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Michael
Asked: 2014-04-12 10:13:17 +0800 CST

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

  • 772

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
su

5 Answers

  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
    • 223

  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.

    • 22

  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.

    • 12

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

    passwd

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

    • 10

  5. Use sudo your_command in place of su.
    ie

    sudo apt-get install "program to install"
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