If you forgotten the root password, we can easily recover it but the system requires 2 recycles.
Here is the way I follow
Password recovery is one of the simplest troubleshooting procedure in
AIX. Once you boot from CD, you see a menu with 3 menu items.
In that select the 3rd item
ie., “Start Maintenance Mode for System Recovery” à
“Access a Root Volume Group” ->
“Access this volume group and start a shell”.
This will open a shell prompt. The just use “passwd” command for
setting a new password for root.
Thats it. root password has been changed.
Now you can reboot the machine from rootvg hard disk (normally it should be hdisk0)