Connecting to the remote HPC system

Overview

Teaching: 20 min
Exercises: 10 min

Questions

• How do I open a terminal?

• How do I connect to a remote computer?

Objectives

• Connect to a remote HPC system.

Opening a Terminal

Connecting to an HPC system is most often done through a tool known as “SSH” (Secure SHell) and usually SSH is run through a terminal. So, to begin using an HPC system we need to begin by opening a terminal. Different operating systems have different terminals, none of which are exactly the same in terms of their features and abilities while working on the operating system. When connected to the remote system the experience between terminals will be identical as each will faithfully present the same experience of using that system.

Here is the process for opening a terminal in each operating system.

Linux

There are many different versions (aka “flavours”) of Linux and how to open a terminal window can change between flavours. Fortunately most Linux users already know how to open a terminal window since it is a common part of the workflow for Linux users. If this is something that you do not know how to do then a quick search on the Internet for “how to open a terminal window in” with your particular Linux flavour appended to the end should quickly give you the directions you need.

A very popular version of Linux is Ubuntu. There are many ways to open a terminal window in Ubuntu but a very fast way is to use the terminal shortcut key sequence: Ctrl+Alt+T.

Mac

Macs have had a terminal built in since the first version of OS X (now macOS) as it is built on a UNIX-like operating system, leveraging many parts from BSD (Berkeley Systems Designs). The terminal can be quickly opened through the use of the Searchlight tool. Hold down the command key and press the spacebar. In the search bar that shows up type “terminal”, choose the terminal app from the list of results (it will look like a tiny, black computer screen) and you will be presented with a terminal window. Alternatively, you can find Terminal under “Utilities” in the Applications menu.

Windows

If you are using Windows, you should have installed Git Bash as part of the setup for this course which includes an SSH client you can use in the same way as for Linux and Mac. Open the Git Bash program to get terminal access.

Logging onto the system

With all of this in mind, let’s connect to a remote HPC system. In this workshop, we will connect to Cirrus — an HPC system located at the EPCC, The University of Edinburgh. Although it’s unlikely that every system will be exactly like Cirrus, it’s a very good example of what you can expect from an HPC installation. To connect to our example computer, we will use SSH.

SSH allows us to connect to UNIX computers remotely, and use them as if they were our own. The general syntax of the connection command follows the format ssh yourUsername@some.computer.address Let’s attempt to connect to the HPC system now:

ssh yourUsername@login.cirrus.ac.uk

The authenticity of host 'login.cirrus.ac.uk (129.215.175.28)' can't be established.
ECDSA key fingerprint is SHA256:JRj286Pkqh6aeO5zx1QUkS8un5fpcapmezusceSGhok.
ECDSA key fingerprint is MD5:99:59:db:b1:3f:18:d0:2c:49:4e:c2:74:86:ac:f7:c6.
Are you sure you want to continue connecting (yes/no)?  # type "yes"!
Warning: Permanently added the ECDSA host key for IP address '129.215.175.28' to the list of known hosts.
yourUsername@login.cirrus.ac.uk's password:  # no text appears as you enter your password
Last login: Wed Nov 28 08:46:30 2018 from cpc102380-sgyl38-2-0-cust601.18-2.cable.virginm.net

================================================================================

Cirrus HPC Service

--------------------------------------------------------------------------------
This is a private computing facility. Access to this system is limited to those
who have been granted access by the operating service provider on behalf of the
issuing authority and use is restricted to the purposes for which access was
granted. All access and usage are governed by the terms and conditions of access
agreed to by all registered users and are thus subject to the provisions of the
Computer Misuse Act, 1990 under which unauthorised use is a criminal offence.
--------------------------------------------------------------------------------

For help please contact the Cirrus helpdesk at: 
support@cirrus.ac.uk

================================================================================

If you’ve connected successfully, you should see a prompt like the one below. This prompt is informative, and lets you grasp certain information at a glance. (If you don’t understand what these things are, don’t worry! We will cover things in depth as we explore the system further.)

[yourUsername@cirrus-login0 ~]$ 

Telling the Difference between the Local Terminal and the Remote Terminal

You may have noticed that the prompt changed when you logged into the remote system using the terminal (if you logged in using PuTTY this will not apply because it does not offer a local terminal). This change is important because it makes it clear on which system the commands you type will be run when you pass them into the terminal. This change is also a small complication that we will need to navigate throughout the workshop. Exactly what is reported before the $ in the terminal when it is connected to the local system and the remote system will typically be different for every user. We still need to indicate which system we are entering commands on though so we will adopt the following convention:

• [local]$ when the command is to be entered on a terminal connected to your local computer
• [yourUsername@cirrus-login0 ~]$ when the command is to be entered on a terminal connected to the remote system
• $ when it really doesn’t matter which system the terminal is connected to.

Being certain which system your terminal is connected to

If you ever need to be certain which system a terminal you are using is connected to then use the following command: $ hostname.

Keep two terminal windows open

It is strongly recommended that you have two terminals open, one connected to the local system and one connected to the remote system, that you can switch back and forth between. If you only use one terminal window then you will need to reconnect to the remote system using one of the methods above when you see a change from [local]$ to [yourUsername@cirrus-login0 ~]$ and disconnect when you see the reverse.

Key Points

• To connect to a remote HPC system using SSH: ssh yourUsername@remote.computer.address