LX: Linux and Networking#

What you will need

What you will get

  • An understanding of the basics of Linux and networking, including the command line, file system, and network configuration.

This Learning Experience introduces Linux and networking concepts in the context of Duckietown. You will learn about the command line, file system, and network configuration.

Linux and Networking

Fig. 90 “The hardest part of robotics is networking.”#

Intended Learning Outcomes

After completing this learning experience, learners will be able to:

  • Distinguish the Linux kernel, distributions, user space, and central processing unit (CPU) architecture before navigating a Linux filesystem. Create and safely manage files, use wildcards and searches, interpret command results, understand standard streams, redirection, pipes, variables, permissions, processes, and trusted shell scripts, and write and verify small Python and shell programs that read from and write to standard streams.

  • Explain how Media Access Control (MAC) addresses, Internet Protocol (IP) addresses, subnets, gateways, Dynamic Host Configuration Protocol (DHCP), Network Address Translation (NAT), firewalls, Domain Name System (DNS), multicast Domain Name System (mDNS), ports, and network quality support Duckiedrone connectivity. Use authorized, targeted ip, getent, ping, nc, ss, curl, and dts fleet discover checks to investigate a connection.

  • Distinguish a base-station shell, a physical Duckiedrone Secure Shell (SSH) shell, a virtual Duckiedrone shell, and a service shell. With explicit authorization, access one Duckiedrone and inspect its filesystem, processes, and running services without changing device state.

Available repositories

Warning

If you are using a Duckietown Workspace, the WebGL (browser) versions of the Duckietown Viewer and Duckiematrix can be run inside or outside the Duckietown Workspace. If dts is installed on the host machine, commands that launch native Duckietown Viewer apps or the Duckiematrix Renderer, such as dts matrix run, can also be run in either location. When one of these commands is run inside the Duckietown Workspace, it is automatically delegated to the host machine, where it launches the native UI. The --standalone flag starts the Duckiematrix Engine in the environment where the command is run.

About these learning activities#

Note

This learning experience introduces a number of Linux concepts and tools that can be run on any Ubuntu system. A native installation of a supported Ubuntu version, or a Duckietown Workspace, is recommended. Examples are worked out on physical and virtual Duckiedrones.

Notebooks#

Each notebook includes hands-on learning activities and a checkpoint to self-assess understanding. Work through the notebooks in order, since each one builds on the previous ones.

Notebook

Topics

1

Linux kernel, user space, CPU architecture, and distributions

2

Terminal, shell, current directory, and paths

3

Variables, quoting, PATH, and environment values

4

Creating, inspecting, copying, renaming, and removing files

5

Filename conventions, wildcards, find, and grep

6

Command help, error recovery, and exit status

7

Standard input (stdin), standard output (stdout), standard error (stderr), and redirection

8

Pipes and text processing

9

Shell scripts, execution, and sourcing

10

Users, ownership, and permissions

11

Processes, monitoring, and job control

12

Shell exercises and output verification

13

Physical Duckiedrone access through SSH

14

Virtual Duckiedrone connections

15

Duckiedrone filesystem inspection

16

Duckiedrone process inspection

17

Network addresses, subnets, routing, gateways, and IPv6

18

Network protocols, ports, packet layers, and connection quality

19

Localhost and service binding

20

DHCP, private addresses, NAT, firewalls, and access policy

21

DNS, mDNS, URLs, and service discovery

22

Network diagnostics, local TCP listeners, and Duckiedrone connection testing

Forking the Repository#

The recommended way to use the repository of an LX is to make a fork, and then clone that fork. Forking can be done through the GitHub web interface, and creates a personal copy that can still be synchronized with the upstream Duckietown code.

Cloning the repository directly also works, at the cost of not being able to push personal changes.

  1. Create a fork: navigate to the lx-dd-linux-and-networking repository.

    Find and press the “Fork” button on the top right:

    how to fork a Duckietown LX repository

    Fig. 91 Fork the LX to be able to make local changes while still being able to receive updates.#

    This creates a new repository at <your_github_username>/lx-dd-linux-and-networking.

