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Access and Login

Connecting to the HPC Clusters (SSH Guide)

Once you have registered for your central identity and your PI has added you to an active Allocation in the ColdFront Portal, you are ready to connect to the HPC clusters.

Prerequisite Check:

  1. Allocation Status: If you receive an "Access Denied" error, check that your ColdFront allocation is approved and active.
  2. SSH Key Authentication: Access to the HPC clusters is strictly via SSH Keys. Password authentication is disabled for SSH connections. You must generate an SSH key pair and register your public key before connecting.

Generating SSH keys

In order to generate a SSH key pair follow the below steps:

Linux/Mac

Create a public and private key pair using the following command:

ssh-keygen

You will be prompted for a filename for saving the private key. You should press Enter to use the default name: /home/username/.ssh/id_rsa You will be prompted for a passphrase to protect your private key which you will also confirm. ALWAYS use such a passphrase to protect your private key. ssh-keygen will then create a private and public key. The public key will have a .pub extension (e.g., id_rsa.pub)

Windows

Using PuTTYgen
  1. Download the PuTTYgen tool here
  2. Run the tool executable (puttygen.exe)
  3. Click Generate
  4. Move your mouse over the blank area
  5. Add a passphrase to your key in the Key passphrase and Confirm passphrase boxes.
  6. Save your key pair by clicking the Save public key and Save private key buttons. The private key will have a .ppk extension (e.g. private_key.ppk)
Using OpenSSH

First check if the OpenSSH client is installed.

  1. Open the Settings panel, then click Apps.
  2. Under the Apps and Features heading, click Optional Features.
  3. Scroll down the list to see if OpenSSH Client is listed.
  4. If it's not, click the plus-sign next to Add a feature.
  5. Scroll through the list to find and select OpenSSH Client.
  6. Finally, click Install.

Then open the OpenSSH client and proceed with the key generation:

  1. Press the Windows key type cmd.
  2. Under Best Match, right-click Command Prompt. Click Run as Administrator.
  3. If prompted, click Yes in the Do you want to allow this app to make changes to your device? pop-up.
  4. In the command prompt type: ssh-keygen
  5. By default, the system will save the keys to C:\Users\your_username.ssh\id_rsa. You can use the default name, or you can choose more descriptive names. This can help distinguish between keys, if you are using multiple key pairs. To stick to the default option, press Enter. Note: If a file with the same name already exists, you will be asked whether you want to overwrite the file.
  6. You'll be asked to enter a passphrase. Enter a safe passphrase.
  7. The system will generate the key pair, and display the key fingerprint and a randomart image.
  8. Open your file browser.
  9. Navigate to C:\Users\your_username.ssh.
  10. You should see two files. The identification is saved in the id_rsa file and the public key is labeled id_rsa.pub. This is your SSH key pair.

Note: Normally, the public key is identified with the .pub extension. You can use Notepad to see the contents of both the private and public key.

The HPC Login Nodes

The table below lists the login hostnames for our systems.

System Hostname Status
Aphroditi front01.hpcf.cyi.ac.cy Primary

Note: The hostname front01.hpcf.cyi.ac.cy is the current access point for Aphroditi, but it may be updated to aphroditi.hpcf.cyi.ac.cy in the future. Documentation will be updated when this change occurs.

Important: Login nodes are strictly for compiling code, submitting jobs to the Slurm scheduler, and managing files. Do not run heavy computational tasks on the login nodes, as this disrupts the system for all users.

Connecting to the Clusters

Choose the method that works best for your workflow.

Option 1: Native SSH (Terminal)

If you prefer a terminal, use the standard SSH client installed on your system.

Linux/Mac

If your private key is stored in your .ssh folder in your home directory: $ssh username@hostname

If the key is stored in another directory: $ssh -i /key_path/id_rsa username@hostname

If you encounter a problem with your key permissions, go to the directory where the key is stored and do the following: $chmod 600 .ssh/id_rsa

Windows

You can use the native OpenSSH client (available in PowerShell/Command Prompt) or PuTTY (legacy).

Using OpenSSH:

  1. Open PowerShell or Command Prompt.
  2. Ensure your key is in C:\Users\your_username\.ssh\.
  3. Type: ssh username@hostname

Using PuTTY:

  1. Download PuTTY.
  2. Load your private key in the configuration.
  3. Enter your login information in the Host Name box and click Open.

VS Code allows you to edit files and run terminal commands directly on the HPC clusters.

  1. Download and install VS Code.
  2. Go to the Extensions view (click the square icon on the left sidebar).

  3. Search for and install the "Remote - SSH" extension by Microsoft (as shown above).

    VS Code Remote SSH Extension

  4. Click the green "><" icon in the bottom-left corner of the window.

  5. Select "Connect to Host...".
  6. Enter username@front01.hpcf.cyi.ac.cy (for Aphroditi)
  7. VS Code will connect, and you can open folders on the cluster as if they were local.

Option 3: Legacy/Alternative: PuTTY (Windows)

If you are unable to use OpenSSH or VS Code, you can use PuTTY.

  1. Download PuTTY.
  2. Run the executable (putty.exe).

  3. Browse for and select your private key file.

    Private Key selection

  4. Enter login information in the Host Name box (e.g. username@hostname) and click Open.

    Login info

Simplifying SSH with a Config File

For a smoother experience in both your terminal and VS Code, you can create an SSH configuration file on your local machine (~/.ssh/config on Linux/Mac, or C:\Users\your_username\.ssh\config on Windows).

Add the following to your config file:

# Global settings for HPC connections
ServerAliveInterval 30
ForwardAgent yes
IdentityFile ~/.ssh/id_rsa

Host aphroditi
  HostName front01.hpcf.cyi.ac.cy
  User your_username

Benefits of this setup:

  • Keep connections alive: ServerAliveInterval 30 prevents your connection from dropping due to inactivity.
  • Agent Forwarding: ForwardAgent yes allows you to use your local SSH keys on the login node.
  • Shortcuts: You can now connect to Aphroditi by simply running ssh aphroditi in your terminal, or by typing aphroditi in the VS Code "Connect to Host" box.
Managing SSH Config in VS Code

You can also manage this file directly inside VS Code:

  1. Click the green "><" icon in the bottom-left corner.
  2. Select "Configure SSH Host...".
  3. Select your ~/.ssh/config file from the list.
  4. Add the host entry above directly in the editor and save the file.