82 lines
4.4 KiB
Markdown
82 lines
4.4 KiB
Markdown
# making custom arch linux live ISOs without arch linux
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2023-06-07
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If you've ever installed any Linux distro, you probably had to do it using a live install environment.
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Once you flashed the USB drive, you could boot off it and you'd be greeted with a Linux system.
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I've always found it fascinating that you could pack the entire OS onto a stick and bring it around with you.
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However, something even more enticing is being able to customize that system.
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This is where archiso comes in handy:
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it's a tool that can be used to generate ISOs with Arch Linux on them.
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You can flash these ISOs to USB drives to make portable Arch Linux systems.
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archiso is also incredibly flexible, and you can customize it very well.
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In fact, it's the tool that Arch's maintainers use to generate the official live installation images.
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The one issue I have, though is that you need to be running Arch Linux to run archiso:
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> "Currently creating the images is only supported on Arch Linux but may work on other operating systems as well."
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As I run another distro on my laptop, I could not use archiso.
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So, in the last few days, I set out to make archiso run on my system.
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The final results of this endeavour can be found [on GitHub](https://github.com/dogeystamp/archiso-portable).
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## pacstrap
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One of the essential dependencies of archiso is pacstrap.
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Essentially, what pacstrap does is that it creates a small Arch Linux system in a folder.
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This is the bootstrapped root filesystem (root FS).
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Later, archiso takes that folder, compresses it, and puts it in the final ISO file.
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The problem is that pacstrap needs your host system to be Arch Linux so that it can bootstrap a new Arch system.
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In fact, if you look at the [source code](https://github.com/archlinux/arch-install-scripts/blob/master/pacstrap.in),
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you'll find that the host system uses its own pacman to install everything to the bootstrapped system:
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pacman -r "$newroot" "${pacman_args[@]}"
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pacstrap only has to create a few directories, but the rest is done by installing the `base` metapackage through pacman.
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`base` includes both `filesystem` and `pacman`.
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As far as I understand, this means that all the important files in an Arch Linux system come from installing the `filesystem` package.
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Once the host pacman installs `base` in the bootstrapped system, we have a full Arch Linux root FS, including its own pacman.
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However, since I do not have pacman to bootstrap this way, I needed another way to obtain an Arch root FS.
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I came across [archstrap](https://github.com/wick3dr0se/archstrap), which does exactly that.
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archstrap downloads a pre-built Arch Linux root FS as a tarball, then installs packages to it just like regular pacstrap.
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Cleverly, this script removes the need for arch-chroot on the host system:
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it runs the arch-chroot inside the downloaded Arch filesystem.
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Somewhat annoyingly though, archstrap does not operate exactly the same way pacstrap does:
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I had to patch it to get it working with archiso.
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Also, I patched archiso itself to remove some flags archstrap doesn't parse.
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## other changes
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The other main dependency missing in archiso is pacman, Arch's package manager.
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Since we aren't running Arch, we of course do not have it on our host system.
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However, the bootstrapped Arch root FS we downloaded earlier does have pacman inside of it.
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Therefore, I replaced all invocations of pacman inside archiso with invocations of the bootstrapped pacman.
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archiso also includes a small script to test your generated ISOs in a QEMU virtual machine.
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I added a check to it that switches some hard-coded paths.
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In Arch, the path is `/usr/share/edk2-ovmf/x64`,
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but on my system it was at `/usr/share/edk2-ovmf`.
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## conclusion
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It turns out that modifying open source software isn't that difficult.
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Given that archiso's maintainers wrote very structured and organized code,
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it's surprisingly easy to navigate around the script to patch things.
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Of course, I definitely ruined the quality of archiso by doing this:
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there's missing features and everything is untested and unlinted.
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Then again, this isn't going to be production-grade software;
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I just wanted to make a custom portable Arch USB while using Gentoo on my PC.
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Anyways, if you want to make your own custom Arch USBs but don't have Arch,
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check out [archiso-portable](https://github.com/dogeystamp/archiso-portable) on GitHub.
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As a bonus, here's a screenshot of the Arch Linux live environment I made earlier on a Gentoo system:
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