Oracle’s lsnrctl start command failed with below error:

TNS-12555: TNS:permission denied
TNS-12560: TNS:protocol adapter error
TNS-00525: Insufficient privilege for operation
Linux Error: 1: Operation not permitted

Solution is to remove files (socket files) under /var/tmp/.oracle; and retry

More Info: These are the socket files created by the lsnrctl when it runs. To find out what files are used by the failing command run :

> strace -aef lsnrctl status LISTENER 

access("/etc/ld.so.preload", R_OK)      = -1 ENOENT (No such file or directory)
access("/etc/listener.ora", F_OK)       = -1 ENOENT (No such file or directory)
access("/u02/app/oracle/product/12.1.0/dbhome_1/network/admin/listener.ora", F_OK) = -1 ENOENT (No such file or directory)
access("/u02/app/oracle/product/12.1.0/dbhome_1/network/admin/sqlnet.ora", F_OK) = -1 ENOENT (No such file or directory)
access("/var/tmp/.oracle", F_OK)        = 0
access("/var/tmp/.oracle/s#9102.2", F_OK) = 0