On the commandserver navigate to directory sw-depot and futher down to linux\client.
Copy the installer (.run) onto the /tmp directory of the Linux system.
Start the installer as root or using sudo.
Example:
root@caesium:/tmp# ./Client-DataCenter-6.5.0_b3236-linux-x64-installer.run
Answer the questions and be careful to supply the correct commandserver IP or name.
The client will install and try to register (that is: add the name to commandserver DB NODE table). If the client does not show up in GUI->NodesManagement, use [context menu]AddNode to add the node.