reset password for root user - ubuntu server 11.04

1. Reboot the machine.
2. Press the ESC key while GRUB is loading to enter the menu.
3. Select ‘recovery mode’ option.
4. Select ‘drop to root shell prompt’.
5. ‘# nano /etc/passwd’ gives you a list of users
6. change any users password with ‘# passwd [username]
(nếu là root chỉ cần gõ passwd)
Nếu gặp lỗi authentication token manipulation error thì thực hiện lệnh dưới trước khi reset password
mount -rw -o remount /

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Also make sure you are mounting the file system read/write.
After immediately selecting 'Drop into root shell prompt' I found the filesystem was mounted read only, which prevents resetting the password.
Choosing the option to remount / as read/write and going back into the root shell prompt enabled the password change.
The command to run prior to changing the password is: mount -rw -o remount /

nguồn:
http://burnz.wordpress.com/2008/09/09/how-to-reset-ubuntu-root-password/

http://askubuntu.com/questions/91188/authentication-token-manipulation-error
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