Linux basics

What is WSL?

These notes are adapted from https://learn.microsoft.com/en-us/windows/wsl/about and https://learn.microsoft.com/en-us/virtualization/windowscontainers/about/containers-vs-vm

Windows Subsystem for Linux (WSL) is a feature of Windows that allows you to run a Linux environment on your Windows machine, without the need for a separate virtual machine or dual booting.

The following sections compare/contrast containers and VMs.

Container architecture

A container is an isolated, lightweight silo for running an application on the host operating system. Containers build on top of the host operating system’s kernel (which can be thought of as the buried plumbing of the operating system), and contain only apps and some lightweight operating system APIs and services that run in user mode, as shown in this diagram.

Virtual machine architecture

In contrast to containers, VMs run a complete operating system–including its own kernel–as shown in this diagram.

Linux Filesystem Hierarchy Standard (FHS)

These notes are adapted from https://en.wikipedia.org/wiki/Filesystem_Hierarchy_Standard

Raspberry Pi OS and Debian

The Raspberry Pi OS (previously called Raspbian OS) used in the reTerminal is a variation of the Debian OS, with optimizations for the Raspberry Pi hardware.

Debian OS is one of the most commonly used Linux distributions, especially as the “base” for derivative distributions. There are over 100 derivatives of Debian, many of which are themselves very popular distributions. These include:

• Desktop distributions like Ubuntu, Linux Mint, elementaryOS;

• Special-purpose distributions Kali Linux and Backbox (penetration testing)

• Server/Hypervisor distributions like Proxmox, Ubuntu server,

• Many others, you can find a more complete list here

Debian-derived distributions share the following:

• the .deb package format

• the dpkg package manager and its frontend apt

For that reason, many of the commands and configuration for Raspberry Pi OS can be taken directly from Debian’s documentation.

Apt: Debian Package Manger

The command apt is the default package manager of Debian.

A package manager is a software tool responsible for automating the installation, removal, configuration and removal of computer programs.

Managing packages could technically be done manually, however, it is very time consuming and error prone: tracking package dependencies and compatibility with the current system.

Common apt commands

There are many apt commands you will find yourself using all the time on a Debian-based OS like Raspberry Pi. It’s worth knowing in a bit more detail how they work.

Note: Online, you will often see apt-get used instead of apt. apt is a newer package manager API meant to replace the older API apt-get. However, they both do more or less the same things the same ways, and apt is a backwards compatible replacement for apt-get in all cases. See Debian docs for details.

During Lab 1, you updated, upgraded and installed some packages in the Raspberry Pi OS using apt:

Command	Description
sudo apt update	Update list of available packages
sudo apt upgrade	Upgrade the system by installing/upgrading packages

apt:

the difference between update and upgrade {.striped .hover .column-body-outset-right}

Combined, these two commands update and upgrade all of the currently operating system packages on your system:

$ sudo apt update && sudo apt upgrade -y

There are a few other apt commands worth knowing.

Command	Description
apt list	list packages installed on your system based on package names.
apt search <query>	Returns all repository packages search in package descriptions
apt show <package>	show package details
apt install <package>	install packages
apt reinstall <package>	reinstall packages
apt remove <package>	remove packages

apt:

a variety of other commands I find myself using now and again {.striped .hover .column-body-outset-right}

You can see details about all of these commands and more by running apt --help. Note: documentation will often leave out sudo since the need to run sudo depends on the machine and the user.

In general, commands that read data (apt list, apt search, etc.) will generally not require sudo, since most folderst that apt will touch are universally readable.

apt commands that write data (apt install, etc.) to a folder not owned by the current user – which is most folders outside of /home/username, but particularly common package install locations like /usr, /bin, etc. – these commands will require sudo to gain the required write permission

Apt source repositories explained

This section has been adapted directly from the Debian documentation: see SourcesList

Apt downloads packages from one or more software repositories (sources) and installs them onto your computer.

A repository is generally a network server, such as the official DebianStable repository. Local directories or CD/DVD are also accepted.

The specific repositories (package sources) configured on your machine affect: - What software packages are available for download - What versions of packages are available - Who packages the software

Commonly used package sources

• DebianStable: official Debian repository for the current release

• StableProposedUpdates: official Debian repository for upcoming point releases (security and important bug fixes every ~2 months)

• StableUpdates: official Debian repository for changes that cannot wait for the next point release, packages are also added to StableProposedUpdates for inclusion in the next point release

• DebianSecurity: official Debian repository for frequent security updates

• DebianBackports: more recent versions of some packages, compatible with DebianStable.

• DebianUnstable: rolling development version containing the latest packages

• DebianExperimental: development version containing the experimental/alpha/beta/untested packages

Editing Software Sources

Being able to change the repositories used by your package management system is a powerful feature but this power comes with some responsibility.

Users are cautioned that it is possible to break your system (in a way that could be difficult or impossible to cleanly fix) by adding third-party repositories, or repositories for a Debian version that does not match your current version - these repository create a risk of conflicting package versions, creating what’s sometimes called a “Franken-Debian” system.

The whole concept behind a Debian stable release is that the Debian developers have picked a set of software and their versions that function nicely together. While this software is patched to fix security issues, the software is frequently not the latest version. It takes some experience to know how the repos may be changed without risk of breaking your system. Users of all levels are advised to change repos cautiously.

L1 Part 2: Bash Better   L2: Reterminal setup