ssh: connect to host localhost port 22: Connection refused

I have installed hadoop and ssh. hadoop was working fine, then today I am getting the error below when I run the command sbin/start-dfs.sh: Starting namenodes on [localhost] localhost: ssh: connect to host localhost port 22: Connection refused Starting datanodes localhost: ssh: connect to host localhost port 22: Connection refused Starting secondary namenodes [chbpc-VirtualBox] chbpc-VirtualBox: ssh: connect to host chbpc-virtualbox port 22: Connection refused I've checked the ssh status, and I have the following error: ssh.service - OpenBSD Secure Shell server Loaded: loaded (/lib/systemd/system/ssh.service; enabled; vendor preset: enabled) Active: failed (Result: start-limit-hit) since Tue 2020-02-04 15:34:10 +04; 3h 35min ago Process: 946 ExecStartPre=/usr/sbin/sshd -t (code=exited, status=255) Feb 04 15:34:09 chbpc-VirtualBox systemd: ssh.service: Control process exited, code=exited status=255 Feb 04 15:34:09 chbpc-VirtualBox systemd: Failed to start OpenBSD Secure Shell server. Feb 04 15:34:09 chbpc-VirtualBox systemd: ssh.service: Unit entered failed state. Feb 04 15:34:09 chbpc-VirtualBox systemd: ssh.service: Failed with result 'exit-code'. Feb 04 15:34:10 chbpc-VirtualBox systemd: ssh.service: Service hold-off time over, scheduling restart. Feb 04 15:34:10 chbpc-VirtualBox systemd: Stopped OpenBSD Secure Shell server. Feb 04 15:34:10 chbpc-VirtualBox systemd: ssh.service: Start request repeated too quickly. Feb 04 15:34:10 chbpc-VirtualBox systemd: Failed to start OpenBSD Secure Shell server. Feb 04 15:34:10 chbpc-VirtualBox systemd: ssh.service: Unit entered failed state. Feb 04 15:34:10 chbpc-VirtualBox systemd: ssh.service: Failed with result 'start-limit-hit'. How can I fix this?