1- If OS is installed and we have access to OS it can be done using IPMItool or racadm

2- Rebooting the server and configure user/password for Drac in BIOS

3- Boot the server to OMSA live CD and use the IPMItool/racadm/OMSA

4 – Install CentOS on server from CD/DVD

 Methods 2,3 and 4 need physical access to server.

Method 1 can be done remotely if we can login to the OS remotely.

Otherwise if it is Linux and we don’t have password we need physical access for password recovery.