SSH access

COSMA has 7 login servers:

  • COSMA5: login5a, login5b

  • COSMA7: login7a, login7b, login7c

  • COSMA8: login8a, login8b

To connect to COSMA, you will need to generate a SSH key pair, and upload the public part to SAFE. You should protect your ssh key with a good passphrase. In addition to this, you will also need to know your COSMA password, which should obviously be different from your sshkey passphrase. A single SSH keypair will be able to connect to all login nodes. Please note that each login node has a separate fingerprint, which will cause a warning and prompt you to accept it the first time you try to log in.

The same SSH keypair can also be used for git access (for example, see this guide for GitHub).

If you forget your sshkey passphrase, you will need to generate a new key and upload it to SAFE.

If you forget your COSMA password, you can reset it on SAFE.

Logging in with SSH

If you have done that already, use SSH to connect:

ssh (where XX is the COSMA you are logging in to)

You may need to specify your ssh key:

ssh -i /path/to/ssh/key

where USER is your COSMA username. This will log you in via a secure shell to COSMA. You can login to different COSMAs by specifying a different login node: for COSMA5

  • for COSMA8

  • for COSMA7

  • for COSMA5

  • etc.

The generic loginX given here will then randomly (round-robin) select a specific login node (e.g. login7 will put you on one of login7a, login7b or login7c).

The login systems are also the developing nodes: so they know about the compilers, have access to modules, and the batch system. Unless otherwise specified, all of your interactive work should be done on the login nodes. For instructions on how to submit jobs to the batch quees, see slurm. You can submit jobs to any batch queue from any login node, and access all the storage from any login node.

You will then be asked to enter your ssh key passphrase (if you run a key manager, you’ll only have to do this once per reboot), and after that, enter your COSMA password.

If you forget your ssh key passphrase, you will need to generate a new key and upload it to SAFE.

If you forget your COSMA password, you can request a reset on SAFE. In this case, when you log in, you will need to enter the new password twice (once to log in, once to begin the password reset process), followed by a new password of your choice (twice).

To request a password reset on SAFE, select “Login accounts” -> “USER@cosma” and then click the “Request Password Reset” button. A new ssh key can also be uploaded on this page.

Cannot get access?

If you are receiving permission denied when trying to access COSMA, it could be:

  1. You need to specify your ssh key, e.g. ssh -i /path/to/ssh/key user@login*

  2. You need to update your ssh key on SAFE (and then wait for cosma-support to accept the new key)

  3. You have forgotten your sshkey passphrase or your COSMA password.

  4. The permissions on your key, or directory containing it are wrong.

  5. You have forgotten your COSMA password (different from your ssh passphrase). You can reset this on SAFE (and then wait for cosma-support to accept the password reset request)

  6. You are using a banned key type upload a new one to SAFE

  7. You have entered your password wrongly too many times and have been temporarily banned (typically 15 minutes)

If you need to generate a new ssh key, there is some info here.

For other reasons, please contact cosma-support.

Running programmes with graphical interface

If you wish to open a graphical programme on a login node (i.e. to view a plot in python, open a PDF in an evince viewer or a picture in eog, view an HDF5 file in hdfviewer, etc.), you need to add -X flag to forward the X server:

ssh -X

You should then be able to have programmes forwarded to your local X server. For instance, typing

eog PICTURE.png

on a COSMA login node will open the file.

This should works out of the box on most Linux / BSD systems. If you are using macOS, you will need to install XQuartz on your machine.

For many applications, x2go is a better way of getting a graphical interface. See the x2go pages for more information. It will provide you with a graphical COSMA desktop. This is more responsive than X11, and is the recommended way of accessing COSMA graphically.

Saving SSH Configuration

To save yourself from typing the full command every time, you can save your SSH configuration in a ~/.ssh/config file on your local machine. For instance, if your configuration file looks like this:

Host cosma
 User USER
 IdentityFile ~/.ssh/id_rsa
 ForwardX11 yes


ssh cosma

will be equivalent to

ssh -X

To learn about more advanced options, please refer to the manual: man 5 ssh_config.

Reusing SSH connections

To avoid entering passwords too many times, you can multiplex your ssh connection.

To do this, you need to add something like:

ControlPath ~/.ssh/controlmasters/%r@%h:%p
ControlMaster auto
ControlPersist yes

to your .ssh/config file, and create the .ssh/controlmasters directory.

Any new connection will then use the first conneciton.

Disk Usage

Your home quota is usually 10 GB. The contents of your $HOME are backed up every night, and should only be used for code and small datasets that are not easily recoverable.

All generated/large datasets should be stored in a separate space, located in /cosma[5678]/data/project_name/USER. Your quota there is more generous and is currently set by default to 10 TB.

COSMA8 / COSMA7 / COSMA5 Differences

Due to differences in CPU architecture between COSMA5, 7 and 8, code compiled with strong optimisation on the COSMA7 login nodes may not work on the COSMA5 or 8 compute nodes, throwing illegal instructions errors. Therefore, please try to use COSMA5 login nodes to compile code for these queues, or add a recompilation step to your submission script.