This applies to NoMachine Enterprise Terminal Server and its Enterprise Terminal Server Nodes.

1) Create a node group:

$ sudo /etc/NX/nxserver --nodegroupadd NODEGROUP

2) Add a node to NODEGROUP:

sudo /etc/NX/nxserver --nodeedit NODE:PORT --node-group NODEGROUP

where NODE:PORT is the name of node as in output of 'nxserver --nodelist'

3) Create a NoMachine group of users

$ sudo /etc/NX/nxserver --groupadd USERGROUP

and add the user to that group:

$ sudo /etc/NX/nxserver --useradd USERNAME --group USERGROUP

or

use an existent system group of users.

4) By default, all nodes are allowed to all users. Deny group of nodes to group of users:

$ sudo /etc/NX/nxserver --ruleadd --class node --type NODEGROUP --value no --group USERGROUP