path: root/2020-09-08.md

---
title: WTF is Linux
author: Rémi Nicole <remi.nicole@smile.fr>
date: 2020-09-08
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
---

# The Project

## Building a Linux system manually

- This is the Course (You are Here)
- Using just normal commands

::: notes

Hello

:::

## Building a Linux system automatically

- Practical Work
- Buildroot


## Why

- Linux is everywhere in embedded software
- Linux is everywhere in the server space


# History

## 17th century to 1970s

:::: columns

::: column
![Human computer at NACA [@wikimedia:human_computer]](../res/Human Computer.jpg){ height=80% }
:::
::: column
![Katherine Johnson working as a Human computer at NASA [@wikimedia:katherine_johnson_human_computer]](../res/Katherine Johnson at NASA.jpg){ height=80% }
:::

::::

::: notes

- NACA: National Advisory Committee for Aeronautics
- "Computer" referred to the person that did mathematical computation
  / verification
- Verify trajectories for putting men into Earth orbit
- Katherine Johnson on the right
- You can watch the movie "Hidden Figures"

:::

## 1930s-1940s

![Bletchley Park Bombe [@wikimedia:bletchley_park_bombe]](../res/Bletchley Park Bombe.jpg){ width=45% height=80% }

::: notes

- You can watch the movie "The Imitation Game"

:::

## 1950s

::: columns

:::: column
![IBM 704 Mainframe [@wikimedia:ibm_704_mainframe]](../res/IBM 704 mainframe.jpg){ height=80% }
::::

:::: column
![IBM 709 Mainframe [@ibm:ibm_709_mainframe]](../res/IBM 709 mainframe.jpg){ height=80% }
::::

:::

::: notes

- There are lights and switches
- Back in the day, there were used to inspect and modify memory / registries or
  see the executed instructions
- Already two influential programming languages existed:
	- FORTRAN (formula translation)
	- Lisp
- We can see:
	- The Operator's Console
	- The Central Processing Unit (CPU)
	- The Punch card reader
	- The Magnetic Tape Unit (for long term storage)
- Very few "professional programmers"

:::

## 1950s---The line printer

![IBM 716 Line Printer [@ibm:ibm_716_line_printer]](../res/IBM 716 line printer.jpg){ height=80% }

::: notes

- Really shaped the terminal as we know today

:::

## 1969

:::: columns

::: column

Things were pricey:

- Disk 180MB -> 32,000$
- Commercial compiler -> 100,000$
:::

::: column
![Boot [@needpix:boot]](../res/boot.png){ height=80% }
:::

::::

::: notes

- You could buy a very nice house for 32,000$

:::


## 1970s---UNIX {.allowframebreaks}

![Ken Thompson (sitting) and Dennis Ritchie working together at a PDP-11 [@wikimedia:ken_thompson_dennis_ritchie]](../res/Ken Thompson and Dennis Ritchie at PDP-11.jpg){ height=67% }

::: notes

- He is actually coding using the teletypewriter

:::

\framebreak

- Smaller, for one person[@fosdem:fifty_years_of_unix]
- They actually used their own operating system
- Invented C a bit later (1972)
- Definitely not "free", barely "open":
	160,000 $ per CPU

Berkeley university made BSD out of it (was called Berkeley UNIX)

::: notes

- Targeted at big companies

:::

\framebreak

- Same OS, different computers
- Compiler took care of the difference in architecture.

::: notes

- Big advantages when compared to other solutions
- This made UNIX popular, and by extension the C programming language too

:::

\framebreak

Invented over the years by contributions:

- shell (command interpreter)
- pipes and filters in shell commands
- Network file system (NFS)
- Client/Server Windowing System
- etc.

## 1980s---GNU (Richard Stallman)

1983:
: GNU project annouced

1985:
: Created the Free Software Foundation (helps funding)

1989:
: Created GNU General Public License (GPL)

Created:

- Text editor (Emacs)
- Compiler suite
- Lots of utilities

People could use these tools in different operating system

::: notes

- Frustrated by his printer
- Internet was widely used in academia

:::

## 1990s---POSIX

- Lots of different "UNIX-like" operating system existed
- There was no proper definition of what "UNIX-like" meant

## 1991--The Linux kernel (Linus Torvalds)

- Just for fun
- Needed a license

::: notes

- Got an Intel i386 processor for Christmas
- Wasn't happy with the OS (he wanted page-based memory)
- Started writing a kernel, just for fun
- He was 21 years old
- The current situation made it possible:
	- Powerful "cheap" computers
	- "Faster" internet where you could find information about operating system
	  and hardware architecture

:::

## 1994--Windows NT

Bleurgh

::: notes

- Made the "personal computer" popular
- Based on a shitty technology from IBM called DOS

:::

## 1990s--Linux gaining popularity

- Free
- More choice for architecture
- Real TCP/IP stack


::: notes

- Wow, you want to connect to the internet?!

:::

# Command-line primer

## Most commands

```console
Copies the file "file_1.txt" into "file_2.txt"
user@host:~$ cp    file_1.txt    file_2.txt
             ^^    ^^^^^^^^^^    ^^^^^^^^^^
             |         |             |
             |         '-------------'- arguments
             |
             '---------------------- command name (verb)
```

## The prompt

```console
 ,------ username you are logged in as
 |
 |        ,---- directory you are in,
 |        |     '~' means your user directory
vvvv      v
user@host:~$
     ^^^^  ^
      |    |
      |    '--- '$' if you are a normal user,
      |         '#' if you are the root user
      |
      '--- name of the machine you are on
```

## POSIX & GNU conventions

```console
                       ,-------------- long option / flag
                       |
                       |           ,-- short option / flag
                       |           |
             vvvvvvvvvvvvvvvvvvvvv vv
$ git commit --message="My commit" -S src/main.cpp
  ^^^ ^^^^^^                          ^^^^^^^^^^^^
   |    |                               |
   |    '----------------------------- subcommand or argument
   |
   '---------------------------------- command name
```

# The kernel

## Role

Well, it depends on the kernel

::: notes

Some kernel are very small, some

:::

---

![Monolithic kernel vs Microkernel](../res/OS-structure.pdf){ height=80% }

## The Linux kernel

- Monolithic kernel:
  - Drivers are in the kernel
  - File-systems (ext4, fat32, etc.) are in the kernel
  - Lots of other things


## Communicating with the Linux kernel

- System calls

::: notes

- They look like functions in C code, but that's a lie, it's a hardware feature
  using interrupts

- That's it
- Kinda
- We can't have one system call for everything
  - Different system calls for different types of hardware

:::

. . .

- Everything is a file

::: notes

- We have special files and special file-systems
  - They look like files, but that's a lie
  - Reading / Writing to it does *not* read / write to storage
  - Instead it's like calling a function of the kernel
- Example with `/proc/cpuinfo`

:::

## Compiling a kernel

Let's do it

## Linux boot process


```
Boot loader
    |
    | loads
    v
Linux kernel
    |
    | launches
    v
init (first user process)
    |
    | does whatever it wants
    v
  ?????
```

::: notes

- We're not going to talk about the boot loader
- Example with `htop`

:::

# References