Elliott Fournier-Robert

October ISO

Github repository: october-iso

It is good to have an installer, but installing an operating system will basically wipe the existing OS and replace it with the new one. You can see how wiping the OS that is executing the program that installs the new OS doesn’t work. It’s a snake eating its own tail. To solve this problem, we need to have an external bootable drive that the computer can boot on and execute the installer on.

During the 1980s, people used floppy disks for this. One floppy disk would be bootable, then the installer would tell you to put another floppy in to continue the installation, then another and then the next one until the process of installing is done. Then, during the 1990s, this operation was done from a CD-ROM and the 2000s replaced those with DVDs.

During this time, a file format was created which is called Optical disc image or ISO image. An ISO file is, basically, a virtualized version of an optical drive file system. This file is like another file and it can be passed around, copied on other drives etc. Operating systems quickly became able to use it just like any optical drives.

By the 2010s, this quickly became the standard way of distributing operating systems installation media. You could make a bootable USB drive with an ISO file on it and then boot on it easily just like you would with an optical drive. Since it is just a file, some tools lets you have multiple ISOs simultaneously on a single drive.

Today, October Linux has its own ISO repository that can generate a fully working ISO file. It contains both the installer and the list of packages that will be installed on top of a basic Arch Linux installation.

Generating an ISO

The repository contains a folder called archiso. This folder has an airootfs profile. Airootfs lets us define files and folders just like it should be inside the ISO and it will copy them over while generating an image. Basically, the folder airootfs is our profile root folder (/).

To generate a new ISO, we have a small script called mkiso.sh. When executed with no arguments, it will create a development image. This image assumes you are executing it through a QEMU virtual machine and it will try to mount a folder on the host machine assumed to contain the code of the installer. When executed with the argument “release”, it will create a release ISO containing the latest release of the installer.

The release script works in three steps:

  1. It copies the package list from the documentation folder to airootfs.
  2. Pulls the latest release of the installer, from Github, and puts the binary inside /usr/bin of the airootfs.
  3. It calls mkarchiso and gives it the profile on the repository so that it can generate an image for us.

This is how we generate an ISO image of October Linux. Then, you can just flash a USB drive with it using a software like Ventoy or dd and you’re good to go.