Which directive in the smb.conf specifies the name of the Active Directory Domain?

The realm directive in the smb.conf file is used to specify the name of the Active Directory (AD) Domain to which a Samba server can connect. This is particularly relevant in environments where Samba is functioning as a domain member in an AD domain, facilitating better integration with Windows systems. The realm is typically configured in a format that adheres to the conventions used in Kerberos, which underpins the security and authentication mechanisms of Active Directory.

By defining the correct realm, you ensure that Samba can properly authenticate users and services against the AD domain, enabling features such as single sign-on and group policies. This is essential for seamless interoperability between Linux and Windows systems within a mixed environment.

Other options do not fulfill the role of specifying the AD domain name directly. For instance, ad_domain is closely related but used in different contexts and can be part of configurations for Samba when setting up AD support. The domain_name option generally refers to DNS-related settings, while netbios name is specifically for identifying the Samba server on the network rather than associating it with an Active Directory domain.