(1)apt-get remove openssh-server
(2)sudo apt install openssh-server
(3)sudo service ssh start
(4) ps -aux | grep ssh
(5)sudo apt install openssh-client
Solution for "Server unexpectedly closed network connection"
(1)apt-get remove openssh-server
(2)sudo apt install openssh-server
(3)sudo service ssh start
(4) ps -aux | grep ssh
(5)sudo apt install openssh-client