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Name

sd_notify, sd_notifyf — Notify service manager about start-up completion and other service 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,
 ...);
 

Description

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:

READY=1

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).

RELOADING=1

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.

STOPPING=1

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.

STATUS=...

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..."

ERRNO=...

If a service fails, the errno-style error code, formatted as string. Example: "ERRNO=2" for ENOENT.

BUSERROR=...

If a service fails, the D-Bus error-style error code. Example: "BUSERROR=org.freedesktop.DBus.Error.TimedOut"

MAINPID=...

The main pid of the service, in case the service manager 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 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.

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 do not, it is generally recommended to ignore the return value of this call.

Notes

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.

Environment

$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.

Examples

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);

See Also

systemd(1), sd-daemon(3), daemon(7), systemd.service(5), sd_watchdog_enabled(3)