Ubuntu – Can’t SSH in as root

Best option here is to use sssd for this purpose. I use the AltSecurityIdentities to store the keys and join the servers to the domain using realmd.

Once domain joined, add the following to the /etc/sssd/sssd.conf file under the [domain/] section:

ldap_user_extra_attrs = altSecurityIdentities:altSecurityIdentities

ldap_user_ssh_public_key = altSecurityIdentities

ldap_use_tokengroups = True

and under the [sssd] section add:

services = nss, pam, sudo, ssh

Then to the /etc/ssh/sshd_config add:

AuthorizedKeysCommand /usr/bin/sss_ssh_authorizedkeys

AuthorizedKeysCommandUser root

Restart both services, and you should be able to login using your AD username and the password stored in the AltSecurityIdentities extended attribute in AD.

This may have more reasons. What comes to my mind as first is :

1. You are trying to log as root (Ubuntu does not allow it)
2. On target machine, there is not allowed logging with password (can be configured in /etc/ssh/sshd.conf)
3. You entered wrong IP (of wrong computer)
4. Key authorization is required (Also can be edited in /etc/ssh/sshd.conf)

And as Elias said, if you are using user@ip and not ssh user@ip, it is obvious that it is not working.