In this post, I'll tell you, how to create new user in Ubuntu 14.04 and how you disable user password login.

New user

Create new user, in my e.g. it's example-user. Set strong password, and fill fields.

$ sudo adduser example-user

SSH key login

Now you're created new user. In second step, we have to generate new ssh key (if you don't already had it).

$ ssh-keygen

And use default value for:

Generating public/private rsa key pair.
Enter file in which to save the key (~/.ssh/id_rsa):

Next we need to copy our ssh key into example-user's authorizies keys file (~/.ssh/authorized_keys).

$ ssh-copy-id example-user@localhost

If you got next lines, you're permit login to example-user by ssh key.

Number of key(s) added: 1

Now try logging into the machine, with:   "ssh 'example-user@localhost'"
and check to make sure that only the key(s) you wanted were added.

Disable user password login

It mean that, you're not longer need password to login example-user. So if we don't any more need password to login our new user, we could disable password login to that user.

$ sudo usermod -L example-user