I wanted to change my own password, but instead of using sudo passwd myuser, I used sudo passwd by mistake, and so I set the password for root. Does that mean that my root account is enabled now? I know that it's supposed to be disabled in Ubuntu. What steps should I take to disable it again? It's currently set to the same password as my own user account, and it's kind of redundant, because my user is in the sudoers list anyway.
Yes, the root account is now enabled. You can disable it with
sudo passwd -dl root. See https://help.ubuntu.com/community/RootSudo#Re-disabling_your_root_accountTo change your user's password, just run
passwdinstead ofsudo passwd username.