sd_notify() may be called by a service to notify the service manager
about state changes. It can be used to send arbitrary information,
encoded in an environment-block-like string. Most importantly, it can
be used for start-up completion notification.
If the unset_environment parameter is non-zero, sd_notify() will
unset the $NOTIFY_SOCKET environment variable before returning
(regardless of whether the function call itself succeeded or not).
Further calls to sd_notify() will then fail, but the variable is no
longer inherited by child processes.
The state parameter should contain a newline-separated list of
variable assignments, similar in style to an environment block. A
trailing newline is implied if none is specified. The string may
contain any kind of variable assignments, but the following shall be
Tells the service manager that service startup is finished. This
is only used by systemd if the service definition file has
Type=notify set. Since there is little value in signaling
non-readiness, the only value services should send is "READY=1"
(i.e. "READY=0" is not defined).
Tells the service manager that the service is reloading its
configuration. This is useful to allow the service manager to
track the service's internal state, and present it to the user.
Note that a service that sends this notification must also send a
"READY=1" notification when it completed reloading its
Tells the service manager that the service is beginning its
shutdown. This is useful to allow the service manager to track
the service's internal state, and present it to the user.
Passes a single-line UTF-8 status string back to the service
manager that describes the service state. This is free-form and
can be used for various purposes: general state feedback,
fsck-like programs could pass completion percentages and failing
programs could pass a human-readable error message. Example:
"STATUS=Completed 66% of file system check..."
If a service fails, the errno-style error code, formatted as
string. Example: "ERRNO=2" for ENOENT.
If a service fails, the D-Bus error-style error code. Example:
The main process ID (PID) of the service, in case the service
manager did not fork off the process itself. Example:
Tells the service manager to update the watchdog timestamp. This
is the keep-alive ping that services need to issue in regular
intervals if WatchdogSec= is enabled for it. See
systemd.service(5) for information how to enable this
functionality and sd_watchdog_enabled(3) for the details of how
the service can check whether the watchdog is enabled.
Stores additional file descriptors in the service manager. File
descriptors sent this way will be maintained per-service by the
service manager and will be passed again using the usual file
descriptor passing logic on the next invocation of the service,
see sd_listen_fds(3). This is useful for implementing service
restart schemes where services serialize their state to /run,
push their file descriptors to the system manager, and are then
restarted, retrieving their state again via socket passing and
/run. Note that the service manager will accept messages for a
service only if FileDescriptorStoreMax= is set to non-zero for it
(defaults to zero, see systemd.service(5)). File descriptors must
be pollable, see epoll_ctl(2). Multiple arrays of file
descriptors may be sent in separate messages, in which case the
arrays are combined. Note that the service manager removes
duplicate file descriptors before passing them to the service.
Use sd_pid_notify_with_fds() to send messages with "FDSTORE=1",
When used in combination with FDSTORE=1, specifies a name for the
submitted file descriptors. This name is passed to the service
during activation, and may be queried using
sd_listen_fds_with_names(3). File descriptors submitted without
this field set, will implicitly get the name "stored" assigned.
Note that, if multiple file descriptors are submitted at once,
the specified name will be assigned to all of them. In order to
assign different names to submitted file descriptors, submit them
in separate invocations of sd_pid_notify_with_fds(). The name may
consist of any ASCII character, but must not contain control
characters or ":". It may not be longer than 255 characters. If a
submitted name does not follow these restrictions, it is ignored.
Reset watchdog_usec value during runtime. Notice that this is not
available when using sd_event_set_watchdog() or
sd_watchdog_enabled(). Example : "WATCHDOG_USEC=20000000"
It is recommended to prefix variable names that are not listed above
with X_ to avoid namespace clashes.
Note that systemd will accept status data sent from a service only if
the NotifyAccess= option is correctly set in the service definition
file. See systemd.service(5) for details.
Note that sd_notify() notifications may be attributed to units
correctly only if either the sending process is still around at the
time PID 1 processes the message, or if the sending process is
explicitly runtime-tracked by the service manager. The latter is the
case if the service manager originally forked off the process, i.e.
on all processes that match NotifyAccess=main or NotifyAccess=exec.
Conversely, if an auxiliary process of the unit sends an sd_notify()
message and immediately exits, the service manager might not be able
to properly attribute the message to the unit, and thus will ignore
it, even if NotifyAccess=all is set for it.
sd_notifyf() is similar to sd_notify() but takes a printf()-like
format string plus arguments.
sd_pid_notify() and sd_pid_notifyf() are similar to sd_notify() and
sd_notifyf() but take a process ID (PID) to use as originating PID
for the message as first argument. This is useful to send
notification messages on behalf of other processes, provided the
appropriate privileges are available. If the PID argument is
specified as 0, the process ID of the calling process is used, in
which case the calls are fully equivalent to sd_notify() and
sd_pid_notify_with_fds() is similar to sd_pid_notify() but takes an
additional array of file descriptors. These file descriptors are sent
along the notification message to the service manager. This is
particularly useful for sending "FDSTORE=1" messages, as described
above. The additional arguments are a pointer to the file descriptor
array plus the number of file descriptors in the array. If the number
of file descriptors is passed as 0, the call is fully equivalent to
sd_pid_notify(), i.e. no file descriptors are passed. Note that
sending file descriptors to the service manager on messages that do
not expect them (i.e. without "FDSTORE=1") they are immediately
closed on reception.
On failure, these calls return a negative errno-style error code. If
$NOTIFY_SOCKET was not set and hence no status data could be sent, 0
is returned. If the status was sent, these functions return with a
positive return value. In order to support both, init systems that
implement this scheme and those which do not, it is generally
recommended to ignore the return value of this call.
These APIs are implemented as a shared library, which can be compiled
and linked to with the libsystemd pkg-config(1) file.
These functions send a single datagram with the state string as
payload to the AF_UNIX socket referenced in the $NOTIFY_SOCKET
environment variable. If the first character of $NOTIFY_SOCKET is
"@", the string is understood as Linux abstract namespace socket. The
datagram is accompanied by the process credentials of the sending
service, using SCM_CREDENTIALS.
Set by the service manager for supervised processes for status
and start-up completion notification. This environment variable
specifies the socket sd_notify() talks to. See above for details.
Example 1. Start-up Notification
When a service finished starting up, it might issue the following
call to notify the service manager:
Example 2. Extended Start-up Notification
A service could send the following after completing initialization:
(unsigned long) getpid());
Example 3. Error Cause Notification
A service could send the following shortly before exiting, on
sd_notifyf(0, "STATUS=Failed to start up: %s\n"
Example 4. Store a File Descriptor in the Service Manager
To store an open file descriptor in the service manager, in order to
continue operation after a service restart without losing state, use
sd_pid_notify_with_fds(0, 0, "FDSTORE=1\nFDNAME=foobar", &fd, 1);
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systemd 233 SD_NOTIFY(3)