Further connection options¶

Prerequisites¶

To connect to the cluster, you need to use a terminal application. These are available on Linux and MacOS but may require configuration or installation on Windows. See the relevant section of the ScienceCloud Training Handout for more detail.

Login nodes¶

After running ssh -l shortname cluster.s3it.uzh.ch, the load balancer redirects the requests in round-robin fashion to one of the several login nodes.

Passwordless authentication¶

First, create an SSH key on your local laptop/computer using

ssh-keygen -t rsa -b 4096

Then, once you have located the public key that you just created (if you use the default name, it will be called id_rsa.pub located in the ~/.ssh folder), you will need to add this key to the authorized_keys file on ScienceCluster. You have 2 options when doing so:

Option 1: Use ssh-copy-id from your client¶

You can use ssh-copy-id to add the public key.

From Mac or Linux:

ssh-copy-id -i ~/path/to/local/your_public_key_name.pub shortname@cluster.s3it.uzh.ch

This will add the public ssh key to ScienceCluster, stored as a new line in the file ~/.ssh/authorized_keys.

Option 2: Use a terminal-based text editor from the server¶

Using a terminal-based text editor to edit the authorized_keys file is also an option if you prefer a more manual approach.

First, it is suggested to make a backup of the existing authorized_keys file (if there is one), in case you make any errors during this process.

cp ~/.ssh/authorized_keys ~/.ssh/authorized_keys_copy

If there is no current authorized_keys file on ScienceCluster, you can create a new file with the the nano text editor:

nano ~/.ssh/authorized_keys

This command will open the Nano text editor and allow you to edit the new authorized_keys file. It is important to note: each line of the authorized_keys file is a public ssh key.

To add a new public ssh key, simply move the cursor to a new line and paste the desired public ssh key. When you are finished, exit the nano editor with CTRL+x. To confirm type y then ENTER.

For reference, you can print the value of your public key if you run cat ~/.ssh/your_public_key_name.pub from the laptop/computer where you generated the key pair. The entire printed value will be what you copy/paste into the ~/.ssh/authorized_keys file on ScienceCluster.

Verify a new public ssh key¶

Once you have added the public ssh key to the authorized_keys file, you should be able to access ScienceCluster using:

ssh -i ~/.ssh/your_private_key shortname@cluster.s3it.uzh.ch

Problem solving¶

I set up my ssh key pair but I still can't log in¶

A common issue with the key authentication is incorrect permissions on the home directory, .ssh directory, or the .ssh/authorized_keys file on the server. The home directory should be writeable only by the owner while the other two should be accessible only by the owner. You can set the correct permissions by connecting via ssh to the server and running the following commands:

chmod 750 $HOME
chmod 700 $HOME/.ssh
chmod 600 $HOME/.ssh/authorized_keys

If you aren't prompted for your password, try this command:

ssh -o PubkeyAuthentication=no -o PreferredAuthentications=password shortname@cluster.s3it.uzh.ch

I get an error message saying "Remote host identification has changed"¶

Run the following command, which will update your file ~/.ssh/known_hosts

ssh-keygen -R cluster.s3it.uzh.ch

Requesting support¶

Please add -vvv to your ssh command, which prints a verbose output. For example,

ssh -vvv shortname@cluster.s3it.uzh.ch

and contact Science IT with the output as text or a screenshot.