Allow SSH root login on Ubuntu 18.04 Bionic Beaver Linux

Instructions
Set Root Password
By default Ubuntu 18.04 Bionic Beaver installation comes with unset root password. To set root password open up terminal and execute the following linux command. When prompted enter your current user password and new root password:
$ sudo passwd
[sudo] password for linuxconfig:
Enter new UNIX password:
Retype new UNIX password:
passwd: password updated successfully
Enable SSH root login
By default SSH root login is disabled. Any attempt to ssh as root user will result in the following error message:
$ ssh root@10.1.1.9
root@10.1.1.9's password:
Permission denied, please try again.
root@10.1.1.9's password:
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The next command will configure SSH server to allow root ssh login:
$ sudo sed -i 's/#PermitRootLogin prohibit-password/PermitRootLogin yes/' /etc/ssh/sshd_config
Restart SSH server to apply changes:
$ sudo service ssh restart
SSH login as root
Your server now allows SSH login as root user. Use the password you set in the first step:
$ ssh root@10.1.1.9
root@10.1.1.9's password:
Welcome to Ubuntu Bionic Beaver (GNU/Linux 4.13.0-25-generic x86_64)
来源:https://linuxconfig.org/allow-ssh-root-login-on-ubuntu-18-04-bionic-beaver-linux