Abyss Web Server ships with a command line utility called autostart-setup which can configure your system to launch the server automatically at computer boot time and let it run in the background even if no user is logged on.
First, log in using a non-privileged user account (any account other than root), install Abyss Web Server and run it for the first time to have it create a default configuration file with the right settings.
Next, go to the directory where you have installed Abyss Web Server and execute: ./autostart-setup install.
autostart-setup may ask you to enter your root password if you are using a non-privileged user account. If this operation fails, log in as root and run autostart-setup install again.
Once Abyss Web Server is added to the list of programs which start automatically at boot time, you can manually stop it by executing the command: service abyssws stop or /etc/init.d/abyssws stop. To start it manually, use the command: service abyssws start or /etc/init.d/abyssws start.
If you ever want to remove Abyss Web Server from the list of programs which start automatically, go to the directory where you have installed it and execute: ./autostart-setup remove.