If you use Webmin to manage your server, you will eventually come across upgrades which will seem to ‘break’ your install. After upgrading, you’ll lose the ability to log in, and it seems as though the whole thing is just borked. In reality, you just need to restart the webmin daemon. Since this only happens when you reboot or start it manually, you’ll need to either reboot or start it manually.

At the command line, type (as root):

# /etc/webmin/start

After logging in you can verify the upgrade was successful and make sure that webmin starts upon system boot, just in case.