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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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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 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 of
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_PID</varname>
168                                 environment variable has been set to
169                                 the PID of the service process, in
170                                 every half the time interval that is
171                                 specified in the
172                                 <varname>$WATCHDOG_USEC</varname>
173                                 environment variable. See
174                                 <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
175                                 for details.</para></listitem>
176                         </varlistentry>
177                 </variablelist>
178
179                 <para>It is recommended to prefix variable names that
180                 are not shown in the list above with
181                 <varname>X_</varname> to avoid namespace
182                 clashes.</para>
183
184                 <para>Note that systemd will accept status data sent
185                 from a daemon only if the
186                 <varname>NotifyAccess=</varname> option is correctly
187                 set in the service definition file. See
188                 <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
189                 for details.</para>
190
191                 <para><function>sd_notifyf()</function> is similar to
192                 <function>sd_notify()</function> but takes a
193                 <function>printf()</function>-like format string plus
194                 arguments.</para>
195         </refsect1>
196
197         <refsect1>
198                 <title>Return Value</title>
199
200                 <para>On failure, these calls return a negative
201                 errno-style error code. If
202                 <varname>$NOTIFY_SOCKET</varname> was not set and
203                 hence no status data could be sent, 0 is returned. If
204                 the status was sent, these functions return with a
205                 positive return value. In order to support both, init
206                 systems that implement this scheme and those which
207                 do not, it is generally recommended to ignore the return
208                 value of this call.</para>
209         </refsect1>
210
211         <refsect1>
212                 <title>Notes</title>
213
214                 <para>These functions are provided by the reference
215                 implementation of APIs for new-style daemons and
216                 distributed with the systemd package. The algorithms
217                 they implement are simple, and can easily be
218                 reimplemented in daemons if it is important to support
219                 this interface without using the reference
220                 implementation.</para>
221
222                 <para>Internally, these functions send a single
223                 datagram with the state string as payload to the
224                 <constant>AF_UNIX</constant> socket referenced in the
225                 <varname>$NOTIFY_SOCKET</varname> environment
226                 variable. If the first character of
227                 <varname>$NOTIFY_SOCKET</varname> is <literal>@</literal>, the string is
228                 understood as Linux abstract namespace socket. The
229                 datagram is accompanied by the process credentials of
230                 the sending daemon, using SCM_CREDENTIALS.</para>
231
232                 <para>For details about the algorithms check the
233                 liberally licensed reference implementation sources:
234                 <ulink url="http://cgit.freedesktop.org/systemd/systemd/plain/src/libsystemd-daemon/sd-daemon.c"/>
235                 and <ulink
236                 url="http://cgit.freedesktop.org/systemd/systemd/plain/src/systemd/sd-daemon.h"/></para>
237
238                 <para><function>sd_notify()</function> and
239                 <function>sd_notifyf()</function> are implemented in
240                 the reference implementation's
241                 <filename>sd-daemon.c</filename> and
242                 <filename>sd-daemon.h</filename> files. These
243                 interfaces are available as a shared library, which can
244                 be compiled and linked to with the
245                 <constant>libsystemd-daemon</constant> <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
246                 file. Alternatively, applications consuming these APIs
247                 may copy the implementation into their source tree. For
248                 more details about the reference implementation, see
249                 <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
250
251                 <para>If the reference implementation is used as
252                 drop-in files and -DDISABLE_SYSTEMD is set during
253                 compilation, these functions will always return 0 and
254                 otherwise become a NOP.</para>
255         </refsect1>
256
257         <refsect1>
258                 <title>Environment</title>
259
260                 <variablelist class='environment-variables'>
261                         <varlistentry>
262                                 <term><varname>$NOTIFY_SOCKET</varname></term>
263
264                                 <listitem><para>Set by the init system
265                                 for supervised processes for status
266                                 and start-up completion
267                                 notification. This environment variable
268                                 specifies the socket
269                                 <function>sd_notify()</function> talks
270                                 to. See above for details.</para></listitem>
271                         </varlistentry>
272                 </variablelist>
273         </refsect1>
274
275         <refsect1>
276                 <title>Examples</title>
277
278                 <example>
279                         <title>Start-up Notification</title>
280
281                         <para>When a daemon finished starting up, it
282                         might issue the following call to notify
283                         the init system:</para>
284
285                         <programlisting>sd_notify(0, "READY=1");</programlisting>
286                 </example>
287
288                 <example>
289                         <title>Extended Start-up Notification</title>
290
291                         <para>A daemon could send the following after
292                         completing initialization:</para>
293
294                         <programlisting>sd_notifyf(0, "READY=1\n"
295               "STATUS=Processing requests...\n"
296               "MAINPID=%lu",
297               (unsigned long) getpid());</programlisting>
298                 </example>
299
300                 <example>
301                         <title>Error Cause Notification</title>
302
303                         <para>A daemon could send the following shortly before exiting, on failure</para>
304
305                         <programlisting>sd_notifyf(0, "STATUS=Failed to start up: %s\n"
306               "ERRNO=%i",
307               strerror(errno),
308               errno);</programlisting>
309                 </example>
310         </refsect1>
311
312         <refsect1>
313                 <title>See Also</title>
314                 <para>
315                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
316                         <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
317                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
318                         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
319                         <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
320                 </para>
321         </refsect1>
322
323 </refentry>