ssh:secure shell
Ubuntu does not install the sshd service by default, centos is installed by default, but you also need to enable the monitoring port 22 service.
sudo apt-get install openssh-server
sudo service sshd restart
After that, the service is turned on, and the 22nd service is monitored at the same time
Personal understanding of openssh-server is similar to a system software/service. After installation, it will start the sshd daemon and listen on port 22
The sshd process can be controlled through service ssh
I tried to connect many times, but I couldn't connect to the linux server remotely through ssh
Reason: ubuntu's ssh service may be shut down
After the server restarts the ssh service, you can log in