Remote Desktops and Thin Clients
Steve Davison wrote: > Shirro, > the agenda for the next meeting sounds quite interesting, Trev. > and I will be there again. > > My day job is pretty quiet over the next week so have plenty of time to > do a bit of reading; do you have any links to some of the stuff you'll > be showing us on Tuesday night? >
Sure.
This is done quickly, so if there is anything innacurate, please let me know.
VNC
VNC was a simple protocol that originated at a research lab in the UK. They wanted to be able to have staff walk around a building wearing a radio id tag, and their screens would follow them. So you sit down at a computer, and you get your desktop - walk down the corridor and sit at another machine, and get the same desktop with your apps open exactly where you left them.
The protocol was ridiculously simple and is called RFB (remote frame buffer). It is so simple, lots of clients and servers have been written for everything from PDAs up. The original VNC server had a built in webserver, so if you didn't have a vnc client, you could connect with a web browser and it would display a java viewer.
Later it was refined to give better compression. The Windows server hooks were improved. And specialist applications arrived (like reflectors, so a teacher can mirror a display to all their students PCs)
VNC servers and clients are available for most platforms. You can administer a Windows server from your PDA, or get to your Windows admin tools from your Linux desktop.
SSH
SSH basically is just an encrypted replacement for telnet. It lets you connect to the command line of another computer. It also lets you setup other encrypted channels, and is used for vnc and X11 sessions since these are not secure by themselves.
Since a lot of us are forced to use Windows boxes, or clients use only Windows desktops, an ssh client for Windows is absolutely essential. There is only one worth knowing about and that is Putty. Put it on your USB key or a cd and carry it everywhere.
Remote X11
XWindows has always been able to display across a network. It is too slow to work well across a slow internet link, but it works fine across a LAN.
If you ssh into a remote linux box with the command
ssh -X remotemachine
it will forward your X connection over an encrypted channel. Any X windows program you run from ssh will appear on your local machine, but run on the remote machine. VNC is also often tunneled across ssh for security.
RDP
A company called Citrix made a shitload of money selling a way to run Windows client-server.
A lot of Windows applications are very badly written file based databases that do not scale across WANs because they require local shared access to files to work efficiently. Access databases are an example of this. Instead of rewrite software as modern multi-tier applications, places like dental surgeries, and insurance companies started running their Windows applications on a terminal server so their remote offices could share a database.
People also started to realise that looking after a lot of Windows desktops is a pain, and very expensive. So in some schools and businesses, Windows is run as a thin client to reduce costs.
Microsoft realised Citrix was onto something and so stepped in and stole their business. The protocol used by Windows Terminal Server is called RDP. All modern versions of Windows have a limited terminal server capability built in - check out remote assistance on 2000/XP.
RDP clients exist for Linux that let you connect to a Windows computer for support, or to a Windows Terminal Server to run Windows applications.
Citrix make a linux client, but the main one to know about is rdesktop
No Machine NX
An Italian company called No Machine developed a really efficient way of moving XWindows data across a network. They use compression and caching to get amazing results. Unfortunately they seemed to be largely ignored, althogh their product is brilliant. It gives you fast remote access to a Linux box, with sound, local printers, and access to your local files.
Much of the NX core system was available as open source code, and is now getting more attention. A FreeNX server has been developed and is available in Knoppix. It still doesn't have all the features of the No Machine system, but it is still very usable.
As far as I am concerned NoMachine is the ultimate for remote access to a Linux GUI.
LTSP and K12LTSP
XWindows has always been network transparent. The Linux Terminal Server Project just packages everything you need to run thin clients with Linux. The K12LTSP version is aimed at schools. Samps knows a hell of a lot more than me about this, and I hope we can get him to a meeting.
The obvious advantage to a school, is that you can reuse your old computers as terminals and all you have to buy is one big server. This is much lower maintenance, and a cheap solution.
PXES
LTSP aims to be a complete distribution for running terminal services under Linux. PXES just aims to be a client. It can boot directly of the network into a selection of remote viewing tools including all of the above. If you have Windows terminal servers, Linux terminal servers, machines you have to administer with ssh, machines running VNC servers, you can connect to them all with PXES.
PXES has a configuration utility so you can easily customise the distribution for your needs.
All this and it fits in under 5M, so you can imagine how fast it boots.
The Meeting
There will be no exams on this ;-)
We will probably start with running a remote X application over ssh from the Linux desktop
We will probably boot a few of the computers in PXES over the network and connect using a few protocols.
Hopefully we may see an LTSP demo. How about it Samps?
If the school network is not too slow, and the ports are not blocked, we might play gnometris and read slashdot using a remote SuSe Gnome desktop sitting on a No Machine demo server in Italy.
We will almost certainly look at using VNC on Windows/Linux to remote admin/monitor Linux/Windows.
Someone will probably bring in a PDA with Linux on it. (Any offers?)