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Are you adept with Virtual Network Computing (VNC)? If not, you'll find that learning even a little about this desktop sharing system pays off big in your daily development or system administration responsibilities.
If you're already familiar with VNC, even better: You're in a position to appreciate the latest innovations based on VNC. Wherever you start, the tour that follows:
- Introduction
- VNC as a configuration component
- VNC as a development platform
should include at least a few scenes that reinforce VNC's indispensability.
Easy introduction to a crucial tool
Indispensable is one of the best words to associate with VNC, incidentally; it
belongs in a category with ssh,
screen, Expect, and a few
other widely applicable tools that multiply productivity, not just boost
it. VNC's contribution is to make it easy for a computing process to run
here, but display there. You can use VNC to:
- Look over the shoulder of a colleague working 5000 kilometers away;
- Connect from home on the weekend to the display of a process that took all week to set up on your desktop at work;
- Guide an AIX newcomer in a different city through a point-and-click sequence hard to explain on the telephone;
and much more. Perhaps best of all, it should take only a few minutes to start.
For your first experiment, you need to:
- Install a VNC server, presumably on an AIX host;
- Install a VNC client or viewer, on any convenient networked desktop;
- Launch the server and viewer; and
- Start a test application that runs on one machine, and displays on the other.
Let's look at each step more carefully, to ensure your success.
VNC is based on a public networking protocol called RFB (see the
Resources below for further reading on the technical
topics this article raises). VNC software is available both in proprietary and
cost-free versions for a remarkable variety of platforms; VNC is useful on
everything from mainframes to wristwatch-sized gadgets. For AIX in particular, an
easy way to start is with the copy on the Toolbox for Linux® CD which comes with
AIX. A current RPM is also available through the IBM AIX Toolbox. Although you can
launch VNC as an unprivileged user, and it's possible even to install
local copies of it, you'll probably find it easiest for your first installation
simply to become root.
Let's be clear on what the first experiment will give. The "Toolbox" installation provides both a VNC server and client; the latter is often called a viewer. To start, you'll probably need only the server on your AIX host. On a viewing machine -- maybe not AIX, and maybe not even X11-equipped -- you need to select a viewer. For popular desktops like Windows®, Linux, and MacOS, there are many distinct viewers.
VNC contrasts with X11 in several ways. X11 has always been a recognized and well standardized way to view results of a remote computation, so in some ways X11 and VNC compete. Confusingly, the two also use terminology in superficially opposite ways:
- X11:
- Server displays graphics
- Client computes results to be displayed
- VNC:
- Server renders graphics -- typically on same host where computations are made
- Client or viewer displays graphics
From a networking perspective, these uses of "client" and "server" are consistent. The labels can puzzle the unwary, though.
X11 and VNC are at least as much teammates as they are rivals. You'll see below that VNC service under AIX typically relies on X11. The X11-plus-VNC combination has many advantages over X11 alone: For instance, VNC operates better, sometimes much better, than (pure) X11 when working over long or slow connections or both. Also, VNC viewers have no responsibilities for font management, and can be much easier to install than X11 servers. Nowadays, you rarely use X11 without VNC except on the console of a UNIX® host.
With your chosen parts in place, launch vncserver on the AIX host with
vncserver :2 or similar, and a password you keep safe.
This creates a new X server; give it something to show by also launching on your
AIX host xterm -display :2.
Now turn to a desktop where you've installed a VNC viewer. Launch a new viewer
pointed at $AIX_IP_ADDRESS:2, enter the password, and
you should soon see your AIX console, with a fresh
xterm already popped into place.
You've just achieved an important milestone. Your VNC session will "feel" something like X, in that you're viewing on a different machine than the one doing the serious computation. Notice, though, this difference from X: shut down the viewer. Restart it, and reconnect. You have the desktop back again, with all the programs still running! This demonstrates that, unlike conventional X11, VNC is "resumable."
