Remote Access to the ULO Linux Cluster

By default, remote access to all ULO accounts is disabled, for security reasons. However, any user with a ULO account can request authorization for remote access by sending an email giving their name and ULO username to the ULO system administrator. You will normally then be added to the list of remote users within a day or two (and will be sent an email confirmation when this has been done).

[Please note that ULO accounts are normally only available for students undertaking coursework at the Observatory; and that only the GNU/Linux system – not Windows accounts – can be accessed remotely.]

Remote Login

From unixy machines

To login from a Linux machine, type in the following at the command line:

 ssh -l "your_ulo_username" -X unity.ulo.ucl.ac.uk

(where, of course, you should substitute the appropriate value for "your_ulo_username"). You'll then be prompted for your ULO password.

For logins from Apple machines running OSX, use:

 ssh -l "your_ulo_username" -Y unity.ulo.ucl.ac.uk

From Microsoft Windows

To login from an MS Windows machine you need to have a Secure Shell Client (like PuTTY) installed.

If you want more than just a terminal window – e.g., if you want to open a graphics window – you'll also need an X-windows server (such as XMing). In this case it's important to enable SSH Client "X11 Forwarding", otherwise applications cannot open a display window on your machine. Installation instructions for XMing can be found here.

Remote File Copy

To copy files between computers running unix-like operating systems (such as linux or OSX), use the sftp ('secure file transfer protocol') command; for example:

 sftp unity.ulo.ucl.ac.uk    (or:  sftp "your_ulo_username"@unity.ulo.ucl.ac.uk)

On an MS Windows machine you need to install an SFTP client like WinSCP.

Troubleshooting

As should be evident from the foregoing, remote login to the ULO Linux cluster is via the so-called Secure Shell, and is accomplished by connecting to the only ULO PC accessible from the outside:

 unity.ulo.ucl.ac.uk (128.40.167.12)

 RSA: 6d:2c:06:b4:88:75:a0:57:77:55:0d:9d:40:35:35:0a root@unity
 DSA: 26:51:dc:d6:e9:d5:5c:64:e0:4e:2d:22:3d:b0:88:74 root@unity

If your ssh program reports a key mismatch in the "known hosts" file it will also show the file name and the line number of the key entry. Delete this line from the file, start a new ssh connection and wait for ssh to report an unauthenticated host:

The authenticity of host 'unity (128.40.167.12)' can't be established.
RSA key fingerprint is 6d:2c:06:b4:88:75:a0:57:77:55:0d:9d:40:35:35:0a.
Are you sure you want to continue connecting (yes/no)?  

If the fingerprint matches one of the two for UNITY listed above, you can answer with yes and the new host key will be added to your "known hosts"-file.

Usually you only get this message the first you connect to a new host or after a key change. If this happens at any other time there might be an attempt of a "Man-in-the-Middle" attack and you should contact the ULO system administrator for advice before proceeding.

A good background explanation for the procedure can be found at www.securityfocus.com/infocus/1806.

Other problems

If you encounter any other problems, run the ssh (or sftp) command again, but with the -vvv option; this produces 'verbose' output which might give you an idea of what went wrong. If you still can't resolve the problem, email the output to the ULO system administrator and he will try to help to resolve the problem.

Please include the following in the email:

• Your name, username and the date and time when you tried to connect,
• the name of the machine from which you tried to connect (type hostname and copy the output into the email),
• the name of the ULO machine you tried to connect to (it had better be unity!,
• your ssh client's name and version number (type ssh -V).

Please note that remote-login problems can have a wide range of causes and might take some time to get resolved.