уведомлять сервисного менеджера о завершении запуска и других изменениях статуса сервиса (notify service manager about start-up completion and other service status changes)
Окружение (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.