Kernel Development Learning Pipeline

Linux System Basics

A time saver for vim users

Append these two lines to your ~/.vimrc to auto-highlight whitespace errors in your editor:

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Linux crash course and minimal distro

• We started with the Linux Crash Course slide deck.
• First, we gave the general what, where, why, and who of Linux
  • Free and open source operating system kernel and ecosystem
  • Running on many systems large and small, fast and slow, distributed and centralized
  • Many pre-packaged combinations of system components capable of running user applications are available
  • We call one of these a Linux distribution, or distro for short.
  • Some examples are Fedora, Ubuntu, Arch Linux, RHEL, Puppy, and TAILS
• Having motivated our discussion of system components, we proceeded to discuss each one briefly
  • We quickly went through the bootloader, kernel, C standard library, shared libraries, storage configuration, and filesystem hierarchy layout
  • As we were about to proceed to the demo, we didn’t go into great detail
  • Take note of the availability of manpages: run man man and read through the description.
• After finishing the slide deck, we build a minimal Linux distribution live
  • Using a ruthlessly minimal .config file, we built the kernel in noticeably less time than it took to clone, even with the --depth=1 option. Barely minutes.
  • Then, we tested this kernel with qemu-system, generating a kernel panic as expected
  • This is because the kernel attempts to start an initial userspace process and no such thing exists on the system
  • On many Linux systems, systemd is this first “init” process, and it is given PID 1
  • We then created a root filesystem and a “hello world” init process
  • This native assembly simply prints hello world
  • Take note that the entry point is _start and not main
  • Normally this is hidden as libc does various init things between _start and the user-defined main
  • We used strace to see how our little app talks to the kernel
  • In order to pass the app binary into the kernel, we use cpio to create an archive usable as an initial ram disk for our system, which allows the kernel to run the app as an init process
  • This is generally referred to by the abbreviation initrd.
  • initrd is an area of RAM that provides a storage device interface to the rest of the kernel.
• Since there were no questions, we attempted to make our minimal Linux distro interactive
  • We implemented a parameter allowing a user to specify a string to print after “hello” instead of “world”
  • The feature started working right in time for the end of class