  2. Clone the fork: clone the fork on the computer, replacing the GitHub username in the command below, and navigate to the new folder:

     git clone [email protected]:<your_github_username>/lx-dd-linux-and-networking
 cd lx-dd-linux-and-networking

  3. Configure upstream repo: configure the Duckietown version of this repository as the upstream repository to synchronize with the fork.

    List the current remote repository for the fork,

     git remote -v

    Specify a new remote upstream repository,

     git remote add upstream https://github.com/duckietown/lx-dd-linux-and-networking

    Confirm that the new upstream repository was added to the list,

     git remote -v

    Work can now be pushed to the personal repository using the standard GitHub workflow, and the beginning of every exercise prompts a pull from the upstream repository, updating the exercises to the latest version.

Keeping the System Up To Date#

  • 💻 These instructions are for ente learning experiences. Ensure that the Duckietown Shell is set to an ente profile (and not a daffy one). The current profile is shown by:

    dts profile list

    To switch to an ente profile, follow Initial setup.

  • 💻 Pull from the upstream remote to synchronize the fork with the upstream repo:

    git pull upstream ente

  • 💻 Make sure the Duckietown Shell is updated to the latest version:

    pipx upgrade duckietown-shell

  • 💻 Update the shell commands:

    dts update

  • 💻 Update the computer and the Duckiedrone: follow Preparing the software stack.

SSL Certificate Setup#

Note

This procedure is only needed the first time an LX is run on a new computer.

Duckietown uses SSL certificates and TLS encryption to guarantee the highest standard of safety and privacy. Set up a local SSL certificate needed to run the LX editor inside the browser:

sudo apt install libnss3-tools
dts setup mkcert

Note

If a Duckietown Workspace is in use, install mkcert on the host system by following the workspace setup instructions instead of running these commands inside the dev container.

Launching the Code Editor#

Important

All dts code commands must be executed inside the root directory of the learning experience.

From inside the directory of the learning experience, open the code editor by running:

dts code editor

Wait for a URL to appear on the terminal, then click on it or copy-paste it in the address bar of the browser to access the code editor. The first thing shown in the code editor is a version of these instructions. The indications shown in the code editor take precedence over this page.

Walkthrough of Notebooks#

Inside the code editor, use the navigator sidebar on the left-hand side to navigate to the notebooks directory and open the first notebook.

Follow the instructions on the notebook and work through them in sequence.

Testing with the Duckiematrix#

This learning experience explores the fundamentals of bash programming and networking. The Duckiematrix is not needed to complete this learning experience. The notebooks on virtual Duckiedrone connections only need a virtual Duckiedrone, created and started as follows.

1. Creating and starting a virtual Duckiedrone#

If this has not been done already (e.g., for a different LX), create a virtual Duckiedrone with the command:

dts duckiebot virtual create --type duckiedrone --configuration DD24 [VDRONE]

where [VDRONE] is the hostname. It can be any name, subject to the same naming constraints of physical Duckiedrones.

When the command runs, DTS prompts for a password for the virtual Duckiedrone’s duckie account, and asks to confirm it. The password must contain at least eight characters and cannot contain colons or line breaks. The typed characters are not displayed.

Then start the virtual robot with the command:

dts duckiebot virtual start [VDRONE]

The virtual Duckiedrone appears with status Booting and finally Ready in the output of dts fleet discover:

         | Hardware |    Type     | Model |  Status  |    Address
-------- | -------- | ----------- | ----- | -------- | --------------
[VDRONE] |  virtual | duckiedrone | DD24  |  Ready   | [VDRONE].local

Note

The Duckiedrone software stack runs on ROS 2. When running ROS 2 commands against a virtual or physical Duckiedrone from the computer, the ROS_DOMAIN_ID must match the one used by the robot.

Troubleshooting#

For more detailed instructions, refer to General Procedure for Running Learning Experiences. For help troubleshooting common problems, refer to its troubleshooting section.