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

    原文轉自：http://www.ltesting.net