I am trying to log into a server with a particular account. Let's say I don't know the password for that account. Can I do this using ssh? I am wondering if it is possible to do it in one command, instead of logging in as root and running su.
This doesn't make sense. If you're logged in as root, a plain
su doesn't do anything except start a new shell. Maybe you mean
As far as I know, most Linux installations don't allow root logging in remotely directly. One first has to log in as an ordinary user and su to become root.
You could probably accomplish this if you were willing to write a PAM module which caused entering the root password to make authentication succeed. Not going to be easy, but it would do what you want...