Accessing a cluster

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This section uses the wiki's documentation conventions.

Use a secure shell program/client (SSH) to connect to the cluster and a secure file transfer program to move files to and from the cluster.

There are many suitable secure clients for Windows, Mac OS X, and UNIX/Linux. We recommend PuTTY and Xming for Windows users. Macintosh and UNIX/Linux users can use their pre-installed SSH and X11 software. (Newer versions of Mac OS X may not have a current version of X11 installed. See the Apple web site for X11 installation instructions.)

IT strongly recommends that you configure your clients as described in the online X-windows (X11) and SSH documents (Windows / Linux/MacOSX).

Your HPC home directory has a .ssh directory. Do not manually erase or modify the files that were initially created by the system. They facilitate communication between the login (head) node and the compute nodes. Only use standard ssh commands to add keys to the files in the .ssh directory.

To initiate an SSH connection from a Mac/UNIX/Linux system to the cluster's login (head) node, use the generic command

ssh«options» «HPC_username»@«HPC_hostname»

For example,

    ssh -Y traine@mills.hpc.udel.edu

This ssh command is on your local system. This example assumes you have a local command line interface, and have an X11 server running, for example, Mac/UNIX/Linux or cygwin/X (with the openssh client)

Windows with PuTTY/Xming: When using the recommended PuTTY/Xming on Windows installation instructions, you create a saved session with the options to want to use every time you logon. You can create as many saved sessions as needed with various options.

Mac/UNIX/Lunix with command line SSH: When using the recommended setup for command line SSH, you can add a service that bundles options you want to use every time you logon or copy files. You can add as many services as needed with various options.

When an ssh session is ended intentionally or by a loss of connectivity, you cannot generally restart it and resume your work. The UNIX screen command provides a useful solution. This command creates a virtual terminal window session that continues to run after you are logged off. It allows you to reattach the same virtual terminal window session and resume working. See the man page for screen for details.

Suppose you have a significant amount of interactive work to be done on the cluster, but you have a interruption coming up shortly, such as lunch. You can start a screen session and work until lunchtime. Log out and when you come back from lunch, reattach the screen session and continue your work. Even output from jobs will be displayed, as if you never left.

If you are using an unstable network connection, for example, a laptop that drops your connection when it sleeps, you may want to start a screen session before you lose connectivity.

Accessing a cluster

Secure shell program (SSH)

Logging on the cluster

Screen sessions

hpc documentation