I have installed ubuntu and now I want to install flex. It asks for password but when I type my password, it asks me the password for root.
When I enter the password which I had specified during installation, it says, "Your authentication attempt was unsuccessful. Please try again."
Whether the password for root is locked or is it something else? The passwords I entered were correct.
I have also tried
sudo su but it says, "Unable to change to sudoers gid :operation not permitted."
I have tried su also but when I enter the password it says, "Authentication failure".
Please help me out. I thought that maybe this is because the root user is locked by default. If so, how to recover from it? And if something else is the issue then what to do?