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 - Notify service manager about start-up
8 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
27 sd_notify() may be called by a service to notify the service manager
28 about state changes. It can be used to send arbitrary information,
29 encoded in an environment-block-like string. Most importantly, it can
30 be used for start-up completion notification.
31 If the unset_environment parameter is non-zero, sd_notify() will unset
33 the $NOTIFY_SOCKET environment variable before returning (regardless of
34 whether the function call itself succeeded or not). Further calls to
35 sd_notify() will then fail, but the variable is no longer inherited by
36 child processes.
37 The state parameter should contain a newline-separated list of variable
39 assignments, similar in style to an environment block. A trailing
40 newline is implied if none is specified. The string may contain any
41 kind of variable assignments, but the following shall be considered
42 well-known:
43 READY=1
45 Tells the service manager that service startup is finished, or the
46 service finished loading its configuration. This is only used by
47 systemd if the service definition file has Type=notify set. Since
48 there is little value in signaling non-readiness, the only value
49 services should send is "READY=1" (i.e. "READY=0" is not defined).
50 RELOADING=1
52 Tells the service manager that the service is reloading its
53 configuration. This is useful to allow the service manager to track
54 the service's internal state, and present it to the user. Note that
55 a service that sends this notification must also send a "READY=1"
56 notification when it completed reloading its configuration. Reloads
57 are propagated in the same way as they are when initiated by the
58 user.
59 STOPPING=1
61 Tells the service manager that the service is beginning its
62 shutdown. This is useful to allow the service manager to track the
63 service's internal state, and present it to the user.
64 STATUS=...
66 Passes a single-line UTF-8 status string back to the service
67 manager that describes the service state. This is free-form and can
68 be used for various purposes: general state feedback, fsck-like
69 programs could pass completion percentages and failing programs
70 could pass a human-readable error message. Example:
71 "STATUS=Completed 66% of file system check..."
72 ERRNO=...
74 If a service fails, the errno-style error code, formatted as
75 string. Example: "ERRNO=2" for ENOENT.
76 BUSERROR=...
78 If a service fails, the D-Bus error-style error code. Example:
79 "BUSERROR=org.freedesktop.DBus.Error.TimedOut"
80 MAINPID=...
82 The main process ID (PID) of the service, in case the service
83 manager did not fork off the process itself. Example:
84 "MAINPID=4711"
85 WATCHDOG=1
87 Tells the service manager to update the watchdog timestamp. This is
88 the keep-alive ping that services need to issue in regular
89 intervals if WatchdogSec= is enabled for it. See systemd.service(5)
90 for information how to enable this functionality and
91 sd_watchdog_enabled(3) for the details of how the service can check
92 whether the watchdog is enabled.
93 WATCHDOG=trigger
95 Tells the service manager that the service detected an internal
96 error that should be handled by the configured watchdog options.
97 This will trigger the same behaviour as if WatchdogSec= is enabled
98 and the service did not send "WATCHDOG=1" in time. Note that
99 WatchdogSec= does not need to be enabled for "WATCHDOG=trigger" to
100 trigger the watchdog action. See systemd.service(5) for information
101 about the watchdog behavior.
102 WATCHDOG_USEC=...
104 Reset watchdog_usec value during runtime. Notice that this is not
105 available when using sd_event_set_watchdog() or
106 sd_watchdog_enabled(). Example : "WATCHDOG_USEC=20000000"
107 EXTEND_TIMEOUT_USEC=...
109 Tells the service manager to extend the startup, runtime or
110 shutdown service timeout corresponding the current state. The value
111 specified is a time in microseconds during which the service must
112 send a new message. A service timeout will occur if the message
113 isn't received, but only if the runtime of the current state is
114 beyond the original maximum times of TimeoutStartSec=,
115 RuntimeMaxSec=, and TimeoutStopSec=. See systemd.service(5) for
116 effects on the service timeouts.
117 FDSTORE=1
119 Stores additional file descriptors in the service manager. File
120 descriptors sent this way will be maintained per-service by the
121 service manager and will later be handed back using the usual file
122 descriptor passing logic at the next invocation of the service, see
123 sd_listen_fds(3). This is useful for implementing services that can
124 restart after an explicit request or a crash without losing state.
125 Any open sockets and other file descriptors which should not be
126 closed during the restart may be stored this way. Application state
127 can either be serialized to a file in /run, or better, stored in a
128 memfd_create(2) memory file descriptor. Note that the service
129 manager will accept messages for a service only if its
130 FileDescriptorStoreMax= setting is non-zero (defaults to zero, see
131 systemd.service(5)). If file descriptors sent are pollable (see
132 epoll_ctl(2)), then any EPOLLHUP or EPOLLERR event seen on them
133 will result in their automatic removal from the store. Multiple
134 arrays of file descriptors may be sent in separate messages, in
135 which case the arrays are combined. Note that the service manager
136 removes duplicate (pointing to the same object) file descriptors
137 before passing them to the service. Use sd_pid_notify_with_fds() to
138 send messages with "FDSTORE=1", see below.
139 FDSTOREREMOVE=1
141 Removes file descriptors from the file descriptor store. This field
142 needs to be combined with FDNAME= to specify the name of the file
143 descriptors to remove.
