sd_notify, sd_notifyf — Notify service manager about start-up completion and other daemon status changes
#include <systemd/sd-daemon.h>
int sd_notify( | int unset_environment, |
const char *state) ; |
int sd_notifyf( | int unset_environment, |
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
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 considered
well-known:
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
WatchdogSec=
is
enabled for it. See
systemd.service(5)
for details. It is recommended to send
this message if the
$WATCHDOG_PID
environment variable has been set to
the PID of the service process, in
every half the time interval that is
specified in the
$WATCHDOG_USEC
environment variable. See
sd_watchdog_enabled(3)
for details.
It is recommended to prefix variable names that
are not shown in the list above with
X_
to avoid namespace
clashes.
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
systemd.service(5)
for details.
sd_notifyf()
is similar to
sd_notify()
but takes a
printf()
-like format string plus
arguments.
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.
Internally, 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 daemon, using SCM_CREDENTIALS.
$NOTIFY_SOCKET
¶Set by the init system
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 daemon finished starting up, it might issue the following call to notify the init system:
sd_notify(0, "READY=1");
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);