Knowledge point 1: ubuntu is the Linux system distribution of the debian system.
Knowledge point 2: If you want to remote to Linux through tools such as xshell, you need openssh support.
Knowledge point 3: The default Linux package manager of the debian system is apt
1. Openssh clean uninstall
sudo apt-get remove openssh-server openssh-client --purge -y
Uninstall the software and clear the openssh configuration file (under the /etc/ssh directory)
Two, openssh installation
apt-get install openssh-server openssh-client
3. openssh restart
systemctl restart ssh