I need to access root under my Ubuntu 12.04.3 LTS, to accomplish some in-chain commands,  but I had no idea what is/was the password….

pjrfigueiredo@pornrack:~$ sudo wget http://repo.ajenti.org/debian/key -O- | apt-key add -
[sudo] password for pjrfigueiredo: ERROR: This command can only be used by root.

This is how I easily solved it…

sudo passwd

Voilá!

 

pjrfigueiredo@pornrack:~$ sudo passwd 
Enter new UNIX password: 
Retype new UNIX password: 
passwd: password updated successfully
pjrfigueiredo@pornrack:~$ su
Password: 
root@pornrack:/home/pjrfigueiredo# wget http://repo.ajenti.org/debian/key -O- | apt-key add -
--2013-11-01 23:05:56-- http://repo.ajenti.org/debian/key
Resolving repo.ajenti.org (repo.ajenti.org)... 108.161.187.129
Connecting to repo.ajenti.org (repo.ajenti.org)|108.161.187.129|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 1716 (1.7K) [application/octet-stream]
Saving to: `STDOUT'100%[========================================================================================================================================>] 1,716 --.-K/s in 0.002s
2013-11-01 23:05:56 (1.01 MB/s) - written to stdout [1716/1716]

OK