By default, NX is configured to allow access for any system user, as long as the user provides valid credentials for the SSH login.

As an option, NX offers an alternative authentication method relying on NX Password DB. The separation between the system password and the NX password allows the administrator to allow remote access to the system by no other means except NX.  The system administrator can then use the NX tools to implement effective accounting of the system resources used by the user.

To restrict access to the system  the system administrator has to configure the server to use the NX Password DB by editing the server configuration file, i.e. /usr/NX/etc/server.cfg and setting:

EnablePasswordDB = "1"