How to enable root login ubuntu-15.04-server

                

The root user in Ubuntu is disabled by default because his password is not set. But if you'd like to use root user by some reason, enable it like follows.

Set root password.

root@amir:~$ sudo passwd root

Enter new UNIX password:                    # set root password

Retype new UNIX password:                # confirm

passwd: password updated successfully

root@amir:~$ su -

Password:                           # root password

root@amir:~                       ## just switched             

If you enable root, limit users to switch to root.

root@amir:~# vi /etc/pam.d/su

# line 15: uncomment and add a group that can switch to root

auth   required   pam_wheel.so   group=adm

root@amir:~# usermod -G adm root

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