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I have installed ubuntu 11.10 with no problem. But after login as a normal user, I am unable to switch to super user(using "su" command). Its showing "Authentication failure" plz help me..

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marked as duplicate by Eliah Kagan, Alaa Ali, Tim, Warren Hill, Andrea Corbellini Aug 10 '14 at 18:41

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.

In Ubuntu and other Debian-based systems, by default root user has no password set, so it is impossible to log in directly as root or to become root by using su command.

Instead, Ubuntu uses sudo command which allows much more flexible management of permissions - users can perform administrative tasks without knowing root password.

While it is possible to give root user a password, it is not necessary and not recommended.

You can see my answer to this question for more details.

In short, when you need to get root console, you type

sudo su

and then enter your own password. More often, if you want to run a single command as superuser, you just type

sudo command

and, again, enter your own password

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Thanks for your precious solution. – Santosh Parashetti Mar 6 '12 at 4:38

Open the terminal and type the following command:

sudo su
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Thanks, I wil try using sudo su – Santosh Parashetti Mar 6 '12 at 4:39
sudo su

in a terminal, after you type your login password, will turn you root. After this, you can give the command


which will allow you to give a new password for root (this will not alter your login password). This is the password that you will type every time you use the


command, because it will be taken as it is the super user's password.

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Giving root a password is not a normal or recommended practice in Ubuntu. Instead of showing how to shoot himself in the foot to a user who clearly does not understand how things work in Ubuntu, you could've explained how to do it properly. – Sergey Mar 3 '12 at 9:29

only if its a fresh instillation or you never used the su commend before after you install ubuntu . then you have to to give the root a password.

  1. sudo passwd root

then type the password you want.

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You do not have to give root a password in Ubuntu, it's not a normal or recommended practice. Using sudo is preferred – Sergey Mar 3 '12 at 9:25
its truth but he asked about the su command and it will never work because the root user is not enabled by default in Ubuntu. – Fathy Mar 3 '12 at 9:41

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