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SD_NOTIFY(3) | sd_notify | SD_NOTIFY(3) |
NAME¶
sd_notify, sd_notifyf - Notify service manager about start-up completion and other daemon status changesSYNOPSIS¶
#include <systemd/sd-daemon.h>
int
sd_notify(int unset_environment,
const char *state);
int
sd_notifyf(int unset_environment,
const char *format, ...);
DESCRIPTION¶
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 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: READY=1Tells 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".
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"
WATCHDOG=1
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_USEC= environment variable has been set for the service
process, in every half the time interval that is specified in the
variable.
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/libsystemd-daemon/sd-daemon.c and 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(3). 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_SOCKETSet 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");
sd_notifyf(0, "READY=1\n" "STATUS=Processing requests...\n" "MAINPID=%lu", (unsigned long) getpid());
sd_notifyf(0, "STATUS=Failed to start up: %s\n" "ERRNO=%i", strerror(errno), errno);
SEE ALSO¶
systemd 204 |