Originally Posted by xiaotengyi
I mean the root passwd,I forget it
If you cannot login into the machine, even with your own personal account, then boot your system with CD and reset password by modifying /etc/passwd or /etc/shadow.
Else if you've 'sudo' access with your account, and can login into the machine, then you can reset root passwd by becoming root:
~$ sudo su - root
~$ passwd root
~$ sudo passwd root
But mentioned your distro i.e. OS.