Provision ACL
Check out the module page: http://drupal.org/project/provisionacl
First, you'll need a running Aegir install (1.0-rc3 or later), see http://community.aegirproject.org/installing. Most (if not all) of these commands will have to be run as root (or using sudo, etc.)
Download and install provision:
drush dl provisionacl
Enable ACLs on your filesystem (using root "/" here):
mount -o remount,acl /
Install ACLs:
apt-get install acl
Create a UNIX group (in this case the group is called "devs"):
groupadd devs
Add one or more UNIX users that you want to give access to that group. For an existing user (socrates32), this would look like:
usermod -a -G devs socrates32
For a new user (ergonlogic), this would look like:
useradd -G devs ergonlogic
Create a client (should be called "devs" for this example) in the frontend at /node/add/client.
Create a site for the client in the frontend at /node/add/site.