FAQs

How do I access the HPC Cluster?

You can remotely access the frontend machines astro01-09 via SSH to submit jobs or to analyze data (see Hardware for an up to date list of available frontends). For example, you can login to the astro06 machine entering the following in the command line

ssh username@astro06.hpc.ku.dk

From which you will be prompted to enter your password (Note: If the connection times out, it's likely that your IP address is not recognised). By entering the correct password, you will arrive at your home directory /groups/astro/username. It may be a good idea to check the load factor after logging in, using "top", and choose a different frontend if the CPU or memory use is already high (use "<" or ">" in top to temporarily change from sorting on CPU to memory / virtual memory).

You can cut this down to

ssh astro06

by adding these lines to the file ~/.ssh/config:

Host astro06        
    User username        
    HostName astro06.hpc.ku.dk

Do not use the ssh option -Y, which "enables trusted X11 forwarding". This means, basically, that you turn off some essential X security features and say "I trust the remote host completely". Forwarding of X should work without any extra options.

Passwordless ssh login:

You can avoid to type in your password each time for the authenticating of SSH sessions, by using an SSH key with the RSA or DSA encryption, in combination with ssh-add and ssh-agent. Therefore, you generate with ssh-keygen on your local laptop/computer a pair of a personal (id_rsa) and public key (id_rsa.pub).

ssh-keygen -t rsa

With the option -t you specify the encryption type. Here we use RSA, but you can also use DSA. You will asked for the filename, you can just press enter and use the default. Then, you will be asked for a passphrase to protect your personal key. You should NOT under any circumstances use an empty pass phrase; it is not necessary for convenience reasons (see below), and could endanger your access to remote supercomputers. Use instead really a "pass phrase"; a relatively long expression, which need not have the character of a password (such as "I really love Putin" or something equally ridiculous ;-). There will be stored two keys (id_rsa and id_rsa.pub) in the hidden folder ~/.ssh/ on your client (laptop or remote host you want to be a client of another host). You need to copy your public key to the accepted key list of on your host machine (authorized_keys).

cat ~/.ssh/id_rsa.pub | ssh username@astro06.hpc.ku.dk 'cat >> .ssh/authorized_keys'