Managing your own web server not only means ensuring that your client's websites are being displayed. It also means that you need to make sure that your client's email is uninterrupted.
The tail Linux command is a very useful command for viewing logs. It is designed to show the end of a file on a screen. It can however be set to automatically set to always display the end of a file. Want to monitor your Debian web server's SSH logins? run this simple command:
tail -f /var/log/auth.log
In particular, I've found it very useful while attempting to troubleshoot problems with an exim4 mail server on a VestaCP installation by watching inbound and outbound email traffic.
Console programs can be ugly. Fortunately, there is some built in characters that can produce table borders that can help liven things up a bit. (just a little)