Changing root password in various version of ubuntu [12.04 and above]

There are various ways to change ubuntu 'root' password.But the procedure varies according to the version.
On ubuntu 12.04 it is easy to change the root password.It can be done via terminal.Open it by pressing ctrl+Alt+T.Then type

sudo  -i

passwd

There will appear "Enter New Unix Password:",give it there and done!

But in above versions of ubuntu,i.e.,12.10 and above, sometimes this process becomes useless.It'll give output

passwd:permission denied 

password remains unchanged

To overcome this follow the following process:

1.Select 'recovery mode' from the grub menu

2.Select the option 'root',then a terminal will come in front of you

3.Then type 'mount -o remount,rw /'

4.Then type 'passwd' and give the new password. [or passwd username]

5.Then reboot

Done!
Apply it,for any problem report here.For details follow this link https://help.ubuntu.com/community/LostPassword