If you login on a non-Athena computer connected to the Internet, you can
use Athena by connecting to one of our dialup servers over the network.
You can also connect to a private athena workstation, if you have the
permission of the maintainer.

Because you will have a faster connection to these machines than users
with modem connections, you must remember that you are sharing the
machines and not abuse this privilege.  None of the dialup machines
should be used for jobs that are excessively long or computationally
intensive.  If you want to run such a job on athena, you should probably
come to campus and log into a workstation in one of the clusters.

Use an encrypted telnet, or ssh, on your system to connect to
"athena.dialup.mit.edu" or to "express.dialup.mit.edu" if you are only
going to be connected for a short time (see the answer "Accessing
DIALUP EXPRESS" under the Dialup topic for more information on dialup
express).  The dialup machines are currently Sun UltraSparc's.  If you
are connecting to a private workstation, you should use the name of
that machine, instead of athena.dialup, or express.dialup.

The dialup machines no longer accept unencrypted connections (such as
those made by the default Windows telnet application).  However, you may
enconuter private workstations that do accept unencrypted connections.
It is strongly discouraged to use an unencrypted telnet, because this
sends your username and password in the clear, for any malicious user on
the network between you and the target machine to read.  (See the answer
"Why should I use ENCRYPTION" for more information). 

Neither athena.dialup nor express.dialup will allow you to run any X
applications, or open other windows.  If you want to log in to Athena
remotely and use Xwindows, you have two options:

1. Log into a private workstation that you have access to.

2. Log into x.dialup.mit.edu.  This is the only portion of the dialup
   pool which supports windows.  The load on this machine is likely to
   be very high, even with only a few users on it.
 
In order to display windows from a workstation or a dialup to which
you have logged in remotely on the X server you are using, you have to
do the following:

1. On the local computer, startup the X server program and tell it to
accept connections from the localhost. On unix systems, this is the
default, and should also be the default on most Mac and Windows based
X servers.

2. Connect to the remote host using SSH. You should make sure that X
connection forwarding (often called X11 forwarding) is enabled. On
Openssh, if it isn't configured by default, one would have to connect
using the -X option. On the Windows and MacOS based ssh clients
(securecrt, putty, niftytelnetssh, etc.), there should be a
configuration option.

For more information, see the stock answer Connecting to DIALUPS with SSH.

Now you should be all set -- any X window commands that you run on the
remote host or dialup should display on the local computer's X display.

Things that might go wrong:
--------------------------
If you get an error like the following: "xterm Xt error: Can't open
display: :" or "xev: unable to open display ''", it's likely that
either an X connection wasn't made or your DISPLAY environment
variable wasn't set properly. To determine the current value of the
DISPLAY environment variable, type at the athena prompt:

echo $DISPLAY

It should look something like this

REMOTE-HOST:n.0

where REMOTE-HOST is the machine you have logged into, and n is an integer,
that changes each time you login.

If it is blank, then it's likely that the machine you're logging into
doesn't support running X programs, your ssh client isn't currently
configured to run X programs, or your local x server is not running.

If it isn't blank but doesn't show something like REMOTE-HOST:n.o,
then you make sure that you aren't manually setting the DISPLAY
environment variable in your configuration files.

last updated: July 26, 2002