How do I make an alias for a directory:
e.g. I have a directory "/library" in my main domain. In a subdomain I want to use an alias "/library" pointing to that main domain directory.

In Apache httpd.conf I can include the line:
Alias /library /home/httpd/vhosts/<domain>/httpdocs/library
but I don't know how to this on a server with Plesk.

 

Try to include it intro .htaccess. It it's not working, then use vhost.conf file in ~/conf directory.

 

.htaccess gave me an internal server error. The vhost.conf-solution works perfect. But you have to run a shell command after you placed vhost.conf-file. I found the documentation: http://download1.sw-soft.com/Plesk/Plesk7.1/Doc/html/plesk-7-reloaded-admin/apas02.html