OK, well, this is not one of those post I’d like to publish, but just counted how many time people asked this question in the last 12 months. I found 32 emails.
I’ll give you the simplest, permanent UNSAFE solution. Use this if you need after finishing you server installation.DO NOT LEAVE ENABLED ON A LIVE RUNNING SERVER.
There are options to enable it temporarily, or set and expire time.
lnrsoft@server:~$ sudo su
[sudo] password for lnrsoft:
root@server:/home/lnrsoft# sudo passwd root
Retype new password:
passwd: password updated successfully