implementation see
245                 <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
246
247                 <para>If the reference implementation is used as
248                 drop-in files and -DDISABLE_SYSTEMD is set during
249                 compilation, these functions will always return 0 and
250                 otherwise become a NOP.</para>
251         </refsect1>
252
253         <refsect1>
254                 <title>Environment</title>
255
256                 <variablelist class='environment-variables'>
257                         <varlistentry>
258                                 <term><varname>$NOTIFY_SOCKET</varname></term>
259
260                                 <listitem><para>Set by the init system
261                                 for supervised processes for status
262                                 and start-up completion
263                                 notification. This environment variable
264                                 specifies the socket
265                                 <function>sd_notify()</function> talks
266                                 to. See above for details.</para></listitem>
267                         </varlistentry>
268                 </variablelist>
269         </refsect1>
270
271         <refsect1>
272                 <title>Examples</title>
273
274                 <example>
275                         <title>Start-up Notification</title>
276
277                         <para>When a daemon finished starting up, it
278                         might issue the following call to notify
279                         the init system:</para>
280
281                         <programlisting>sd_notify(0, "READY=1");</programlisting>
282                 </example>
283
284                 <example>
285                         <title>Extended Start-up Notification</title>
286
287                         <para>A daemon could send the following after
288                         completing initialization:</para>
289
290                         <programlisting>sd_notifyf(0, "READY=1\n"
291               "STATUS=Processing requests...\n"
292               "MAINPID=%lu",
293               (unsigned long) getpid());</programlisting>
294                 </example>
295
296                 <example>
297                         <title>Error Cause Notification</title>
298
299                         <para>A daemon could send the following shortly before exiting, on failure</para>
300
301                         <programlisting>sd_notifyf(0, "STATUS=Failed to start up: %s\n"
302               "ERRNO=%i",
303               strerror(errno),
304               errno);</programlisting>
305                 </example>
306         </refsect1>
307
308         <refsect1>
309                 <title>See Also</title>
310                 <para>
311                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
312                         <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
313                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
314                         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
315                 </para>
316         </refsect1>
317
318 </refentry>