Text-mode access using OpenSSH#
Prerequisite: OpenSSH#
Before connecting with OpenSSH, make sure you have completed the following steps:
Create a public/private SSH key pair, which will be used to authenticate when making a connection.
Apply for a VSC account and upload your public SSH key to the VSC accountpage.
Link your private key to your VSC-id in your SSH configuration file at
~/.ssh/config.
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 [email protected]
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 [email protected]
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 configuration file ~/.ssh/config can be used to configure your SSH
connections. For instance, to automatically define your username, or the
location of your key, or add X forwarding. See below for some useful tips to
help you save time when working on a terminal-based session.
Managing keys with an SSH agent#
It is convenient to use an SSH-agent to avoid having to enter your private key’s passphrase all the time when establishing a new connection.
Proxies and network tunnels to compute nodes#
Network communications between your local machine and some node in the cluster other than the login nodes will be blocked by the cluster firewall. In such a case, you can directly open a shell in the compute node with an SSH connection using the login node as a proxy or, alternatively, you can also open a network tunnel to the compute node which will allow direct communication from software in your computer to certain ports in the remote system.
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_vsc.
The second thing to check is that your
private key is linked to your VSC-id
in your SSH configuration file at ~/.ssh/config.
If your private key is not stored in ~/.ssh/id_rsa_vsc, you need to adapt
the path to it in your ~/.ssh/config file.
Alternatively, you can provide the path as an option to the ssh command when
making the connection:
$ ssh -i <path-to-your-private-key-file> <vsc-account>@<vsc-loginnode>