opmnctl command hang or does not respond back on linux

I have faced issue on LINUX machine where I was not able to run opmnctl commands such as opmnctl status, opmnctl startall, opmnctl stopall etc.
Each time I run any opmnctl command it gets hang and does not respond back.
On analysis I found that there were orphan opmnctl command which were blocking the new opmnctl commands execution.
Using ps (ps -ef | grep opmn/bin) command, I find out the process ID of the opmnctl commands and killed them using linux kill command. 
On killing the opmnctl processes, the opmnctl commands started working.