Forgot user password and disabled root ssh signin Ubuntu 14.04 server

Question

First I need to say that I'm not pro Linux admin but web master trying to configure server. Though I am learning.

I disabled root ssh login in sake of security and then I forgot to save user account password in Keypass.

I can actually log in as user cause I set log in with SSH Auth keys. But I can't go sudo cause I don't know user's password.

But I know root password.

How can I either:

1. Change user's password logged in as user but not knowing its password (though I know root's)
2. Change ssh settings to enable root log in, after which I would be able to change user's password?

Answer 1

Use /bin/su rather than sudo. That uses root's password.