There are many, many more experiments you'll want to do to customize VNC
to your situation. Keep in mind that, as already mentioned, VNC is an open
standard which supports an abundance of implementations. The Bull Freeware site,
for example, has an alternative server that, among other features, can be
effectively run by inetd.
Here are a few more possibilities to consider:
- With the
-geometryargument, you can set up a larger framebuffer. Most servers default to 640x480, a size that made more sense almost a decade ago when VNC was first invented than it does on common hardware now. - If your AIX installation is sufficiently up-to-date, you don't even need to
install a viewer to use VNC; just point a Java™-enabled browser to
http://$AIX_IP_ADDRESS:5802. Do you realize what that means? You can show collaborators your latest application with no installation at all. If they have a Java-enabled Web browser --and who doesn't, in 2007? -- you can give them a URL to your latest AIX-based creation. - Unlike X11, VNC allows several different remote viewers to connect
simultaneously. Read up on the
*sharedflags in the documentation for the VNC software you use. - Security is an issue. If you expose your VNC service on the Net at large, intruders will probe it. Leave it up long enough, and someone will "brute-force" through your password. The Resources at the end of this article point to the many possibilities for hardening VNC security.
- Be aware that most VNC components have conventions for offseting display and port number by 5800. Reference to X11 server display :2 is typically provided through port 5802, for example. While this, like so many UNIX practices, is configurable, it eases learning to recognize the starting point: :1-5801, :2-5802, and so on.
Think for yourself how many useful scenarios VNC makes possible. One example: You set up a demonstration on a dedicated machine in a laboratory, connected to special hardware, perhaps with hardware-locked licenses. You start a VNC server, and walk into a lecture hall or meeting room, where you show off your full display on a large-screen projector in a professional setting without having your audience trip over the cables and breadboxes in the back room.
VNC as a configuration component
VNC "plays nicely" with other components. It's not just that VNC supports several different options to make its use more convenient; it's configurable in ways that combine well with other practices you might already have. I work with university labs, for example, where dozens of machines are all simply configured to come up automatically with VNC servers running in standard ways. Among other benefits, that means that anyone in the labs can call for help at any time, and a support specialist can "look over his shoulder", even if the specialist is across the country at the time. This makes for much better manageability and economy than having to keep the labs populated at all times with a full complement of support specialists -- or, worse, leaving the students to fend for themselves.
The best way to think about VNC is to recognize that it's just one component in a movement toward virtualization. Computation, display, networking, management -- by standardizing them, they become "mobile," available anywhere a network reaches, and can be arranged to best serve your engineering or business criteria. Just because a motherboard or a display tube is physically restricted to a particular place is no reason your work should be.
Automation works equally well on the viewer side, of course; I have startup routines on my desktops that automatically connect to sessions on servers that I monitor all around the world. I tend to use few options on the viewer side -- sometimes color depth to reduce bandwidth requirements, or input or sharing configuration. For "chronic" use, I particularly like to turn off pointer and keyboard events, so my viewer is read-only. This prevents me from accidentally overwriting or otherwise affecting a remote machine, although I can still monitor exactly what it's doing.
Another facility AIX specialists should know is x11vnc. x11vnc is a VNC server tightly bound to physical hardware. x11vnc's emphasis on performance means that it's practical to view 3D OpenGL graphics through a VNC connection, and its portability allows it to serve from webcams, TV tuners, and other unusual hardware. x11vnc is compatible with most or all of the GXT*P video adapters in current AIX hardware.
Not all potential VNC-based accessories have already been written. It could well happen that you need a facility that doesn't yet exist -- a viewer on unusual hardware, say, or a record-and-playback facility that makes it easy to archive screen snapshots, or specialized video effects to support a teleconference, or a simple notification widget that requires console approval before allowing a VNC connection.
The wealth of open source VNC implementations means that you can study what others have done to program both the server and client sides of RFB. Moreover, there are a few high-level toolkits, like tclRFB (see Resources), that ease VNC programming.
