how to solve when forgetting root password

grub: put 'e' in grub start menu,
         select the line begin with 'kernel', put 'e'
         add ' 1' or ' single' at end, return
         put 'b' to reboot
         when startup finished, use passwd to change root's password
         reboot

lilo:    put 'linux single' in start menu to enter single user mode to change password

原文转自：http://www.ltesting.net