3. Logging Into Falcon for the First Time

This guide will walk you through connecting to the Falcon supercomputer. We’ll cover SSH basics, configuring your connection, setting up your environment, and transferring files.

3.1. Prerequisites

Before you start, make sure you:

  • Have completed the registration steps in the System Access guide

  • Have VPN access to Cardiff University

  • Have turned on your VPN (seriously, this is required for every connection)

  • Have a terminal open on your local machine

3.2. Understanding SSH

SSH (Secure Shell) is a way to securely log into a remote computer over the internet. When you SSH into Falcon, you’re opening a secure connection to the supercomputer and getting a shell (command prompt) where you can type commands.

The basic SSH command looks like this:

ssh username@hostname

For Falcon, this would be:

ssh yourusername@falconlogin.cf.ac.uk

When you run this command:

  1. SSH asks for your password

  2. You type your password (it won’t show on screen—this is normal)

  3. You get a command prompt on the remote machine

  4. You can now type commands that run on Falcon instead of your local computer

3.3. Your First Login

  1. Make sure your VPN is on—check your system settings to confirm

  2. Open your terminal

  3. Type the SSH command:

    ssh yourusername@falconlogin.cf.ac.uk

  4. Press Enter

  5. When prompted, enter your Falcon password

  6. You should now see a prompt that looks something like [yourusername@falconlogin ~]$

Congratulations! You’re now logged into Falcon.

To log out, type:

exit

or press Ctrl+D

3.4. Simplifying Login with SSH Config

Typing the full hostname every time is tedious. SSH has a configuration file where you can define shortcuts. You can create a file at ~/.ssh/config that makes logging in much easier. If you aren’t familiar yet with how to create or edit files in the terminal, check out the Basics of Bash guide. In short, you can use a text editor like vi, nano, or vim to create the file:

vi ~/.ssh/confic

Once you have created a file here’s an example .ssh configuration for Falcon that you can paste into it:

Host falcon
  HostName falconlogin.cf.ac.uk
  User yourfacadeusername
  ServerAliveInterval 240

With this configuration in place, you can now simply type:

ssh falcon

and you’ll be connected to the same system.

The ServerAliveInterval 240 line tells SSH to send a signal every 240 seconds to keep your connection alive if you’re idle—useful for long-running sessions.

You can add multiple hosts to your ~/.ssh/config file for different systems you connect to. If you want to see more examples, check out Omar’s dotfiles repository.

3.5. Setting Up Your Environment with Dotfiles

When you log into a system, several startup files run to configure your environment. These typically include:

  • .bashrc - Bash configuration file

  • .bash_profile - Bash login configuration

These files can contain:

  • Exports: Setting environment variables (like PATH, PYTHONPATH, etc.)

  • Aliases: Shortcuts for common commands (e.g., alias ll='ls -lah')

  • Functions: Custom commands you can run

  • Module loads: Loading necessary software (modules on HPC systems)

These dotfiles allow us to predefine specific commands that will automatically be run whenever we log in to a remote server like Falcon. This can save us a lot of time! Rather than manually editing these files on the remote system, many developers maintain “dotfiles”—a repository of configuration files that can be cloned and installed on any system.

Omar maintains a dotfiles repository at:

https://github.com/omarnawaz/dotfiles

This repository contains configurations for:

  • Shell aliases and functions

  • Environment variable exports

  • Useful utilities for working on HPC systems

  • Development tool configurations

You can explore this repository to see useful patterns you might want to adopt. Some common dotfile elements include:

Aliases (shortcuts for commands):

alias ll='ls -lah'
alias gst='git status'
alias gco='git checkout'

Exports (environment variables):

export PYTHONPATH="/path/to/your/python:$PYTHONPATH"
export OMP_NUM_THREADS=4

Functions (custom commands):

function mkcd() {
  mkdir -p "$1" && cd "$1"
}

On Falcon, your startup files will be on the remote system. You can edit them directly on Falcon or clone your own dotfiles repository into your Falcon home directory and source them from your .bashrc file.

3.6. Transferring Files with SCP

Now that you can log in, you’ll probably want to transfer files between your local machine and Falcon. The scp command (Secure Copy) lets you do this.

Copying a file FROM your local machine TO Falcon:

scp /path/to/local/file falcon:/path/to/remote/destination

For example, to copy a script called analysis.py to your home directory on Falcon:

scp ./analysis.py falcon:~/

Copying a file FROM Falcon TO your local machine:

scp falcon:/path/to/remote/file /path/to/local/destination

For example, to copy results from Falcon to your local machine:

scp falcon:~/results/output.txt ./

Copying a whole directory:

Add the -r flag (recursive) to copy directories:

scp -r falcon:~/mydata ./mydata_backup

A few tips:

  • ~ on the remote system refers to your home directory on Falcon

  • ./ on the local system refers to the current directory on your local machine

  • You can use wildcards: scp falcon:~/data/*.txt ./ copies all .txt files

  • If you set up an SSH config entry for falcon (as shown above), SCP will automatically use those settings

3.7. Workflow Example

Here’s an example workflow:

  1. Write code locally in your favorite editor

  2. Copy it to Falcon using SCP:

    scp ./myanalysis.py falcon:~/projects/

  3. Log into Falcon:

    ssh falcon

  4. Run your code on Falcon’s compute resources

  5. Copy results back to your local machine:

    scp falcon:~/projects/results.txt ./

  6. Log out:

    exit

Later on we will walk through how to directly use an IDE (VSCODE) to develop on a remote.

3.8. Troubleshooting

“Connection refused” or “Network unreachable”: - Check that your VPN is on - Verify you can access other Cardiff resources

“Permission denied (publickey,password)”: - Check that your username is correct in your SSH config - Verify your Falcon password hasn’t expired - Make sure you’re using your Falcon username, not your Cardiff username

“Connection closed by remote host”: - Your connection may have timed out - Simply reconnect with ssh falcon

SCP says “No such file or directory”: - Double-check your file paths - Remember that ~ refers to your home directory on the remote system - Use pwd to check your current location

3.9. Need Help?

If you run into issues: