1SD_NOTIFY(3) sd_notify SD_NOTIFY(3)
2
6 sd_notify, sd_notifyf, sd_pid_notify, sd_pid_notifyf,
7 sd_pid_notify_with_fds, sd_notify_barrier - Notify service manager
8 about start-up completion and other service status changes
9
11 #include <systemd/sd-daemon.h>
12 int sd_notify(int unset_environment, const char *state);
14 int sd_notifyf(int unset_environment, const char *format, ...);
16 int sd_pid_notify(pid_t pid, int unset_environment, const char *state);
18 int sd_pid_notifyf(pid_t pid, int unset_environment,
20 const char *format, ...);
21 int sd_pid_notify_with_fds(pid_t pid, int unset_environment,
23 const char *state, const int *fds,
24 unsigned n_fds);
25 int sd_notify_barrier(int unset_environment, uint64_t timeout);
27
29 sd_notify() may be called by a service to notify the service manager
30 about state changes. It can be used to send arbitrary information,
31 encoded in an environment-block-like string. Most importantly, it can
32 be used for start-up completion notification.
33 If the unset_environment parameter is non-zero, sd_notify() will unset
35 the $NOTIFY_SOCKET environment variable before returning (regardless of
36 whether the function call itself succeeded or not). Further calls to
37 sd_notify() will then fail, but the variable is no longer inherited by
38 child processes.
39 The state parameter should contain a newline-separated list of variable
41 assignments, similar in style to an environment block. A trailing
42 newline is implied if none is specified. The string may contain any
43 kind of variable assignments, but the following shall be considered
44 well-known:
45 READY=1
47 Tells the service manager that service startup is finished, or the
48 service finished loading its configuration. This is only used by
49 systemd if the service definition file has Type=notify set. Since
50 there is little value in signaling non-readiness, the only value
51 services should send is "READY=1" (i.e. "READY=0" is not defined).
52 RELOADING=1
54 Tells the service manager that the service is reloading its
55 configuration. This is useful to allow the service manager to track
56 the service's internal state, and present it to the user. Note that
57 a service that sends this notification must also send a "READY=1"
58 notification when it completed reloading its configuration. Reloads
59 are propagated in the same way as they are when initiated by the
60 user.
61 STOPPING=1
63 Tells the service manager that the service is beginning its
64 shutdown. This is useful to allow the service manager to track the
65 service's internal state, and present it to the user.
66 STATUS=...
68 Passes a single-line UTF-8 status string back to the service
69 manager that describes the service state. This is free-form and can
70 be used for various purposes: general state feedback, fsck-like
71 programs could pass completion percentages and failing programs
72 could pass a human-readable error message. Example:
73 "STATUS=Completed 66% of file system check..."
74 ERRNO=...
76 If a service fails, the errno-style error code, formatted as
77 string. Example: "ERRNO=2" for ENOENT.
78 BUSERROR=...
80 If a service fails, the D-Bus error-style error code. Example:
81 "BUSERROR=org.freedesktop.DBus.Error.TimedOut"
82 MAINPID=...
84 The main process ID (PID) of the service, in case the service
85 manager did not fork off the process itself. Example:
86 "MAINPID=4711"
87 WATCHDOG=1
89 Tells the service manager to update the watchdog timestamp. This is
90 the keep-alive ping that services need to issue in regular
91 intervals if WatchdogSec= is enabled for it. See systemd.service(5)
92 for information how to enable this functionality and
93 sd_watchdog_enabled(3) for the details of how the service can check
94 whether the watchdog is enabled.
95 WATCHDOG=trigger
97 Tells the service manager that the service detected an internal
98 error that should be handled by the configured watchdog options.
99 This will trigger the same behaviour as if WatchdogSec= is enabled
100 and the service did not send "WATCHDOG=1" in time. Note that
101 WatchdogSec= does not need to be enabled for "WATCHDOG=trigger" to
102 trigger the watchdog action. See systemd.service(5) for information
103 about the watchdog behavior.
104 WATCHDOG_USEC=...
106 Reset watchdog_usec value during runtime. Notice that this is not
107 available when using sd_event_set_watchdog() or
108 sd_watchdog_enabled(). Example : "WATCHDOG_USEC=20000000"
109 EXTEND_TIMEOUT_USEC=...
111 Tells the service manager to extend the startup, runtime or
112 shutdown service timeout corresponding the current state. The value
113 specified is a time in microseconds during which the service must
114 send a new message. A service timeout will occur if the message
115 isn't received, but only if the runtime of the current state is
116 beyond the original maximum times of TimeoutStartSec=,
117 RuntimeMaxSec=, and TimeoutStopSec=. See systemd.service(5) for
118 effects on the service timeouts.
