sd_notify, sd_notifyf, sd_pid_notify, sd_pid_notifyf, sd_pid_notify_with_fds — Notify service manager about start-up completion and other service status changes
|const char *state|
|const char *format,|
|const char *state|
|const char *format,|
|const char *state,|
|const int *fds,|
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.
unset_environment parameter is
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.
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 considered
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=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 "
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
If a service fails, the errno-style error
code, formatted as string. Example: "
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.
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
for information how to enable this functionality and
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 be passed
again using the usual file descriptor passing logic on the
next invocation of the service (see
This is useful for implementing service restart schemes where
services serialize their state to
push their file descriptors to the system manager, and are
then restarted, retrieving their state again via socket
/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
for details. 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
It is recommended to prefix variable names that are not
listed above with
X_ to avoid namespace
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
sd_notifyf() is similar to
sd_notify() but takes a
printf()-like format string plus
sd_pid_notifyf() are similar to
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_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
no file descriptors are passed. Note that sending file descriptors
to the service manager on messages that do not expect them (i.e.
FDSTORE=1") they are immediately closed
On failure, these calls return a negative errno-style error
$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
Internally, these functions send a single datagram with the
state string as payload to the
referenced in the
variable. If the first character of
$NOTIFY_SOCKET is "
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
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:
sd_notifyf(0, "READY=1\n" "STATUS=Processing requests...\n" "MAINPID=%lu", (unsigned long) getpid());
Example 3. Error Cause Notification
A service could send the following shortly before exiting, on failure:
sd_notifyf(0, "STATUS=Failed to start up: %s\n" "ERRNO=%i", strerror(errno), errno);
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", &fd, 1);