Text-mode access using OpenSSH

Prerequisite: OpenSSH

You will need a public/private key pair to request and account, this key pair has to be used to authenticate when making a connection. For information on how to create a key pair, see the page on generating keys.

How to connect?

In many cases, a text mode connection to one of the VSC clusters is sufficient. To make such a connection, the ssh command is used:

$ ssh <vsc-account>@<vsc-loginnode>

Here,

  • <vsc-account> is your VSC username that you have received by mail after your request was approved, e.g., vsc98765, and

  • <vsc-loginnode> is the name of the login node of the VSC cluster you want to connect to, e.g., login.hpc.kuleuven.be.

You can find the names of the login nodes for the various clusters in the sections on the available hardware.

Note

The first time you make a connection to a login node, you will be prompted to verify the authenticity of the login node, e.g.,

$ ssh vsc98765@login.hpc.kuleuven.be
The authenticity of host 'login.hpc.kuleuven.be (134.58.8.192)' can't be established.
RSA key fingerprint is b7:66:42:23:5c:d9:43:e8:b8:48:6f:2c:70:de:02:eb.
Are you sure you want to continue connecting (yes/no)?

How to connect with support for graphics?

On most clusters, we support a number of programs that have a GUI mode or display graphics otherwise through the X system. To be able to display the output of such a program on the screen of your Linux machine, you need to tell ssh to forward X traffic from the cluster to your Linux desktop/laptop by specifying the -X option. There is also an option -x to disable such traffic, depending on the default options on your system as specified in /etc/ssh/ssh_config, or ~/.ssh/config.

Example:

$ ssh -X vsc98765@login.hpc.kuleuven.be

To test the connection, you can try to start a simple X program on the login nodes, e.g., xeyes. The latter will open a new window with a pair of eyes. The pupils of these eyes should follow your mouse pointer around. Close the program by typing \”ctrl+c": the window should disappear.

If you get the error ‘DISPLAY is not set’, you did not correctly enable the X-Forwarding.

How to configure the OpenSSH client?

The ~/.ssh/config file can be used to configure your SSH connections, e.g., to automatically add X forwarding or specify the path of a key that is not in the default location. We provide some useful tips.

Troubleshooting OpenSSH connection issues

When contacting support regarding connection issues, it saves time if you provide the verbose output of the ssh command. This can be obtained by adding the -vvv option for maximal verbosity.

If you get a Permission denied error message, one of the things to verify is that your private key is in the default location, i.e., the output of ls ~/.ssh should show a file named id_rsa.

If your private key is not stored in a default file (~/.ssh/id_rsa) you need to provide the path to it while making the connection:

$ ssh -i <path-to-your-private-key-file> <vsc-account>@<vsc-loginnode>

Alternatively, create aan SSH configuration file.