Why does su fail with "authentication error"? [duplicate]

I tried to su to root so I could install lights, but I get an authentication error when I try:

user@host:~$ su
Password: 
su: Authentication failure

Solution 1:

The root account is disabled by default in Ubuntu, so there is no root password, that's why su fails with an authentication error.

Use sudo to become root:

sudo -i  

Solution 2:

If su doesn't work, I do this (in bash):

user@host:~$ sudo bash
root@host:~# su
root@host:/home/user# 

Voila! You are now root!

A shortcut for this would be sudo su. In this case given that you are a member of /etc/sudoers with all privileges, then you would only need your user's password.

Solution 3:

You are getting Authentication failure because you are trying to become root which is disabled by default in all versions of Ubuntu. This can be easily circumvented in two ways:

1. Enabling the root account. This can be achieved by setting up a password.

2. Instead of su use sudo -i or better yet, append to any command sudo in the way of:

   sudo apt-get update
   [sudo] password for braiam:
   

I wouldn't recommend enabling root, since it could raise a security concern, for example, if you use any service exposed to the web.