SD_NOTIFY(3)sd_notifySD_NOTIFY(3)NAME
sd_notify, sd_notifyf - Notify init system about start-up completion
and other daemon status changes
SYNOPSIS
#include <systemd/sd-daemon.h>
int sd_notify(int unset_environment, const char *state);
int sd_notifyf(int unset_environment, const char *format, ...);
DESCRIPTIONsd_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
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 an 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:
READY=1
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 signalling non-readiness, the only value daemons should
send is "READY=1".
STATUS=...
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..."
ERRNO=...
If a daemon fails, the errno-style error code, formatted as string.
Example: "ERRNO=2" for ENOENT.
BUSERROR=...
If a daemon fails, the D-Bus error-style error code. Example:
"BUSERROR=org.freedesktop.DBus.Error.TimedOut"
MAINPID=...
The main pid of the daemon, in case the init system did not fork
off the process itself. Example: "MAINPID=4711"
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.
RETURN VALUE
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 don't, it is generally recommended to
ignore the return value of this call.
NOTES
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
$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.
For details about the algorithms check the liberally licensed reference
implementation sources:
http://cgit.freedesktop.org/systemd/systemd/plain/src/sd-daemon.c resp.
http://cgit.freedesktop.org/systemd/systemd/plain/src/systemd/sd-daemon.h
sd_notify() and sd_notifyf() are implemented in the reference
implementation's sd-daemon.c and sd-daemon.h files. These interfaces
are available as shared library, which can be compiled and linked to
with the libsystemd-daemon pkg-config(1) file. Alternatively,
applications consuming these APIs may copy the implementation into
their source tree. For more details about the reference implementation
see sd_daemon(7).
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.
ENVIRONMENT
$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.
EXAMPLES
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);
SEE ALSOsystemd(1), sd_daemon(7), daemon(7), systemd.service(5)AUTHOR
Lennart Poettering <lennart@poettering.net>
Developer
systemd 05/23/2012 SD_NOTIFY(3)
