Which command can be used to define Samba share permissions effectively?

The command that effectively defines Samba share permissions is setfacl. This command is used to set access control lists (ACLs) on files and directories, allowing for more granular permission settings than the traditional Unix permission model provides. With setfacl, administrators can specify different permissions for different users or groups on a Samba share, enabling a flexible approach to access control based on specific needs.

When managing Samba shares, using ACLs can be particularly advantageous in mixed environments where users might belong to various groups or need specific access levels. This command allows for the fine-tuning of permissions beyond the basic owner/group/other classification, ensuring that the right users have the appropriate rights to access shared resources.

Other commands like chmod are used to change basic file permissions and do not offer the same level of detail when it comes to Samba shares. Similarly, smbpasswd is primarily for managing Samba user passwords, and smbcontrol is used for sending commands to a running Samba service, neither of which can define share permissions directly. Thus, setfacl is the optimal choice for managing share permissions effectively in a Samba environment.