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Durham University


Getting a COSMA account

To get a new COSMA account, you need to apply via the DiRAC SAFE system:

When creating your account, it is essential that you upload an ssh key. You should also select the project to which you will belong. This will either be a DiRAC project, or if you are a local Durham user (for COSMA5), please select project hpcicc. Once this form has been submitted, you will then have to wait for COSMA staff to create your account. You will be notified by email.

Detailed instructions are available here

You will need an ssh key.

Generating a SSH key

Authentication requires an SSH key pair. A key pair has two parts:

  • A private part (keep this very safe)
  • A public part (give this to COSMA - or anything else)

SSH uses public key cryptography. When you try to connect, COSMA will use the public key to generate a "challenge", an encrypted message. Only the private key can decode this. Your computer then sends the correct response to COSMA, and access is then granted.

On Linux, or a Mac, to generate a key pair, you can use:

  • ssh-keygen -t ed25519 -C "unique name to identify this key." (e.g. -C cosmaKey)

If that fails (probably you have an old ssh client), you can try:

  • ssh-keygen -t rsa -b 4096

On Windows, please follow these instructions.

This will ask for a passphrase: PLEASE use a strong one, as the use of a user with a weak passphrase was responsible for the hacking of HPC systems across Europe, China and the USA in 2020. Something like 16 characters would be good.

It will also ask for a location. You can use the default, or something else, e.g. ~/.ssh/id_rsa_cosma.

This will create:

  • id_rsa - the private part. Keep this safe, and consider where it is backed up to (e.g. don't back it up to the "cloud"), and don't copy it to other systems. Also NEVER send it by email anywhere.
  • - the public part. Upload this to SAFE.

cosma-support will then add your key to the system (so it might take a few minutes, depending how busy we are).

To avoid having to enter your passphase every time you ssh to COSMA, you can use an ssh-agent. e.g. in your local .bashrc file, you can put something like: eval $(keychain --eval /path/to/id_rsa 2> /dev/null)

Note, you can use the same public key on other systems, e.g.,, github, etc, provided the private part remains on your system.

SSH from Android

On Android, use e.g. JuiceSSH. You will need to generate a key pair on the app.

SSH on Windows

Windows 10 includes the ssh-keygen utility, so keys can be generated as above. However, if not using WSL, a tool such as Putty will be required.


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