TNS-12555 / TNS-12560 / TNS-00525 Error listening on: (DESCRIPTION=(ADDRESS=(PROTOCOL=IPC)(KEY=EXTPROC1)))

Problem:LSNRCTL for Linux: Version 10.2.0.1.0 – Production
Copyright (c) 1991, 2005, Oracle. All rights reserved.
Welcome to LSNRCTL, type “help” for information.
LSNRCTL> start
Starting /u01/app/oracle/oracle/product/10.2.0/db_1//bin/tnslsnr: please wait…
TNSLSNR for Linux: Version 10.2.0.2.0 – Production
System parameter file is /u01/app/oracle/oracle/product/10.2.0/db_1/network/admin/listener.ora
Log messages written to /u01/app/oracle/oracle/product/10.2.0/db_1/network/log/listener.log
Error listening on: (DESCRIPTION=(ADDRESS=(PROTOCOL=IPC)(KEY=EXTPROC1)))
TNS-12555: TNS:permission denied
TNS-12560: TNS:protocol adapter error
TNS-00525: Insufficient privilege for operation
Linux Error: 1: Operation not permitted
Listener failed to start. See the error message(s) above…
LSNRCTL>
Cause:
1) Ensure that /tmp/.oracle or /var/tmp/.oracle directory exists.
2) Confirm that the DBA user who is trying to start the listener has adequate read and write permissions on the directory specified above. The permissions
should be 777.
3) If the /tmp directory has reached full capacity, this would cause the listener to fail to write the socket files.

Solution
To implement the solution, please use the following example:

1. cd /var/tmp
2. Check the whether the .oracle directory exists:
cd .oracle
3. If the directory does not exist, request the System Administrator create the directory and set the ownership as root:root with the permissions set to 01777

mkdir /var/tmp/.oracle
chmod 01777 /var/tmp/.oracle
chown root /var/tmp/.oracle
chgrp root /var/tmp/.oracle

4. Next try starting the TNS Listener using the ‘lsnrctl start <listener_name>’ command.