The 0.5 release of tclRFB includes a 500 line example viewer. With the addition
of just a few extra lines, you can have the viewer automatically save an image of
its remote connection every ten seconds (see Listing 1 ).
Listing 1. Add a recording facility to the example tclRFB viewer
proc save_snapshot_and_repeat {canvas_name destination_file delay} {
set suffix [clock seconds]
$canvas_name postscript -file $destination_file$suffix.ps
after $delay [list \
save_snapshot $canvas_name $destination_file $delay]
}
set display_canvas .vp.fb
set file my_snapshot
set interval 10000 ; # Ten seconds.
save_snapshot_and_repeat $display_canvas $file $interval
|
While this example formats the snapshots as PostScript, other freely available libraries make it possible to generate MPEG, animated GIFs, and so on.
Most of what I've written here would have been true five years ago: VNC is also like Expect and screen and other productivity marvels in that almost all its functionality was present near its beginning, and much of what's happened since then has been no more than refinement. News in the VNC world mostly has to do with minor enhancements or corrections.
There are a couple of recent significant developments you should know, though:
- Synergy is software that lets multiple computers share a single mouse and keyboard. This is a different technology than VNC, but will interest some of the same administrators and developers who otherwise would use VNC.
- NX is open source terminal server software developed by a for-profit company. Its effect is to accelerate transmission of remote X11 or VNC or a few other supported technologies. If you aren't getting the performance you need for remote viewing, give NX a try.
The main point in all these explorations is to get to know VNC. You'll eventually find the refinements that work best for you. In the beginning of your VNC experience, concentrate on this: don't let physical distance come between you and a computer display you want to see, or have others see, or perhaps both, at the same time. Once you start using VNC, you won't want to live without it. As this article demonstrates, moreover, it takes little to start.
Learn
-
"Productivity
tips"
(developerWorks, September 2006): This article focuses on technologies, such as
VNC, that make a difference in the work you do each day.
-
"Expect
exceeds expectations"
(developerWorks, April 2002): Learn how to automate many tasks commonly thought to
be only interactive.
- Read the following documents on Secure Shell
(SSH):
- GNU Screen: The GNU Screen
roughly does for command-line connections what VNC does for visual displays. With
screen, you can use a single, even slow, command-line connection to manage several
character-oriented windows. You can flip between them, disconnect and reconnect
later from another location, and more. Like VNC,
ssh, and Expect,screenis a program you'll find indispensable. - RFB: RFB is a simple
protocol for remote access to graphical user interface. As an openly published
protocol, RFB has many implementations, both proprietary and free.
- IBM AIX
Toolbox:
This page includes VNC and scores of other useful software applications.
- Bull Freeware: This site includes an
alternative VNC server.
- This
Usenet thread:
Different AIX series have different graphical hardware. This discussion
illustrates how easy it is to bind VNC service to your host's main console, if
that's what you want.
-
"Create a VNC
system with tclRFB"
(developerWorks, August 2003): This article introduces tclRFB as a toolkit for VNC
programming.
- x11vnc: x11vnc is a VNC server
which builds in all sorts of features, including UNIX account and password
support, server-side scaling, file-transfer functionality, and OpenGL
compatibility.
- Synergy: Synergy lets multiple
computers conveniently share a single mouse and keyboard.
- NX: NX is a terminal server that
achieves remarkable performance in transporting, for example, VNC.
-
"Remote
computing with a Linux application server farm"
(developerWorks, February 2007): This article reports for developerWorks on VNC's
role in saving a university lab tens of thousands of dollars.
- "SSL
secures VNC applications"
(developerWorks, January 2007): Read this article and find out why it's very
common to "tunnel" VNC through SSH to secure a connection.
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Cameron Laird is a long-time developerWorks contributor and former columnist. He often writes about the open source projects that accelerate development of his employer's applications, focused on reliability and security. He first used AIX twenty years ago, when it was still an experimental product. He's been an enthusiastic consumer of and contributor to a variety of memory debugging tools through that time. You can contact him at claird@phaseit.net.
