Alias /wordpress-mu /usr/share/wordpress-mu

<Directory /usr/share/wordpress-mu>
  AllowOverride Options
  RewriteEngine On

  RewriteBase /wordpress-mu/

  #uploaded files
  RewriteRule ^(.*/)?files/$ index.php [L]
  RewriteCond %{REQUEST_URI} !.*wp-content/plugins.*
  RewriteRule ^(.*/)?files/(.*) wp-content/blogs.php?file=$2 [L]

  # add a trailing slash to /wp-admin
  RewriteCond %{REQUEST_URI} ^.*/wp-admin$
  RewriteRule ^(.+)$ $1/ [R=301,L]

  RewriteCond %{REQUEST_FILENAME} -f [OR]
  RewriteCond %{REQUEST_FILENAME} -d
  RewriteRule . - [L]
  RewriteRule  ^([_0-9a-zA-Z-]+/)?(wp-.*) $2 [L]
  RewriteRule  ^([_0-9a-zA-Z-]+/)?(.*\.php)$ $2 [L]
  RewriteRule . index.php [L]
</Directory>