Remote X

Everything we have looked at so far has been about command-line remoting, with no mention of how to bring up a graphical user interface. There are two ways of doing this in Linux: the X Display Manager Control Protocol (XDMCP) and Virtual Network Computing (VNC). The former is specific to the X Window System and is very tightly integrated with the rest of the graphical system but is also very insecure. VNC is more modern and very widespread but insecure in some implementations. Both are being used with Fedora, so we will cover both here.

XDMCP

Unless you have Fedora configured to log in a specific user automatically, you will be familiar with the user login screen that appears at bootup. What you are seeing is the GNOME Display Manager (GDM), which runs your X sessions, checks passwords, and so forth. What you are doing is logging in to the local machine because that is the default configuration.

However, GDM is also equipped to allow other network users to connect to your machine through the XDMCP protocol. There are various reasons for using XDMCP, of which the most popular is that many modern machines are large and noisy. They have big hard drives, CPUs with huge fans, powerful graphics cards, and so do not fit into a peaceful living room. On the flip side, a thin client (a machine with very little CPU power and no hard disk of its own) is silent but not powerful enough to run GNOME or OpenOffice.org.

The solution is to have your powerful machine locked away in a cupboard somewhere with a Wi-Fi connection attached and your quiet thin client sitting in the lounge also on the Wi-Fi link. The thin client connects to the powerful machine and runs all its programs from there, with all the graphics being relayed over the network.

With Fedora, this is easy to do. On the server side (the powerful machine), you need to check one box, and on the client side (the less-powerful machine), you need to check another box. We will start with the server side first. Select System Settings, Login Screen; then select the XDMCP tab and click Enable XDMCP. On the client side, select System Settings, Login Screen; then select the Security tab and click the Allow Running XDMCP Chooser from the Login Screen. You should also make sure the Show Actions Menu box is checked.

Now, from the client side, log out from your desktop so that you return to the Fedora login screen. When it prompts you for your username, press F10. A menu appears with an option labeled XDMCP Chooser. Select that and a new dialog box appears with a list of local XDMCP servers that are willing to accept your connectionyou should see your server in there. Select it and click Connect; you will see a login screen from that server, inviting you to log in. You will, of course, need a valid account on the server to be able to log in; however, that is the only thing you need.

As you can see, because XDMCP is so core to the X Window System, it is easy to set up. However, as you will find as you use it, XDMCP is very sloweven on a Gigabit Ethernet network, it will chew up a substantial percentage of bandwidth. It is also insecure. Anyone can monitor what you are doing with very little work. Because of these two flaws, XDMCP should never be used outside a trusted network.

VNC

The next step up from XDMCP is VNC, which was developed at AT&T's Cambridge Research Laboratory in England. VNC is widespread in the Linux world and, to a lesser extent, in the Windows world. Its main advantage is its widespread nature: Nearly all Linux distributions bundle VNC, and clients are available for a wide selection of platforms.

By default, Fedora installs the VNC server component but not the client component. Go to the Add or Remove Packages dialog box and select System Tools. Then select vnc to install the client, go to Network Servers, and select vnc-server to install the server.

With that done, all that remains is to tell Fedora who should be allowed to connect to your session. This is done from the Remote Desktop option on the Preferences menu. By default, your desktop is not shared, so check Allow Other Users to View Your Desktop to share it. You should also check Allow Other Users to Control Your Desktop; otherwise, people will be able to see what you are doing but not interact with the desktopwhich is not very helpful.

The second set of options on that screen is important. If you are using this as a remote way to connect to your own desktop, deselect Ask You for Confirmation. If this is not done, when you try to connect from your remote location, Fedora will pop up a message box on the local machine asking Should this person be allowed to connect? Because you are not there to click Yes, the connection will fail. If you want to let someone else remotely connect to your system, keep this box enabled so that you know when people are connecting. You should always enter a password, no matter who might connect. VNC, like XDMCP, should not be considered secure over the Internet, or even on untrusted networks.