144 FDNAME=...
146 When used in combination with FDSTORE=1, specifies a name for the
147 submitted file descriptors. When used with FDSTOREREMOVE=1,
148 specifies the name for the file descriptors to remove. This name is
149 passed to the service during activation, and may be queried using
150 sd_listen_fds_with_names(3). File descriptors submitted without
151 this field set, will implicitly get the name "stored" assigned.
152 Note that, if multiple file descriptors are submitted at once, the
153 specified name will be assigned to all of them. In order to assign
154 different names to submitted file descriptors, submit them in
155 separate invocations of sd_pid_notify_with_fds(). The name may
156 consist of arbitrary ASCII characters except control characters or
157 ":". It may not be longer than 255 characters. If a submitted name
158 does not follow these restrictions, it is ignored.
159 It is recommended to prefix variable names that are not listed above
161 with X_ to avoid namespace clashes.
162 Note that systemd will accept status data sent from a service only if
164 the NotifyAccess= option is correctly set in the service definition
165 file. See systemd.service(5) for details.
166 Note that sd_notify() notifications may be attributed to units
168 correctly only if either the sending process is still around at the
169 time PID 1 processes the message, or if the sending process is
170 explicitly runtime-tracked by the service manager. The latter is the
171 case if the service manager originally forked off the process, i.e. on
172 all processes that match NotifyAccess=main or NotifyAccess=exec.
173 Conversely, if an auxiliary process of the unit sends an sd_notify()
174 message and immediately exits, the service manager might not be able to
175 properly attribute the message to the unit, and thus will ignore it,
176 even if NotifyAccess=all is set for it.
177 sd_notifyf() is similar to sd_notify() but takes a printf()-like format
179 string plus arguments.
180 sd_pid_notify() and sd_pid_notifyf() are similar to sd_notify() and
182 sd_notifyf() but take a process ID (PID) to use as originating PID for
183 the message as first argument. This is useful to send notification
184 messages on behalf of other processes, provided the appropriate
185 privileges are available. If the PID argument is specified as 0, the
186 process ID of the calling process is used, in which case the calls are
187 fully equivalent to sd_notify() and sd_notifyf().
188 sd_pid_notify_with_fds() is similar to sd_pid_notify() but takes an
190 additional array of file descriptors. These file descriptors are sent
191 along the notification message to the service manager. This is
192 particularly useful for sending "FDSTORE=1" messages, as described
193 above. The additional arguments are a pointer to the file descriptor
194 array plus the number of file descriptors in the array. If the number
195 of file descriptors is passed as 0, the call is fully equivalent to
196 sd_pid_notify(), i.e. no file descriptors are passed. Note that sending
197 file descriptors to the service manager on messages that do not expect
198 them (i.e. without "FDSTORE=1") they are immediately closed on
199 reception.
200
202 On failure, these calls return a negative errno-style error code. If
203 $NOTIFY_SOCKET was not set and hence no status message could be sent, 0
204 is returned. If the status was sent, these functions return a positive
205 value. In order to support both service managers that implement this
206 scheme and those which do not, it is generally recommended to ignore
207 the return value of this call. Note that the return value simply
208 indicates whether the notification message was enqueued properly, it
209 does not reflect whether the message could be processed successfully.
210 Specifically, no error is returned when a file descriptor is attempted
211 to be stored using FDSTORE=1 but the service is not actually configured
212 to permit storing of file descriptors (see above).
213
215 These APIs are implemented as a shared library, which can be compiled
216 and linked to with the libsystemd pkg-config(1) file.
217 These functions send a single datagram with the state string as payload
219 to the AF_UNIX socket referenced in the $NOTIFY_SOCKET environment
220 variable. If the first character of $NOTIFY_SOCKET is "@", the string
221 is understood as Linux abstract namespace socket. The datagram is
222 accompanied by the process credentials of the sending service, using
223 SCM_CREDENTIALS.
224
226 $NOTIFY_SOCKET
227 Set by the service manager for supervised processes for status and
228 start-up completion notification. This environment variable
229 specifies the socket sd_notify() talks to. See above for details.
230
232 Example 1. Start-up Notification
233 When a service finished starting up, it might issue the following call
235 to notify the service manager:
236 sd_notify(0, "READY=1");
238 Example 2. Extended Start-up Notification
240 A service could send the following after completing initialization:
242 sd_notifyf(0, "READY=1\n"
244 "STATUS=Processing requests...\n"
245 "MAINPID=%lu",
246 (unsigned long) getpid());
247 Example 3. Error Cause Notification
249 A service could send the following shortly before exiting, on failure:
251 sd_notifyf(0, "STATUS=Failed to start up: %s\n"
253 "ERRNO=%i",
254 strerror(errno),
255 errno);
256 Example 4. Store a File Descriptor in the Service Manager
258 To store an open file descriptor in the service manager, in order to
260 continue operation after a service restart without losing state, use
261 "FDSTORE=1":
262 sd_pid_notify_with_fds(0, 0, "FDSTORE=1\nFDNAME=foobar", &fd, 1);
264
266 systemd(1), sd-daemon(3), sd_listen_fds(3),
267 sd_listen_fds_with_names(3), sd_watchdog_enabled(3), daemon(7),
268 systemd.service(5)
269systemd 243 SD_NOTIFY(3)