How do I connect to a HPC Cluster?

How do I connect to a HPC Cluster?#

Learning Objectives#

  • Connect to the ISCA HPC system using university credentials

  • Create an SSH config file for easier access via the command line

  • Verify the installation of the SSH application on various operating systems

  • Understand the steps involved in logging into an HPC cluster for the first time

  • Utilize graphical interfaces like Putty for connecting to HPC systems

Via the Command Line#

Checking#

The most common way to connect to a remove HPC server is via a command line shell program ssh. This application uses the Secure SHell protocol (or SSH) to open an encrypted network connection between two machines, allowing you to send & receive text and data without having to worry about prying eyes. It should be available in all terminal apps (Windows, Linux, & Mac), but to doublecheck type ssh into your terminal of choice and press enter. If it is installed properly, you should get output like that below.

you@laptop:~$ ssh

usage: ssh [-46AaCfGgKkMNnqsTtVvXxYy] [-B bind_interface]
           [-b bind_address] [-c cipher_spec] [-D [bind_address:]port]
           [-E log_file] [-e escape_char] [-F configfile] [-I pkcs11]
           [-i identity_file] [-J [user@]host[:port]] [-L address]
           [-l login_name] [-m mac_spec] [-O ctl_cmd] [-o option] [-p port]
           [-Q query_option] [-R address] [-S ctl_path] [-W host:port]
           [-w local_tun[:remote_tun]] destination [command [argument ...]]

If you do not get this output, please let the instructor know. But don’t worry, there are other means of connecting to the system and well will cover those in a moment.

Logging In#

Assuming you were given access to the system by an administrator, you should be able to login with your standard university credentials. The syntax for logging into a machine with ssh is

you@laptop:~$ ssh username@hostname

where username is your standard login and the hostname is address of the server you wish to log into. For this workshop the hostname will be login02.isca.ex.ac.uk. Don’t forget the @ symbol, like you would see in an email address. You will then be prompted for your university password.

First Time Warning#

An important security warning will occur whenever you attempt to log into another machine for the first time.

The authenticity of host 'login02.isca.ex.ac.uk (144.173.114.23)' can not be established.
ED25519 key fingerprint is SHA256:rPqlD8myIfJUQBINKPYCp47oIQm3sGVMUPSAWT26E/M.
ECDSA key fingerprint is SHA256:ah29tkixxl7NW/zdJM6TSbASY3UyLsKZEKUMMZSD3X0.
This key is not known by any other names
Are you sure you want to continue connecting (yes/no/[fingerprint])?

Make sure that the IP address (i.e. 144.173.114.23) and the appropriate key fingerprint that you get match the information found above. Any subsequent time you log into that same server, you should not see this message, as this server’s fingerprint is saved in a list of known_hosts. If you do get this message while connecting to a server you have logged into previously, please contact a system administrator immediately.

Config File#

Remembering the long hostnames can be a pain. We can create a config file that allows us to use shorter and more memorable ones for machines we use regularly using an ssh config file. For those using a Unix terminal, the two commands below will create a file with access restricted to just the current user.

touch ~/.ssh/config
chmod 600 ~/.ssh/config

Open up that file in your preferred text editor and copy the following example into it. Remember to swap your specific username for the placeholder.

# Configuration file for simplifying SSH logins
Host login.isca
    User your_username
    Hostname login02.isca.ex.ac.uk

Now you can log in with a far shorter and easier to remember command. But you still will be prompted for your password.

you@laptop:~$ ssh login.isca

Graphical Interfaces#

An alternative means of connecting to a remote host server is via an application like the Putty SSH Client. It provides nice app-based way to save host connection configs so one need not input them again each time. Like the command line option, if you haven’t logged in before, it will raise a warning message.

You will be prompted in a new terminal session for your username and password.