The previous instructions refered to a standard installation, with one unique Bugzilla database. However, you may want to host several distinct installations, without having several copies of the code. This is possible by using the PROJECT environment variable. When accessed, Bugzilla checks for the existence of this variable, and if present, uses its value to check for an alternative configuration file named localconfig.<PROJECT> in the same location as the default one (localconfig). It also checks for customized templates in a directory named <PROJECT> in the same location as the default one (template/<langcode>). By default this is template/en/default so PROJECT's templates would be located at template/en/PROJECT.
To set up an alternate installation, just export PROJECT=foo before running checksetup.pl for the first time. It will result in a file called localconfig.foo instead of localconfig. Edit this file as described above, with reference to a new database, and re-run checksetup.pl to populate it. That's all.
Now you have to configure the web server to pass this environment variable when accessed via an alternate URL, such as virtual host for instance. The following is an example of how you could do it in Apache, other Webservers may differ.
<VirtualHost 126.96.36.199:80> ServerName foo.bar.baz SetEnv PROJECT foo Alias /bugzilla /var/www/bugzilla </VirtualHost>
Don't forget to also export this variable before accessing Bugzilla by other means, such as cron tasks for instance.