A webserver isn't necessarily bound to a particular O/S. Hence, the term " linux webserver installation" isn't really all that meaningful. You need to state which web server you're using.
I am not familiar with Apache Server, but I am familiar with Tomcat. If it's a Tomcat server you can find out what the root directory is by opening a terminal and typing:
The first is the root for the server itself. The second is the root directory for your personal web apps (assuming you share the server). CATALINA_BASE may not be defined if you've got a basic setup.