sd_notify, sd_notifyf — Notify service manager about start-up completion and other daemon status changes
|const char *state|
|const char *format,|
sd_notify() shall be called
by a daemon to notify the init system about status
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
parameter is non-zero,
will unset the
environment variable before returning (regardless
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
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 init system that daemon startup is finished. This is only used by systemd if the service definition file has Type=notify set. The passed argument is a boolean "1" or "0". Since there is little value in signaling non-readiness, the only value daemons should send is "READY=1".
Passes a single-line status string back to the init system that describes the daemon 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 daemon fails, the errno-style error code, formatted as string. Example: "ERRNO=2" for ENOENT.
If a daemon fails, the D-Bus error-style error code. Example: "BUSERROR=org.freedesktop.DBus.Error.TimedOut"
The main pid of the daemon, in case the init system did not fork off the process itself. Example: "MAINPID=4711"
Tells systemd to
update the watchdog timestamp. This is
the keep-alive ping that services need
to issue in regular intervals if
enabled for it. See
for details. It is recommended to send
this message if the
environment variable has been set for
the service process, in every half the
time interval that is specified in the
It is recommended to prefix variable names that
are not shown in the list above with
X_ to avoid namespace
Note that systemd will accept status data sent
from a daemon 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
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 functions are provided by the reference implementation of APIs for new-style daemons and distributed with the systemd package. The algorithms they implement are simple, and can easily be reimplemented in daemons if it is important to support this interface without using the reference implementation.
Internally, these functions send a single
datagram with the state string as payload to the
AF_UNIX socket referenced in the
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 daemon, using SCM_CREDENTIALS.
For details about the algorithms check the liberally licensed reference implementation sources: http://cgit.freedesktop.org/systemd/systemd/plain/src/libsystemd-daemon/sd-daemon.c and http://cgit.freedesktop.org/systemd/systemd/plain/src/systemd/sd-daemon.h
sd_notifyf() are implemented in
the reference implementation's
sd-daemon.h files. These
interfaces are available as shared library, which can
be compiled and linked to with the
file. Alternatively, applications consuming these APIs
may copy the implementation into their source tree. For
more details about the reference implementation see
If the reference implementation is used as drop-in files and -DDISABLE_SYSTEMD is set during compilation, these functions will always return 0 and otherwise become a NOP.
Set by the init system
for supervised processes for status
and start-up completion
notification. This environment variable
specifies the socket
to. See above for details.
Example 1. Start-up Notification
When a daemon finished starting up, it might issue the following call to notify the init system:
Example 2. Extended Start-up Notification
A daemon 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 daemon could send the following shortly before exiting, on failure
sd_notifyf(0, "STATUS=Failed to start up: %s\n" "ERRNO=%i", strerror(errno), errno);