119 FDSTORE=1
121 Stores additional file descriptors in the service manager. File
122 descriptors sent this way will be maintained per-service by the
123 service manager and will later be handed back using the usual file
124 descriptor passing logic at the next invocation of the service
125 (e.g. when it is restarted), see sd_listen_fds(3). This is useful
126 for implementing services that can restart after an explicit
127 request or a crash without losing state. Any open sockets and other
128 file descriptors which should not be closed during the restart may
129 be stored this way. Application state can either be serialized to a
130 file in /run/, or better, stored in a memfd_create(2) memory file
131 descriptor. Note that the service manager will accept messages for
132 a service only if its FileDescriptorStoreMax= setting is non-zero
133 (defaults to zero, see systemd.service(5)). If FDPOLL=0 is not set
134 and the file descriptors sent are pollable (see epoll_ctl(2)), then
135 any EPOLLHUP or EPOLLERR event seen on them will result in their
136 automatic removal from the store. Multiple arrays of file
137 descriptors may be sent in separate messages, in which case the
138 arrays are combined. Note that the service manager removes
139 duplicate (pointing to the same object) file descriptors before
140 passing them to the service. When a service is stopped, its file
141 descriptor store is discarded and all file descriptors in it are
142 closed. Use sd_pid_notify_with_fds() to send messages with
143 "FDSTORE=1", see below.
144 FDSTOREREMOVE=1
146 Removes file descriptors from the file descriptor store. This field
147 needs to be combined with FDNAME= to specify the name of the file
148 descriptors to remove.
149 FDNAME=...
151 When used in combination with FDSTORE=1, specifies a name for the
152 submitted file descriptors. When used with FDSTOREREMOVE=1,
153 specifies the name for the file descriptors to remove. This name is
154 passed to the service during activation, and may be queried using
155 sd_listen_fds_with_names(3). File descriptors submitted without
156 this field set, will implicitly get the name "stored" assigned.
157 Note that, if multiple file descriptors are submitted at once, the
158 specified name will be assigned to all of them. In order to assign
159 different names to submitted file descriptors, submit them in
160 separate invocations of sd_pid_notify_with_fds(). The name may
161 consist of arbitrary ASCII characters except control characters or
162 ":". It may not be longer than 255 characters. If a submitted name
163 does not follow these restrictions, it is ignored.
164 FDPOLL=0
166 When used in combination with FDSTORE=1, disables polling of the
167 stored file descriptors regardless of whether or not they are
168 pollable. As this option disables automatic cleanup of the stored
169 file descriptors on EPOLLERR and EPOLLHUP, care must be taken to
170 ensure proper manual cleanup. Use of this option is not generally
171 recommended except for when automatic cleanup has unwanted behavior
172 such as prematurely discarding file descriptors from the store.
173 BARRIER=1
175 Tells the service manager that the client is explicitly requesting
176 synchronization by means of closing the file descriptor sent with
177 this command. The service manager guarantees that the processing of
178 a BARRIER=1 command will only happen after all previous
179 notification messages sent before this command have been processed.
180 Hence, this command accompanied with a single file descriptor can
181 be used to synchronize against reception of all previous status
182 messages. Note that this command cannot be mixed with other
183 notifications, and has to be sent in a separate message to the
184 service manager, otherwise all assignments will be ignored. Note
185 that sending 0 or more than 1 file descriptor with this command is
186 a violation of the protocol.
187 It is recommended to prefix variable names that are not listed above
189 with X_ to avoid namespace clashes.
190 Note that systemd will accept status data sent from a service only if
192 the NotifyAccess= option is correctly set in the service definition
193 file. See systemd.service(5) for details.
194 Note that sd_notify() notifications may be attributed to units
196 correctly only if either the sending process is still around at the
197 time PID 1 processes the message, or if the sending process is
198 explicitly runtime-tracked by the service manager. The latter is the
199 case if the service manager originally forked off the process, i.e. on
200 all processes that match NotifyAccess=main or NotifyAccess=exec.
201 Conversely, if an auxiliary process of the unit sends an sd_notify()
202 message and immediately exits, the service manager might not be able to
203 properly attribute the message to the unit, and thus will ignore it,
204 even if NotifyAccess=all is set for it.
205 Hence, to eliminate all race conditions involving lookup of the
207 client's unit and attribution of notifications to units correctly,
208 sd_notify_barrier() may be used. This call acts as a synchronization
209 point and ensures all notifications sent before this call have been
210 picked up by the service manager when it returns successfully. Use of
211 sd_notify_barrier() is needed for clients which are not invoked by the
212 service manager, otherwise this synchronization mechanism is
213 unnecessary for attribution of notifications to the unit.
