---
title: WTF is Linux
author: Rémi Nicole <remi.nicole@smile.fr>
date: 2020-09-22
slide-level: 2
aspectratio: 169

theme: metropolis
colortheme: owl
beameroption: "show notes on second screen=right"

toc: true
highlightstyle: breezedark
lang: en-US

bibliography: ../bibliography.bib
---

# Before we get started

## Requirements for the practical works

- A GNU/Linux machine
- An SD card reader
- A partner (if you want to)

## The website

- In here: <https://git.esiee.fr/nicolere/wtf-is-linux-website>
- Please contribute! <https://git-send-email.io/>
- Learn Git: <https://git-scm.com/book/en/v2>


::: notes

- If you have already used Git before, try to use the send-email approach
- If not, you can use the pull request method

:::

## Where were we?

::: notes

- Some history of computer science
- Downloaded, configured and build a kernel
- Tried to boot a Linux system, without success

:::

# The file system

## Purpose

- Organize ones and zeroes into files and directories
- It is therefore a "format"
- We can ask the kernel to represent the files and directories somewhere

::: notes

- Storage devices (HDDs, SSDs) just store ones and zeroes
- Representing the files is what is called "mounting"

:::

## Storage devices

- HDDs, SSDs, Flash Memory, everything is different
- We don't care about their differences
- Thank you device drivers


## Well-known file systems

- FAT32
- ext4
- NTFS

::: notes

- FAT32 works everywhere but
	- Fragmentation
	- no files bigger than 4 GB
	- no advanced features (FAT is quite old)
- ext4 is the de facto Linux file system
- NTFS is the standard Windows file system

:::


## Anatomy of a file system

- Need to store the content of files
- Need to store metadata
	- File names
	- File permissions
	- Where the content is
	- etc.

---

![FAT32 format [@mdpi:fat32]](../res/fat32.jpg){ width=70% }

---

![FAT32 table [@wikimedia:fat32_table]](../res/Fat32_structure.png){ height=70% }

## Partitions

- We need a way to store **several** file systems in a single hard drive
- This is quite similar to file systems
	- But we store partitions instead of files
- We call the format a "partitioning scheme"

::: notes

- Similar in that:
	- This is a format
	- We need metadata
	- And we need space for the partitions

:::

## Well-known partitioning scheme

- MBR
- GPT

## Anatomy of a partitioning scheme

![GPT format [@wikimedia:gpt]](../res/GUID-Partition-Table-Scheme.png){ height=80% }

## Block devices

- We need a way for the kernel to present us devices
- You can't directly present files
	- We may not have a file system in a partition
	- The kernel doesn't automatically where to "mount" the files


::: notes

- Philosophy of "everything is a file"
- Look at `/dev`
- `/dev/sda` is the first SCSI disk
- `/dev/sda1` is the first partition in the first SCSI disk
- Theses special files behave a lot like normal files

:::

## Mounting

- To the terminal!


::: notes

- Also talk about mount options

:::

## Special file system

- Common examples: `tmpfs`, `devtmpfs`, `sysfs` & `proc`

# Init

## Purpose

- We need a process launched by the kernel
- A process can launch other processes
- So let's make it 1

## Busybox


# References