Computing support

Rules and Regulations for Using UCLO Computers, Printing, Remote Login and File Copy

The Observatory has two computer-equipped classrooms and a number of PCs to control our telescopes and astronomical cameras. All classroom PCs are dual-boot and run MS-Windows and Linux (Ubuntu). Their use is governed by rules and regulations. Each classroom has printers for student use. User data is held on a central server and backed up daily. Files can be recovered by the sytem administrator up to six months after deletion.

The Linux-based computing resources at UCLO are accessible over the internet via remote login. If you have any issues regarding hardware or software please contact Thomas Schlichter, the UCLO Computing and Instrumentation Officer.

Please note that misuse by a student may lead to a withdrawal of access.

Printing

All UCLO printers can be accessed from Windows and Linux via the usual print dialogues. Command line printing is available under Linux.

Library Printer:
The Library houses a Xerox AltaLink A3/A4 colour printer and copier, with UNIX print queue name uclo_liblaser for stapled A4 B/W prints. Please see the UCLO system administrator if you need colour printing.

3rd-Year Classroom Printers (South Wing):
The default printer is an A4 black and white laser printer with UNIX print queue name ulo_swlaser.

Printing from the Command Line:
The print system recognises a large number of filetypes and will print them correctly without additional user specification. For example, to print a file named test.jpg from the command line to the laser printer in the library, type:

lp -d uclo_liblaser test.jpg

This will do all the necessary conversions and send the file to the selected printer. If the destination printer is omitted, the file will print on the default printer.

Remote Access to the UCLO Linux Cluster

By default, remote access to all UCLO accounts is disabled, for security reasons. However, any user with a UCLO account can request authorization for remote access by sending an email giving their name and UCLO username to the UCLO 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 UCLO 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 Linux/Unix

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

 ssh -l "your_ulo_username" -C -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 UCLO password.

From Apple Mac OS X

To run X-Window applications remotely on a Mac you need to install XQuartz. To enable remote running of OpenGL applications like 'nightfall' issue the command below in a Mac terminal (put the two lines below on a single line, followed by ENTER): 

defaults write org.macosforge.xquartz.X11 
 enable_iglx -bool true

For XQuartz 2.8.0 and later settings have changed and you should enter this command (again, all on a single line followed by ENTER):

defaults write org.xquartz.X11 enable_iglx -bool true

You can find more detailed and up-to-date information here: https://unix.stackexchange.com/questions/429760/opengl-rendering-with-x11-forwarding.

For logins from machines running OS X, use:

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

From Microsoft Windows

To login from an MS Windows machine you need to have a Secure Shell (SSH) Client (like PuTTY) installed. Enable "X11 Forwarding" before connecting to allow the display of graphical output (select Connection → SSH → X11 and tick the checkbox) .

For graphical output you'll also need an X-Window server running on your machine like XMing; download and install the latest Public Domain Release (currently version 6.9.0.31, direct download link here).

When started, XMing runs in the background and does not open an application window. To check if it's running look for the X-icon in your icon tray.

Running programs remotely

If you plan to do data processing or other compute-intensive tasks please "hop" from UNITY to URANIA by running

 ssh -X urania

This will avoid heavy loads on the UCLO login host UNITY and keeps it responsive for all users. URANIA is configured the same way as the UCLO desktops, but will not be switched off arbitrarily.

 

Remote File Copy:

FileZilla is a graphical user interface for file transfer and can be downloaded and installed on Windows and Mac OS X. On Linux you can usually use the package manager to install it. 

A command line alternative on computers running unix-like operating systems (such as Linux or OS X) is the sftp command:

sftp unity.ulo.ucl.ac.uk

or

 sftp "your_ulo_username"@unity.ulo.ucl.ac.uk

They use SFTP, the Secure File Transfer Protocol.

On MS Windows machines you could also install an SCP client like WinSCP.

Troubleshooting:

Remote login to the UCLO Linux cluster is via Secure Shell (SSH), and is accomplished by connecting to the only UCLO machine accessible from the outside:

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

 The host key fingerprints for UNITY are:

SHA256:

ECDSA:  533TsvOzbC7Lve9jjDOpReinbQx6p9PIKi+CQEx4lgY  root@unity
ED25519:ajoYFoDhqKCNu0G8K4polcM9CIbqpxH54v6jOusYQug  root@unity
RSA:    QnhERucbznqWLdAGyS86ieNgvhe0a8yVz7IfSzDx9mM  root@unity

MD5:

ECDSA:  9d:62:c6:7c:d7:95:7e:34:3b:65:27:d6:9a:9f:d2:ac root@unity
ED25519:d7:1b:c1:e9:5a:34:63:f9:52:7b:91:09:a5:3b:dc:0b root@unity
RSA:    3d:26:3e:bb:20:67:db:5a:17:02:e0:46:9c:7d:81:56 root@unity

To enable access, you might need to edit your ssh "known hosts" file, if you get error messages and can't log in.

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 3d:26:3e:bb:20:67:db:5a:17:02:e0:46:9c:7d:81:56.
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 time 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 UCLO system administrator for advice before proceeding.

An explanation of how SSH works can be found at  https://www.ssh.com/ssh/.

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 UCLO system administrator and he will try to help to resolve the problem.

Please include your name, username and the date and time when you tried to connect , the following in the email:

•  Your name, username and the date and time when you tried to connect,
• the type of operating system of your machine (Linux, Apple Mac, Windows),
• the terminal output produced by ssh or the putty error message as text attachment (ideally) or screen shot.

Please do NOT send your password via email - this will result in your account being locked and a new password being issued - UCL will NEVER ask you for your password.

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

Acessing data on the UCLO Linux server from UCLO Windows PCs

All telescope data is archived on the central Linux server. To access this data from UCLO desktops running Windows connect to urania.ulo.ucl.ac.uk (128.40.167.10) via WinSCP or FileZilla.

The Asteroid Cluster at Physics in Gower Street

The Asteroid cluster is operated by the Department of Physics and Astronomy and provides Linux-based computing facilities to the Department's undergraduate students. Access priority is given to MSci students working on final-year projects.

The cluster terminals are located in room A19 in the Physics Building.

The principal source of information is the department's Asteroids Cluster page.