Read man sshd_config for more details, but you can use the AllowUsers directive in /etc/ssh/sshd_config to limit the set of users who can login. e.g. AllowUsers boris would mean that only the boris user could login via ssh.
● Do you really want to allow logins without a password? If so, try passwd -d root (see warnings below) ● Do you really want to have an empty password? echo root: | chpasswd or, if that is rejected, echo “root:$(mkpasswd -s </dev/null)” | chpasswd -e (see warnings below) ● For those coming here in … Read more
You could also use chpasswd: echo username:new_password | chpasswd so, you change password for user username to new_password.