This method should only be used on a secure network behind a firewall as stated in the documentation:
XDMCP service should run only on trusted networks and you have to disable firewall for interfaces, where you want to provide this service.Any computer in the local network will be able to access the computers display so it is important you trust every computer.
To start with you need to edit the computer you want access to. As root edit the file /etc/sysconfig/displaymanager. Change the line:
DISPLAYMANAGER_REMOTE_ACCESS="no”To:
DISPLAYMANAGER_REMOTE_ACCESS="yes”Save the file and exit. You now need to restart XDMCP by typing:
rcxdm restartNow any computer on the network can gain access to the display of this computer. To gain access use the command on the remote computer:
X :1 -query <IP address of first computer>If everything has worked the login screen of the remote computer will load. You can switch back to your own computer’s display by pressing ctrl+F7 and then go back to the external computer again by pressing ctrl+F8.
If ctrl+F8 doesn’t work then try some other F keys, it’ll be in one of them.