Question

I have a java process daemonized using daemon command (RHEL 6.2). I’m using following line to start the process and the line below to stop it:

daemon --command "/opt/my-service" --respawn --name=my-service --verbose
daemon --stop --name=my-service --verbose  

Things work until I’ll try to restart my process using stop/start approach:

daemon --stop --name=my-service --verbose
daemon --command "/opt/my-service" --respawn --name=my-service --verbose

It the process is running before the above command is executed, then existing process will be stopped but then new one will not be created. Instead, following line will be logged to the /var/log/messages:

Oct 27 07:59:46 myhostname my-service: my-service: fatal: failed to become a daemon: Resource temporarily unavailable

which as far as I understand means that we tried to acquire lock on the pid file but another process was holding the lock on it. Or in the other words: the original process was still running.

What is interesting it can not be reproduced by i.e. following command:

daemon --command "sleep 30s" --respawn --name=sleeper --verbose
daemon --stop --name=sleeper --verbose
daemon --command "sleep 30s" --respawn --name=sleeper --verbose

then there must be something in my process which causes/exploits asynchronous nature of --stop.

How can I make --stop blocking?

Answer 1

This might help:

while true; do
  daemon --name=my-service --running --verbose | grep not
  [ $? -eq 0 ] && exit
  sleep 1
done

Description as p-code:
forever {
check if daemon --name=my-service --running --verbose returns some thing containing the word not
if yes, exit
otherwise sleep a second
}