"Joining" a Windows Active Directory domain means creating an account for the client PC in the Active Directory domain, and configuring the client PC to allow authentication requests to be handled by a Domain Controller.
Linux can be configured to support Active Directory, but it's a slightly more complicated procedure than the one used to join a Windows client to a domain. There's no single configuration file one can edit, and the procedure differs from one distribution to another.
If what you need is the ability to log on to the Linux system using Active Directory credentials, there are in fact several ways to accomplish that:
- Samba, which runs on most if not every Linux distribution, can easily join a Windows domain and provides a PAM module (pam_winbind) for authentication (see PAM below)
- the System Security Services Daemon (SSSD), a Fedora/Red Hat project, allows authentication against AD (using Kerberos), and can also cache credentials and identities locally (which could be useful for laptops on the move)
- various PAM modules allow authentication against the Kerberos component in Active Directory (pam_krb5) or the LDAP service (pam_ldap)
Which is best? It depends on what you're trying to accomplish, and to a smaller extent which Linux distribution you're running.