UKy HPC Frequently-Asked Questions

1.1. What do I need to do before I can login ?: First, you must obviously have an account. For detailed information on user account policies pertaining to the UK HPC computing resources see the Computer Use Policies section of this website. To obtain an online (pdf) account application form, see the Account Information section of this website.

You must use a secure shell ( ssh ) client on your computer.
1.2. What is secure shell (ssh)?: See the SecureAccess/ssh page.
1.3. Is it absolutely necessary for me to use secure shell for login ?: Yes. See the SecureAccess/ssh page.
1.4. How can I obtain a secure shell client if I do not currently use secure shell (ssh) on my computer ?: See the SecureAccess/ssh page.
1.5. May someone else login under my account as long as they have my permission to do so ?: No. The only person who may use a given account is the person to whom that account was granted. Permitting any other person to use your account may result in the suspension of your computing privileges. For more information on account restrictions or other user policies. See the Computer User Policies section.
1.6. Can I connect with an XDM/CDE session?: CDE sessions are no longer permissible for security reasons.
1.7. How do I login and run X applications, etc?: You will need an ssh client for your local machine if you do not already use one. For more info, see SecureAccess/ssh . For security reasons, it is important to use an X connection that is encrypted by your ssh connection (refered to as a "tunneled" connection). This is important so that others cannot spy your important information such as passwords, etc.

Enabling an encrypted X connection over ssh depends on the proper client settings. For Linux clients, your client may be configured globally by default to setup forwarded X connections; or you may override the default with the -X command-line flag or specify this on a per-host basis in your own configuration file. See the ssh man page for more info.

For MS-Windows clients, there is often a check-box in the session setup for X forwarding. This may be on a global basis or a per-host basis.

You will notice if your X connection is being proxied by ssh by checking your DISPLAY variable. If it is set to the host machines IP number (as opposed to your local machine), the connection is being proxied by ssh.

For more info about forwarding X11 connections with ssh clients such as puTTY, see this page . Note: this is an off-site link and could disappear without notice.
1.8. How do I tell if my ssh connection is ready to proxy/tunnel an X11 connection?: X11 sessions that are not tunneled with encryption, such as with ssh, can be insecure. If your ssh client is configured to request X11 forwarding, the SDX ssh server is configured to automatically set the DISPLAY variable for you to forward X11 packets. The DISPLAY variable will be set to the IP/hostname of the remote machine (not your local machine's IP).

Example:

echo $DISPLAY
128.163.15.11:10.0

where 128.163.15.11 is the IP of the remote machine (ie the ssh proxy).
1.9. I am having trouble with X connections and the xwin32 software. Can you help?: Starnet Communications, the vendor for the xwin32 X software for Windows, maintains a FAQ .

Look/search for the SSH entry.

FAQ generated by: makefaq

Table of Contents

1. Logging in