Install openssh-server
sudo apt install openssh-server
sudo /etc/init.d/ssh start
Test the config file
If the server fail to start, to see what’s wrong
sudo /usr/sbin/sshd -T
A backup file for sshd_config
sudo cp /usr/share/openssh/sshd_config /etc/ssh
Start and stop sshd
sudo systemctl start ssh.service
sudo /etc/init.d/ssh start
sudo systemctl stop ssh.service
Generate Host Keys
sudo ssh-keygen -A
Privilege separation user sshd does not exist
add sshd:x:74:74:Privilege-separated SSH:/var/empty/sshd:/sbin/nologin to /etc/passwd and restart the service.