214 sd_notifyf() is similar to sd_notify() but takes a printf()-like format
216 string plus arguments.
217 sd_pid_notify() and sd_pid_notifyf() are similar to sd_notify() and
219 sd_notifyf() but take a process ID (PID) to use as originating PID for
220 the message as first argument. This is useful to send notification
221 messages on behalf of other processes, provided the appropriate
222 privileges are available. If the PID argument is specified as 0, the
223 process ID of the calling process is used, in which case the calls are
224 fully equivalent to sd_notify() and sd_notifyf().
225 sd_pid_notify_with_fds() is similar to sd_pid_notify() but takes an
227 additional array of file descriptors. These file descriptors are sent
228 along the notification message to the service manager. This is
229 particularly useful for sending "FDSTORE=1" messages, as described
230 above. The additional arguments are a pointer to the file descriptor
231 array plus the number of file descriptors in the array. If the number
232 of file descriptors is passed as 0, the call is fully equivalent to
233 sd_pid_notify(), i.e. no file descriptors are passed. Note that sending
234 file descriptors to the service manager on messages that do not expect
235 them (i.e. without "FDSTORE=1") they are immediately closed on
236 reception.
237 sd_notify_barrier() allows the caller to synchronize against reception
239 of previously sent notification messages and uses the BARRIER=1
240 command. It takes a relative timeout value in microseconds which is
241 passed to ppoll(2). A value of UINT64_MAX is interpreted as infinite
242 timeout.
243
245 On failure, these calls return a negative errno-style error code. If
246 $NOTIFY_SOCKET was not set and hence no status message could be sent, 0
247 is returned. If the status was sent, these functions return a positive
248 value. In order to support both service managers that implement this
249 scheme and those which do not, it is generally recommended to ignore
250 the return value of this call. Note that the return value simply
251 indicates whether the notification message was enqueued properly, it
252 does not reflect whether the message could be processed successfully.
253 Specifically, no error is returned when a file descriptor is attempted
254 to be stored using FDSTORE=1 but the service is not actually configured
255 to permit storing of file descriptors (see above).
256
258 These APIs are implemented as a shared library, which can be compiled
259 and linked to with the libsystemd pkg-config(1) file.
260 These functions send a single datagram with the state string as payload
262 to the AF_UNIX socket referenced in the $NOTIFY_SOCKET environment
263 variable. If the first character of $NOTIFY_SOCKET is "@", the string
264 is understood as Linux abstract namespace socket. The datagram is
265 accompanied by the process credentials of the sending service, using
266 SCM_CREDENTIALS.
267
269 $NOTIFY_SOCKET
270 Set by the service manager for supervised processes for status and
271 start-up completion notification. This environment variable
272 specifies the socket sd_notify() talks to. See above for details.
273
275 Example 1. Start-up Notification
276 When a service finished starting up, it might issue the following call
278 to notify the service manager:
279 sd_notify(0, "READY=1");
281 Example 2. Extended Start-up Notification
283 A service could send the following after completing initialization:
285 sd_notifyf(0, "READY=1\n"
287 "STATUS=Processing requests...\n"
288 "MAINPID=%lu",
289 (unsigned long) getpid());
290 Example 3. Error Cause Notification
292 A service could send the following shortly before exiting, on failure:
294 sd_notifyf(0, "STATUS=Failed to start up: %s\n"
296 "ERRNO=%i",
297 strerror(errno),
298 errno);
299 Example 4. Store a File Descriptor in the Service Manager
301 To store an open file descriptor in the service manager, in order to
303 continue operation after a service restart without losing state, use
304 "FDSTORE=1":
305 sd_pid_notify_with_fds(0, 0, "FDSTORE=1\nFDNAME=foobar", &fd, 1);
307 Example 5. Eliminating race conditions
309 When the client sending the notifications is not spawned by the service
311 manager, it may exit too quickly and the service manager may fail to
312 attribute them correctly to the unit. To prevent such races, use
313 sd_notify_barrier() to synchronize against reception of all
314 notifications sent before this call is made.
315 sd_notify(0, "READY=1");
317 /* set timeout to 5 seconds */
318 sd_notify_barrier(0, 5 * 1000000);
319
322 systemd(1), sd-daemon(3), sd_listen_fds(3),
323 sd_listen_fds_with_names(3), sd_watchdog_enabled(3), daemon(7),
324 systemd.service(5)
325systemd 251 SD_NOTIFY(3)