Multi site installations...need more details.

It helps to recognize that there are two parts to multisites:

1. Getting the webserver to load the same index.php for multiple sites (domainnames, directories)
2. Configuring drupal

1. Getting the webserver to load the same index.php for multiple sites

I will assume
- Apache
- Windows NT flavor (XP, 2000, etc)

This can be achieved by

1. Virtual hosts pointing to the drupal installation directory
2. Aliases pointing to the drupal installation directory
3. Symbolic links guiding the webserver to the drupal installation directory (in your case site2 would be a symbolic link to mainsite)

To develop sites locally it is usually best to use subdomains on localhost (site1.localhost, site2.localhost) as this can prevent a lot of link problems later when you have domain1.com, domain2.com etc. So I'll use that as an example.

Here's a sample / simple Virtualhost configuration for XAMPP (usually goes into httpd.conf (for xampp extra/httpd-vhosts.conf):

NameVirtualHost 127.0.0.1

<VirtualHost 127.0.0.1:80>
ServerName localhost
DocumentRoot "C:/xampp/htdocs"  # Default XAMPP htdocs
</VirtualHost>

<VirtualHost 127.0.0.1:80>
ServerName site1.localhost
DocumentRoot "c:/drupal_installs/drup_47"   # Drupal installation directory
    <Directory />
      Options All
      AllowOverride All        # Simply allow all directives to be overridden in .htaccess
      Order allow,deny
      Allow from localhost     # Only allow access from localhost
    </Directory>
</VirtualHost>

<VirtualHost 127.0.0.1:80>
ServerName site2.localhost
DocumentRoot "c:/drupal_installs/drup_47"    
    <Directory />            
      Options All
      AllowOverride All      
      Order allow,deny 
      Allow from localhost 
    </Directory>
</VirtualHost>

Always restart Apache after changing the configuration.

Of course, the OS needs some persuasion to resolve the domainnames site1.localhost and site2.localhost to 127.0.0.1.

Open %windir%\system32\drivers\etc\hosts and append

127.0.0.1 site1.localhost 
127.0.0.1 site2.localhost 

Most unices also carry a hosts file in etc.

Check that Apache loads drupal for site1.localhost & site2.localhost (error pages).

2. Configure Drupal

Create in the drupal installation directory the directories:

sites\site1.localhost
sites\site2.localhost

Copy the default settings.php into those directories and adapt the $db_url and $db_prefix variables.

For your situation, create one database and load the database layout twice, each time with the desired prefixes.

Your multisite installation should be working now.

ps: while tempting to multipost, better put all info in one place.
--
The Manual | Troubleshooting FAQ | Tips for posting | Make Backups! | Consider creating a Test site.

Reading through "all" comments regarding multi site setup leaves us somewhat confused, as it seems to be many different solutions for this issue.
What we would like to accomplish is this:
- one main site (portal for a number of organizations)
- a number of "subsites" (organization sites)

Each subsite will have it's own users, themes etc i.e. much of a standalone website, but some content may be shared from main portal to every subsite.
All sites will have ads and other "site specific things" so we think of using one database, with prefixed tables to get stats, design and users separated from each subsite.

Example:
www.mainsite.com
- membersite1
- membersite2

The URL:s for membersites are not that important as long as they can be reached directly i.e. ~membersite1.mainsite.com or ~mainsite.com/membersite1.

What would be best to accomplish this? Multi site setup, one database or many?
BTW: as of now we do not have full controll over the web server..

A pointer to any good documentation describing this scenario would be highly appreciated (running Drupal 5 now).

mi-sjo