If you are looking for a Windows Active Directory replacement, Univention Corporate Server (UCS) is the best Linux distribution that can do best on it. UCS has a built in Active Directory (OpenLDAP) feature that can replace Windows Active Directory. It easy to install and manage. There is a new feature on UCS which allows us to synchronize account data between existing Active Directory server and UCS domain.
Univention Active Directory connection module allows us to sync account data and/or configure UCS server as a part of any existing Active Directory. You can install this module from the Software Center. To sync the account data from existing AD to UCS Domain, follow these steps:
Open Active Directory Connection module
Select the second radio button and press Next. Enter the Active Directory domain credential here.
UCS Active Directory Connection supports 3 different synchronization method. On this example I select the bidirectional sync mode.
In a moment the sync process is completed. Now you can check your account data.