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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 | ||
5 | <!-- | |
6 | This file is part of systemd. | |
7 | ||
8 | Copyright 2010 Lennart Poettering | |
9 | ||
10 | systemd is free software; you can redistribute it and/or modify it | |
11 | under the terms of the GNU General Public License as published by | |
12 | the Free Software Foundation; either version 2 of the License, or | |
13 | (at your option) any later version. | |
14 | ||
15 | systemd is distributed in the hope that it will be useful, but | |
16 | WITHOUT ANY WARRANTY; without even the implied warranty of | |
17 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
18 | General Public License for more details. | |
19 | ||
20 | You should have received a copy of the GNU General Public License | |
21 | along with systemd; If not, see <http://www.gnu.org/licenses/>. | |
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 init system about start-up completion and other daemon status changes</refpurpose> | |
49 | </refnamediv> | |
50 | ||
51 | <refsynopsisdiv> | |
52 | <funcsynopsis> | |
a822cbfa | 53 | <funcsynopsisinfo>#include <systemd/sd-daemon.h></funcsynopsisinfo> |
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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 | |
96d4ce01 | 90 | should contain an newline-separated list of variable |
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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 | |
af62c704 | 107 | value in signalling non-readiness, the |
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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 | |
af62c704 | 118 | is free-form and can be used for |
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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 | ||
436c44a5 | 156 | <para>It is recommended to prefix variable names that |
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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 | |
9f846242 | 169 | <function>sd_notify()</function> but takes a |
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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 | |
af62c704 | 180 | hence no status data could be sent, 0 is returned. If |
f9378423 | 181 | the status was sent these functions return with a |
af62c704 | 182 | positive return value. In order to support both, init |
f9378423 | 183 | systems that implement this scheme and those which |
af62c704 | 184 | don't, it is generally recommended to ignore the return |
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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 | ||
71e6c1cf | 209 | <para>For details about the algorithms check the |
f9378423 | 210 | liberally licensed reference implementation sources: |
8ab49c12 | 211 | <ulink url="http://cgit.freedesktop.org/systemd/plain/src/sd-daemon.c"/> |
f9378423 | 212 | resp. <ulink |
8ab49c12 | 213 | url="http://cgit.freedesktop.org/systemd/plain/src/systemd/sd-daemon.h"/></para> |
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214 | |
215 | <para><function>sd_notify()</function> and | |
216 | <function>sd_notifyf()</function> are implemented in | |
71e6c1cf | 217 | the reference implementation's |
f9378423 | 218 | <filename>sd-daemon.c</filename> and |
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219 | <filename>sd-daemon.h</filename> files. These |
220 | interfaces are available as shared library, which can | |
221 | be compiled and linked to with the | |
222 | <literal>libsystemd-daemon</literal> | |
223 | <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> | |
224 | file. Alternatively, applications consuming these APIs | |
225 | may copy the implementation into their source tree. For | |
f9378423 | 226 | more details about the reference implementation see |
71e6c1cf | 227 | <citerefentry><refentrytitle>sd_daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para> |
f9378423 | 228 | |
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229 | <para>If the reference implementation is used as |
230 | drop-in files and -DDISABLE_SYSTEMD is set during | |
231 | compilation these functions will always return 0 and | |
232 | otherwise become a NOP.</para> | |
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233 | </refsect1> |
234 | ||
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235 | <refsect1> |
236 | <title>Environment</title> | |
237 | ||
238 | <variablelist> | |
239 | <varlistentry> | |
240 | <term><varname>$NOTIFY_SOCKET</varname></term> | |
241 | ||
242 | <listitem><para>Set by the init system | |
243 | for supervised processes for status | |
244 | and start-up completion | |
245 | notification. This environment variable | |
246 | specifies the socket | |
247 | <function>sd_notify()</function> talks | |
248 | to. See above for details.</para></listitem> | |
249 | </varlistentry> | |
250 | </variablelist> | |
251 | </refsect1> | |
252 | ||
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253 | <refsect1> |
254 | <title>Examples</title> | |
255 | ||
256 | <example> | |
257 | <title>Start-up Notification</title> | |
258 | ||
259 | <para>When a daemon finished starting up, it | |
ad678a06 | 260 | might issue the following call to notify |
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261 | the init system:</para> |
262 | ||
263 | <programlisting>sd_notify(0, "READY=1");</programlisting> | |
264 | </example> | |
265 | ||
266 | <example> | |
267 | <title>Extended Start-up Notification</title> | |
268 | ||
269 | <para>A daemon could send the following after | |
270 | completing initialization:</para> | |
271 | ||
272 | <programlisting>sd_notifyf(0, "READY=1\n" | |
273 | "STATUS=Processing requests...\n" | |
274 | "MAINPID=%lu", | |
275 | (unsigned long) getpid());</programlisting> | |
276 | </example> | |
277 | ||
278 | <example> | |
279 | <title>Error Cause Notification</title> | |
280 | ||
281 | <para>A daemon could send the following shortly before exiting, on failure</para> | |
282 | ||
283 | <programlisting>sd_notifyf(0, "STATUS=Failed to start up: %s\n" | |
284 | "ERRNO=%i", | |
285 | strerror(errno), | |
286 | errno);</programlisting> | |
287 | </example> | |
288 | </refsect1> | |
289 | ||
290 | <refsect1> | |
291 | <title>See Also</title> | |
292 | <para> | |
160cd5c9 | 293 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, |
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294 | <citerefentry><refentrytitle>sd_daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>, |
295 | <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>, | |
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296 | <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry> |
297 | </para> | |
298 | </refsect1> | |
299 | ||
300 | </refentry> |