There are only two types of security modes for Samba, share-level and user-level, which are collectively known as security levels. Share-level security can only be implemented in one way, while user-level security can be implemented in one of four different ways. The different ways of implementing a security level are called security modes.
14.4.1. User-Level Security
User-level security is the default setting for Samba. Even if the
security = user directive is not listed in the
smb.conf file, it is used by Samba. If the server accepts the client's username/password, the client can then mount multiple shares without specifying a password for each instance. Samba can also accept session-based username/password requests. The client maintains multiple authentication contexts by using a unique UID for each logon.
security = user directive that sets user-level security is:
security = user