The lab computers are intended to be usable remotely. This page is an attempt to describe how to do that. If your network connection is reasonably quick, you can work with the same interface that you'd have in the lab, but getting that set up involves several steps.
In what follows, we'll refer to the computer you are sitting at as
your computer, and whatever lab computer you are using as
cslabNN, where the NN will actually be anything in the
range 01 to 25. We'll also use the fictional username
mortimersnerd. (Note that some usernames have one or
more dots in them.)
You need two pieces of software on your computer: a secure shell (SSH) client and a VNC viewer.
The first program that you need is a SSH client and terminal emulator. If
your computer runs Mac OS X, you already have what you need. If you run
Linux, make sure that you have OpenSSH installed.
If you have MS Windows, you'll need to add something; we suggest the program PuTTY, which you can download (at no cost) from
http://www.chiark.greenend.org.uk/~sgtatham/putty/
(If that doesn't work, try the mirror site here, or here.) You probably want the latest release version, and the specific file you want is probably the Windows installer. Install the program.
VNC is a system that provides remote access to "virtual desktops" on a variety of computers. We provide the half of the system (called the VNC server) that creates the desktop on a lab machine. You need to supply the other half (the VNC viewer) for your own computer. Free versions are available for most popular computer systems. On Mac OS, your best bit is (despite a corny name) is Chicken of the VNC. (There is a newer version of this program, known simply as Chicken; it has a nice feature to make remote connections simpler, but it crashes too much.) On MS Windows, we have experience with the viewer from Real VNC (look for the Free Edition) and TightVNC. On Linux, install a package that provides a "VNC viewer".
If you are on campus, you should be able to connect directly to a lab computer; if you are not on campus, you'll need to see the slightly longer instructions below The first thing you need to be able to do is to do a basic connection to a lab computer with your SSH program. So start by picking a number in the range 01-25. (Keep the leading zero on it if it is less than ten.) We'll use 04 as an example. You also need to know your lab username; our example will be mortimersnerd.
(MS Windows users may wish to jump ahead.)
To connect to cslab04.wheaton.edu, open a
Terminal window, and type the command
ssh mortimersnerd@cslab04.wheaton.edu
The first time you connect to a particular machine, you may get a message
like
That warning is a bit of paranoia; you're probably OK, but the SSH software normally checks to make sure that you are connecting to the machine you intend; so it keeps a local list of "known hosts".Warning: Permanently added the RSA host key for IP address '10.22.84.132' to the list of known hosts.
If, for some reason, the machine you are trying to connect to is not working, you might see
If that happens, try another number. If nothing works, you'll need to troubleshoot your network connection--or we have a big problem in the lab.ssh: connect to host cslab04.wheaton.edu port 22: Operation timed out
You'll be prompted for your (lab) password; if you give it correctly, you should see a shell prompt--just as you would if you were to open a Terminal window when sitting at one of the lab computers. Congratulations. You've made the first step. Skip over the instructions for MS Windows.
Connecting with PuTTY looks a little different. When you launch PuTTY,
you'll see a dialog box. First, set the 'Connection type' to
SSH. Then fill in the 'Host Name' box with
cslab04.wheaton.edu. Then click on 'Open'.
If you get Network error: Connection timed out, try another
machine. (You can right-click on the title bar to get a menu and select
'New Session...' to get a new dialog.) If you can't connect to any of the
machines, either you have network problem, the college has a network
problem, or the lab is in serious trouble.
On your first connection to a machine, you are likely to get a 'PuTTY Security Alert' that reads something like:
In the absence of a reason for serious paranoia, you're probably OK hitting 'Yes'.The server's host key is not cached in the registry. You have no guarantee that the server is the computer you think it is. The server's rsa2 fingerprint is: ssh-rsa 2048 66:02:03:ff:e1:71:ca:09:45:6e:11:7f:16:16:a8:sd If you trust this host, hit Yes to add the key to PuTTY's cache and carry on connecting. If you want to carry on connecting just once, without adding the key to the cache, hit No. If you do not trust this host, hit Cancel to abandon the connection.
Now you'll be prompted for your (lab) username and password. That should get you to a shell prompt, just as if you opened a Terminal window when seated at one of the lab computers. Hurrah. That's the first step.
When you are connected in this fashion, you can do anything that you would
be able to do inside a Terminal window. That means you can run
xemacs without the ampersand and edit a
file--provided you can manage to do everything from the keyboard, since
you won't have any of the buttons or menus. Note that it is OK to open
more than one SSH connection from your computer; to avoid confusion,
though, you should make multiple connections to the same lab computer
instead of spreading them around. You can also the Java compiler, and you
can run your Java programs as long as they interact only through the
terminal.
