sudo vi /etc/hosts
but it was reset every time when system was rebooted.
The reason being I have installed Cisco AnyConnect VPN client, which keeps a separate copy of the original hosts file, and will restore my hosts file from it each time after reboot.
ls /etc/hosts* => /etc/hosts /etc/hosts.ac /etc/hosts.equiv
So the solution is to update both "/etc/hosts" and "/etc/hosts.ac" to keep them in sync.
Hope this helps you too.