Red Hat Enterprise Linux Reset Password

Was a nightmare, lost root password...

But quite easy to change it to a new password, just boot to single user mode.
1. During boot up process, when the GRUB menu appeared, press any key.
2. Select the 2nd line and press e
3. Change the word ro  to  rw
4. Add word init=/bin/bash to the last part of the command
     something like: kernel /vmlinuz-2.6.15-122-534 root=/dev/mapper/Ubuntu-root quite rw init=/bin/bash
5. Press ESC, and press 'b' to boot.
6. Once you are in bash mode, just type passwd

Happy!!!

Update: if you got error such "passwd: Authentication token lock busy"
type mount -o remount,rw /
And run passwd again