(If you want to work this way, you might try using the editor
pico instead of emacs. It lacks many of
Emacs's nice features, but it always displays a list of available keyboard
commands at the bottom of the screen, and it's OK for doing fairly simple
work.)
When you are finished using a terminal connection, type the command
logout or exit to the shell prompt to end the
session.
To get a full version of the lab desktop environment on your own computer, you will need to get VNC client software for your computer. Once you have that, you'll need to establish a tunnel using SSH for connecting to the lab, and you'll need to start a VNC server on a lab machine.
Pick one of the lab machines and log in using SSH.
The very first time you use VNC in the lab, you'll need to supply an additional password for it. You should pick a different password from the one you use for campus; it should not be obvious, but it does not need to be too complicated, either, because this password only protects your VNC session from other users who have logged onto the same computer. Run the command
vncpasswd
and supply the password you will use. This password is stored under your
home directory; so it will be the same on any of the lab computers.
Assuming that you're still connected to one of the lab machines, you should now be able to run the command
vncserver
Note the first line printed; it should say something like
The number after the colon is important; this is your "display number".New 'X' desktop is cslab04:3
Now you need to use your SSH program to create a tunnel from your
computer to this display on the lab computer. You do this by opening a
new SSH connection from your computer. You'll specify port 5901 as the
local end of the tunnel, and port 5900+x on localhost as the
other end, with x being your display number. (In our example,
that will be display 3, so port 5903).
With PuTTY, you pick "New connection..." and fill in the host name as
before. But before you open the connection, find 'Connection, SSH,
Tunnels' in the tree
of options on the left of the dialog. Fill in 5901 for the
"Source port", and fill in localhost:5903 for the
"Destination". Click "Add", then open the connection.
On Mac OS, you open a new Terminal window and (in our example) type the command
ssh -L 5901:localhost:5903 mserd@cslab04.wheaton.edu
After the -L, the first number is the local port, and the
number after the second colon is the display number plus 5900.
(If is possible to add a tunnel to an already existing connection, and it
is possible to automate some of the connection process. Those tips wlll
be described elsewhere.)
Launch your VNC viewer and connect to localhost:1 (that's
display 1 on localhost). If you've done everything, you should next be
prompted for your VNC password and then, at long last, see your virtual
desktop in a new window.
Your VNC session will keep running until you tell it to log out or someone restarts the computer. That means you can reconnect to it if your connection is interrupted, or if you simply close your VNC viewer and/or your SSH tunnel.
Because your VNC session continues, you do need to remember to log it out when you really are through with it. Some tips on how to find your VNC sessions will be posted elsewhere.
Chicken lets you create the tunnel from inside the program. To do
that, skip the ssh login and just launch Chicken. In the
"VNC Login" dialog, make sure that the Host is localhost
and use the remote display number.
Then check the "Tunnel over SSH" box near the bottom, and put your lab
username and the the host where your server is running in the "SSH
host" box (mortimersnerd@cslab04.wheaton.edu in our example).
Your VNC password goes in the "Password" box; you'll be
prompted for your SSH (lab) password after you hit "Connect".
As a bit of extra protection, the college restricts what campus
computers can be reached from off-campus. As a CS lab user, you can use
SSH to connect to the system csgate.wheaton.edu from
elsewhere on the Internet. From csgate, you can, in turn,
use SSH to connect to one of the lab machines.
To tunnel your VNC session through csgate to a lab machine,
you need to first create a tunnel to csgate, then create
another tunnel from there to the lab machine you want to use; those two
tunnels need a port number to connect them together.
So that we don't all pick the same number, I suggest that you use as
your personal port number what you get when you add your cslab user-number
to 10,000. You can use id -u to find out your user number.
So, for example, if mortimersnerd does that, he sees
His personal port number then becomes 12339.2339
Our user Mortimer should therefore connect to csgate with a tunnel from local (source) port 5901 to port 12339. On Mac OS or Linux, that would use
ssh -L 5901:localhost:12399 mortimersnerd@csgate.wheaton.edu
On MS-Windows, you'll need to configure the tunnel in PuTTY before you connect to csgate (as above, but with your personal port number instead of the VNC port.)
On csgate, you need to complete the path by creating a tunnel from csgate to your VNC server. For our example, Mortimer could connect on to display 3 on cslab04 with
ssh -L 12399:localhost:5903 mortimersnerd@cslab04.wheaton.edu
Finally, he can point his VNC viewer at localhost display :1, which will
be connected to his VNC session on cslab04.