Originally Posted by mq15
1. So if I login as a normal user, would I be able to still use/access applications/data that I installed as root user? specially NS2?
2. Cannot we avoid this error if I need to login as root user?
1. Yes, provided they have executable permissions for all users (rwxr-xr-x). Applications which require root privileges (like Add/Remove Software) will prompt you for root password. If you need to run application from the terminal as root, you can always do su -
and become root.
2. I don't know. Maybe the solution is in the link provided by Alans07.