And so I was playing around with configuration and then I tried to restart shibd process. I kept getting "listener failed to initialize".
Newbie to Shibboleth. Took me a while to find out that the process was killed, but the pid and .sock files are not removed.
Once both files are removed from /var/run/shibboleth directory, the shibd process is able to start successfully!
PS: By the way, the proper way to restart shibd process is:
[root@cdemo shibboleth]# /etc/init.d/shibd restart
Stopping shibd: [ OK ]
Starting shibd: [ OK ]