sd_notify, sd_notifyf — Notify service manager about start-up completion and other service 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() 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 considered
well-known:
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
configuration.
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:
"BUSERROR=org.freedesktop.DBus.Error.TimedOut"
The main pid of the
service, in case the service manager 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 information how to enable this
functionality and
sd_watchdog_enabled(3)
for the details of how the service can
check if the the watchdog is enabled.
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 service 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 service, using SCM_CREDENTIALS.
$NOTIFY_SOCKET¶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:
sd_notify(0, "READY=1");
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);