<VirtualHost *:80>
        ServerAdmin webmaster@localhost

        ServerName example.com
        ServerAlias *.example.com
        VirtualDocumentRoot /home/%1/www/html
        <Directory />
                Options FollowSymLinks
                AllowOverride All
        </Directory>

        ScriptAlias /cgi-bin/ /usr/lib/cgi-bin/
        <Directory "/usr/lib/cgi-bin">
                AllowOverride None
                Options +ExecCGI -MultiViews +SymLinksIfOwnerMatch
                Order allow,deny
                Allow from all
        </Directory>

        ErrorLog /var/log/apache2/error.log

        # Possible values include: debug, info, notice, warn, error, crit,
        # alert, emerg.
        LogLevel warn

        CustomLog /var/log/apache2/access.log combined

    Alias /doc/ "/usr/share/doc/"
    <Directory "/usr/share/doc/">
        Options Indexes MultiViews FollowSymLinks
        AllowOverride None
        Order deny,allow
        Deny from all
        Allow from 127.0.0.0/255.0.0.0 ::1/128
    </Directory>

</VirtualHost>

First of all this refers to a clean Ubuntu 10.04 install with the LAMP and OpenSSH packages installed, but can probably be applied in most cases.

Duplicate the file /etc/apaches/sites-available/default, and name it subdomains.

Edit the new file to look like this one.

Enable the vhost_alias module, "a2enmod vhost_alias".

Activate the new virtual host, "a2ensite subdomains".

Reload apache, "/etc/init.d/apache2 reload".

In order to change the configuration to your needs, [you can go here](
http://httpd.apache.org/docs/2.2/mod/mod_vhost_alias.html)

Ubuntu apache vhost_alias setup

apache, ubuntu

Apache