Virtual Network Computing
from ORL

Frequently Asked VNC Questions

VNC hasn't been out very long, so we're still building this list.  The mailing list archives are also available, and they will also be a good source of help.

Q. I've tried running the Linux Xvnc server, and it can't find the fonts despite the fact that I've set the font path correctly.

The Xvnc server doesn't currently understand compressed fonts as used by Xfree86. You can either use a font server (suggested by Alan Cox alan@cymru.net ), or  you can decompress the fonts (gunzip *.pcf.gz in the fonts dirs) and then in each font dir run mkfontdir to rebuild the fonts.dir file.

Q. The Windows server crashes on Windows 95.

Yes, annoying, isn't it?  It usually runs for a little while and then dies.   We haven't found any obvious memory or resource leaks. But this is why we only advertise it as an NT 4 server!  Try the Win32test R6 release on the download page and let us know if this improves it.

Q. Will VNC work through a firewall?

It depends on your firewall, and whether you want to access a server inside your firewall from elsewhere, or a server outside your firewall from inside.  

Generally firewalls are designed to prevent incoming connections except to certain well-known machines and ports.  If you can configure these to include your VNC server, then you will be able to access it from anywhere in the world.  There is a good argument to be made for the fact that VNC is less of a security risk than X, so if your site doesn't allow X in or out it may still allow VNC.

Many modern firewalls will allow outgoing connections initiated from inside, so you can often access servers on outside machines.  You may need to adjust or recompile the viewer source if, for example, you want to include SOCKS support.

It's a pity that Java within a browser doesn't automatically use SOCKS if the browser is configured to use it.  There's probably Java SOCKS suuport out there somewhere...

Q. How secure is VNC?

Access to your VNC desktop generally allows access to your whole environment, so security is obviously important. VNC uses a challenge-response password scheme to make the initial connection, but after that the data is unencrypted and could, in theory, be watched by other malicious users, though it's a bit harder to snoop a VNC session than, say, a telnet, rlogin, or X session.  Since VNC runs over a simple single TCP/IP socket, it should be easy to add support for SSL or some other encryption scheme if this is important to you.  Please let us know if you do this!

Q. How do I make VNC go faster?

We find VNC to be perfectly acceptable as our normal method of accessing Unix desktops on a daily basis.   This is over a 10 M/bit ethernet on reasonably modern machines, using the X or Win32 viewer.  Because Windows gives us fewer hints about what it's doing, and because we don't have the source code for Windows, the NT server has to work harder to find out what's changed, and so a really fast machine should make a big speed difference.  For more information about how the Windows server works, see the WinVNC documentation.

There are several things that can slow any VNC session down, however, and you may like to consider these if you find it too slow:

• Unusually 'busy' desktops.  The VNC protocol is very efficient at rendering areas of a single colour, such as you generally find on window title bars, scrollbars, backgrounds of pages etc. But if, for example, you have pretty 24-bit photographs of your girlfriend as your screen background, or dithered title-bars on your windows, you may pay a price for the aesthetics.
• Hi-colour desktops.   Don't use 24-bit colour if you can use 16 or 8 equally well. Remember, on Unix you can run multiple servers, so I have a big 16-bit desktop for normal work and a small 8-bit one for when I log in from home.  The server can send out a wide range of pixel formats, and some viewers will allow you to request a specific format for that session. On the Windows viewer, for example, if you click Options... when making the connection, you can request only 8-bit pixels from the server - useful if the network gets slow.
• Elderly graphics cards or drivers may make quite a difference; this is a graphics-intensive application!
• Some applications are not very economical about redrawing their display.  Early versions of Unix Netscape, for example, tended to draw everything twice when scrolling, which did nothing to help the smoothness under VNC.
• Some Java Virtual Machines are particularly fast at reading from the network and particularly slow at drawing to the screen, or vice versa.  With the Java viewer it is worth experimenting with the encodings available from the Options menu, as we sometimes find big differences in speed.

Q. Are you planning support for Macintoshes, AIX, HP-UX, SGI, Win 3.1, Windows CE, my favourite platform ?

We have provided VNC on all the platforms we use here, and it's difficult to provide binaries for anything we don't have, and it takes a while to get up to speed on new platforms, so we're unlikely to do any others in the near future.  Remember that a viewer is available for any platform which runs Java, though the speed may vary quite a bit. But for many platforms it should not be difficult to compile at least the viewer.

If anyone tailors the sources for a particular platform we will happily either incorporate the changes in the main source distributions or make the patches available from our site.

Q. Any other tips?

Several people have indicated that they have to use Windows occasionally but prefer to use Unix most of the time, and so want to access a PC under the desk from the Unix box.

Here's a suggestion: all other things being equal, I recommend using the Windows box to view the Unix machine rather than the other way around.  This is chiefly because Windows generally works better as a client than as a server, and also because PC graphics cards are often better than those in Unix workstations.  Remember, you can create a VNC session of any pixel depth you like.  For my day-to-day work I use a Solaris 16-bit VNC session displayed on my PC.  Few of our Sun machines have more than 8-bit color hardware, but the PC has plenty of bits to spare.

If you're very anti-Windows you can make your VNC desktop the same size as the screen and set the taskbar to 'Auto hide' and just pretend you're on an X terminal, but pop up the Start menu when you have to use PowerPoint....