(Almost Painless) SSH Setup Guide

Prepared by Qingqing Ni

1. Student Guide: Set Up an SSH Key

Complete the following steps inside your Ubuntu virtual machine.

Step 1 — Generate an SSH Key

Open a terminal and run:

ssh-keygen -t ed25519 -C "AY<YYYY>S<S>"

Replace <YYYY> with the current academic year and <S> with the current semester.

For example, for Academic Year 2026/2027, Semester 1:

ssh-keygen -t ed25519 -C "AY2627S1"

The comment allows the teaching team to identify and clear student SSH keys from a particular semester.

You will see a prompt similar to:

Enter file in which to save the key (/home/username/.ssh/id_ed25519):

Press Enter to use the default location.

You will then be asked for a passphrase. For the lab setup, you may press Enter to leave it empty.

This creates two files:

~/.ssh/id_ed25519
~/.ssh/id_ed25519.pub

• id_ed25519 is your private key. Do not share it.
• id_ed25519.pub is your public key. This is the key that will be added to the Raspberry Pi.

Step 2 — Copy Your Public Key to the Raspberry Pi

Run:

ssh-copy-id balance@balanceX.local

where X is the number assigned to your Raspberry Pi.

Alternatively, you may connect using its IP address:

ssh-copy-id balance@192.168.1.xx

Enter the password 030609 when prompted.

You should only need to enter this password once.

Step 3 — Test the Connection

Run:

ssh balance@balanceX.local

or:

ssh balance@192.168.1.xx

You should now be able to log in without entering the Raspberry Pi password.

2. SSH Shortcuts

On your VM, open:

nano ~/.ssh/config

Add:

Host <nickname>
    HostName balanceX.local
    User balance

Host <nickname>-ros
    HostName balanceX.local
    User balance
    RequestTTY force
    RemoteCommand bash -lc 'docker start ros2_humble >/dev/null 2>&1 || true; docker exec -it -w /home/ros2_ws ros2_humble bash'

Replace <nickname> with your preferred shortcut and X with the number assigned to your Raspberry Pi. For this manual, we will use car as the shortcut.

Set the correct permission for the SSH configuration file:

chmod 600 ~/.ssh/config

You can now use:

ssh car

to open a normal SSH session on the Raspberry Pi.

Or use:

ssh car-ros

to enter the ROS 2 Docker container directly at:

/home/ros2_ws

The car-ros shortcut will start the ros2_humble container automatically if it is not already running.

3. Clearing Student SSH Keys

All SSH public keys added to the balance account are stored in:

/home/balance/.ssh/authorized_keys

Each public key normally occupies one line. Student keys generated using the instructions above will end with a comment such as:

AY2627S1

Check Existing Student Keys

Before removing anything, you can list the student keys for a particular semester using:

grep "AY<YYYY>S<S>" /home/balance/.ssh/authorized_keys

For example:

grep "AY2627S1" /home/balance/.ssh/authorized_keys

This only displays matching keys and does not modify the file.

Remove Student Keys for the Semester

To remove all student keys for a particular semester, run:

sed -i '/AY<YYYY>S<S>/d' /home/balance/.ssh/authorized_keys

For example, to remove all keys labelled AY2627S1:

sed -i '/AY2627S1/d' /home/balance/.ssh/authorized_keys

This removes only lines containing:

AY2627S1

Other SSH keys in the file are left unchanged.

You can verify that the student keys have been removed using:

grep "AY<YYYY>S<S>" /home/balance/.ssh/authorized_keys

If there is no output, no matching student keys remain.

You can also inspect all remaining authorised keys using:

cat /home/balance/.ssh/authorized_keys

sudo chown balance:balance /home/balance/.ssh/authorized_keys
sudo chmod 700 /home/balance/.ssh
sudo chmod 600 /home/balance/.ssh/authorized_keys