This post will explain how to host multiple drupal sites using only one url on linux.
We have two sites a Dutch site and a French site and we want to host it under one url.
Setup your folders in de sites folders. Create a directory for the french site and create a directory for the dutch site. Both will have their own settings file.
In the root of your drupal installation create two symlinks. The two symlinks will point back to the root of your site.