Samba 4 review: No substitute for Active Directory -- yet
Samba's open source alternative to Microsoft's domain controller is a good start, but not ready for prime time
Samba 4.0 is a milestone release that brings Active Directory functionality to the open source SMB/CIFS (Server Message Block/Common Internet File System) file and print server. Samba 4.0 can serve as an Active Directory Domain Controller, provide DNS services, handle Kerberos-based authentication, and administer group policy. The Samba 4.0 Domain Controller can even be managed using the native Windows Active Directory admin tools.
However, there are restrictions in this release -- mainly issues with file replication -- that limit the number of Domain Controllers you can join to only a single domain. Support for cross-forest trusts and multiple domain controllers is still to come. When that support arrives, Samba will be truly useful as an Active Directory replacement. Until then, the Domain Controller functionality is suitable mainly for testing. Not many environments can make good use of a single domain controller.
Beyond file and print services
SMB is the protocol behind all network file communication used natively by Windows Server and Windows clients; it's also known as CIFS. Support for SMB/CIFS on other operating systems has primarily come from the Samba project. Samba started back in 1992 as a way to connect Unix and Linux machines to Microsoft's LAN Manager network operating system. It's provided the plumbing necessary for Unix and Linux machines to connect to Microsoft networks ever since.
The most common use of Samba is still in the client role, but that has changed along the way with the ability to provide file and print services to Unix and Linux clients, as well as systems running various versions of Windows.
Samba has maintained a solid capability as a file server and client but has never had the ability to function as an Active Directory Domain Controller until now. Samba 4.0 has been under development for quite a long time, and the Domain Controller functionality has been available in beta form during the later stages prior to release. Samba 4.0 delivers a stable release of this new capability but in a severely limited form.
For Samba 4.0 to be useful in large and multisite environments -- the sort that rely on Active Directory -- it will need to support cross-forest trusts and multiple domain controllers. Support for multiple domain controllers requires directory and file system replication to maintain the user database and the sysvol and netlogon shares. (The sysvol share stores the Group Policy Template along with other system templates and scripts, and the netlogon share contains system-wide logon scripts for the likes of assigning home directories and updating virus definitions.) Directory replication works reliably in this release, but the file system replication piece remains under development.