Remote Access


If you exceed three failed remote authentication attempts (within a 10 minute window) the system will ban your IP address from further attempts for the next 30 minutes.

The cluster can be accessed via SSH (see Getting Connected) with only password authentication so long as you are connecting via a Supported Organisations network address.

To connect from remote addresses, we require using a cryptographic authentication instead of a password. For this authentication method you need to generate an SSH key pair.


You can see why it’s critical that we enforce key use for remote access by looking at the number of rogue access attempts on our login tracker at

SSH key pairs consist of two individual parts: a private and a public key. The private key must always be kept secret, much like a password. The public part, however, may be transported (as the name says) publicly and will be installed on gruffalo. Your private key will then be used to verify your access.

The following steps will show you how to generate a key pair and how to install it. If you already have a key pair, you can skip straight to the installing section.

Generating a key pair


Use your own PC/laptop to generate your key pair - don’t run these instructions on gruffalo.

The tool ssh-keygen can be used to generate an SSH key pair. For further details about its usage, please refer to the ssh-keygen(1) manual page.

If no parameter is specified on execution, ssh-keygen will create an RSA key, but Ed25519 keys are a better choice for gruffalo, which can be generated using the following command:

$ ssh-keygen -t ed25519
Generating public/private ed25519 key pair.
Enter file in which to save the key (/home/dvader/.ssh/id_ed25519):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/dvader/.ssh/id_ed25519
Your public key has been saved in /home/dvader/.ssh/
The key fingerprint is:
SHA256:EQNnu/70ehGip3Ki1ghuqFTsEB7JpzDubsgzKTx0uTs dvader@localhost
The key's randomart image is:
+--[ED25519 256]--+
|      ..=        |
|. .    o +       |
|o= .    o        |
|+.*      o. .    |
| = o.   S. . .   |
|..=o   .. . .    |
|==oo.o  .o.  .   |
|*OoEo + oo ..    |
|=o+o+. +  oo.    |


It is critical that you protect your private key with a passphrase, and ideally ensure the disk it’s kept on is encrypted and that no-one else is ever given access to it. Remember, it’s your private key. Only the public half will be installed on gruffalo.

The keypair will be written to ~/.ssh/ on your local machine and consists of two files: the private key file and the public key-file:



If you provided a custom name for your key, you may find it wasn’t created within ~/.ssh. You can either rename/move the file to match the above, or use the ssh -i option to let SSH know where to find your private key.

Installing your public key


If you are working from home or away from a Supported Organisations network, then you won’t be able to install your public key using these instructions. Instead, you can email it to us (see Contact Us and we’ll get it installed for you.

To install your public key, visit


Depending on your browser, you may initially see a popup box prompting for your username and password. Ignore it, hitting Cancel or Escape until you see the screen below.

Log in using your username and password.


It should default to showing you the details of your account, so scroll down until you see the section marked SSH public keys:


Next, click Add and then paste your public key into the box that appears:


Close the popup by pressing Set, then scroll back to the top of the page and select Save to confirm your changes.

Connecting remotely

You can now test your key by attempting to connect to gruffalo and issuing a command. You should be asked for your private key’s passphrase rather than your user account’s password:

$ ssh <username> whoami
Enter passphrase for key '/home/dvader/.ssh/id_ed25519': [Passphrase]

If you manage to log in successfully, then you should be good to connect from anywhere. Excellent!


If have problems, try connecting with ssh -vvv which will produce lots of debug output and may give some hints as to where things are going wrong.

Additional notes

Many locations, including other institutions or public locations (airports, cafes, etc) may restrict which ports outgoing internet traffic can use, often locking it down to just a small subset that is enough for email and basic web access.

SSH uses port 22 by default, but if you find your connection to gruffalo being blocked, it’ll also accept connections on port 443, which is normally used for encrypted web traffic and therefore usually available. You can tell SSH to connect this way by passing -p 443 as an extra parameter, or by editing your ~/.ssh/config file to include the following:

Host gruffalo
  Port 443
  Username <username>


Only the most evil of deep-packet inspection (DPI) firewalls are likely to block SSH over port 443, so if you’re going to connect remotely a lot it’s probably worth setting port 443 as your default.