Question :
What does the oracle utility “lsnrctl” actually do? For instance, lsnrctl stop actually stops the listener and kills the process id, but does it also remove lock files or set/unset variables?
Answer :
The lsnrctl utility sends commands to the listener process. If one sends the stop command to a listener process, the process shuts down. The listener program does not kill the process, but the process shuts down. If a unix process shuts down its process id will be removed from the process list. All fgiles locked or opened by the process will be closed by the operating system. A process cannot and will not set/unset variables of your environment. Only your current shell can change its (your) variables.
The answer was, check the network interface. eth0 had no IP address assigned to it. Once we assigned the address, the listener worked as expected