Take the 2-minute tour ×
Ask Ubuntu is a question and answer site for Ubuntu users and developers. It's 100% free, no registration required.

This question already has an answer here:

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
share|improve this question

marked as duplicate by Eliah Kagan, Alaa Ali, Warren Hill, Andrea Corbellini, Kevin Bowen Aug 10 at 22:39

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

1  
Are you following a guide? In Ubuntu the root account is disabled and you may need sudo instead –  Braiam Apr 11 at 18:22

5 Answers 5

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  
share|improve this answer

Use sudo your_command in place of su.
ie

sudo apt-get install "program to install"
share|improve this answer

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

  1. Enabling the root account. This can be archived by setting up a password.
  2. Instead of su using 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 rise a security concern, for example, if you use any service exposed to the web.

share|improve this answer

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.

share|improve this answer
1  
After sudo bash you are already root... –  edwin Apr 11 at 19:43
    
@edwin After sudo bash you are running bash as root, but '~' still points to /home/user or wherever your user's home directory is. So you are not quite root. A shortcut for this would be sudo su –  e.thompsy Apr 21 at 12:59
    
For all intends and purposes, you are already root... What's happening is that sudo is preserving some environment variables. Instead of sudo bash it's better to just use sudo -i. –  edwin Apr 21 at 16:50
    
@edwin In some cases these preserved environment variables matter a lot. So I would argue for most intents and purposes you are absolutely right. However, the OP has asked specifically about su to root. I was assuming they knew why they want to do that and that they have a good reason to do it. So I was adding an alternate path to becoming root to the discussion. And here is yet another way: sudo -i then su. But I would totally agree that in most cases just using sudo should be fine. That is what I usually do. Unless I need root. Then I use su. –  e.thompsy Apr 23 at 16:31
    
sudo -i already is enough. Seriously, you just sudo su or sudo -i, this is enough to become root (no need to "su" again)... –  edwin Apr 23 at 17:00

Open root with sudo -s and when it's in this mode type:

passwd

Then, choose password. This password will be for su command.

share|improve this answer

Not the answer you're looking for? Browse other questions tagged or ask your own question.