Linux

• Find an open-source software that you're interested in, but your main distro doesn't provide it in the official repo. Be a packager for this software.
• Open your distro's wiki, rewrite (or contribute, if already good enough) a page or section.
• Try the bleeding-edge version (or very-early testing) of your favourite distro, and submit some test results, regarding to your hardware.

IMHO these tasks are interesting, could learn a lot from these tasks, and other linux users could benefit from these work

https://linuxjourney.com/

As an alternative idea…

A using a spare desktop as a headless VM server would be a good way to practice your CLI skills. Don’t install a GUI, or web admin tool, and only use SSH to admin it.

From there, setup a couple of VMs for Arch or Gentoo testing. Eventually, a Linux From Scratch attempt would provide a lot of learning opportunities.

This might be something for you https://linuxupskillchallenge.org/

"I’ve been considering installing Arch the traditional way, on my X220, as a way to force myself to improve."

I use Arch and so does my wife (she has no idea). The wiki is legendary because it is well used (I've written a few bits myself). I've used Gentoo for quite a while too but you will find compilation times a bit of a bore.

I own an IT company - I am the MD. I use Arch actually! (and so does my wife)

Manual arch install was one of the best experiences I had on Linux so far. You learn so much (even more when you try to compare file systems for example to find the best one for you) from the wiki. I don’t know if I’ll be switching from it haha. I’m in the same boat as you, wanting to learn it more and more, hell I’m reading How Linux Works book haha. CLI file management is nice, but I still go back to GUI a lot cos it’s easier to drag and drop to another window instead of figuring out the path to copy to. Not gonna use it just for the sake of it lol Unless someone has tips. I’m all ears :)

Installing arch is a great way to learn. Also don't be scared of daily driving it, it's not like it breaks twice a week. More like once a year, which is better than ubuntu in my experience.

Another vote for Arch. Manual Arch install was an interesting, and positive, experience. I did it multiple times so I could better understand what was actually being done. It helped me understand the boot and EFI partitions because I wanted to dual boot Windows.

For Arch itself, I've had a way snappier experience with pacman than apt and the AUR is a really convenient resource. So many packages there that you would otherwise have to build from source.

Bleeding edge packages can cause problems, but there are ways to recover. downgrade from the AUR makes downgrading packages really easy. The latest Nvidia drivers caused a bunch of problems with games for me on Wayland so I downgraded them and the Linux kernel and added them to pacman's package ignore list.

I really do recommend doing a Gentoo install at some point, because I think you would learn a lot from it. It’s a really nice experience and a well put together distro. The compiling is potentially not as bad as you think, but there are a couple of packages that are notoriously painful to compile (there are prebuilt binaries available for some of the painful ones if desired too). You’d probably get a decent amount out of an Arch install too. Arch isn’t my cup of tea, but lots of people like it and it’d be quicker to get started than Gentoo. I’m not sure I’d recommend it for you at this stage but eventually you should check out NixOS too! You can even try the package manager out on any distro you want. NixOS is really interesting, but it does things a bit different from other distros, and if you’ve done an Arch / Gentoo install it’ll be interesting to see what NixOS does in contrast.

Other things to mess with… You mention partitioning, so make sure to check out LVM, and also consider reading a bit about filesystems. Maybe give btrfs a go :).

I wouldn’t worry about daily driving either Gentoo or Arch. Once you have them set up you’ll probably be fine.

Try virtualization and containerization. Like Distrobox, running libvirt in one and a client in another. Or use ssh.

Harden your system, setup a secure ssh server for example

Installing Arch manually will teach you a lot of those things. Just do not use archinstall.

Arch is pretty painless on the long run, almost everything is available when you combine AUR and official. I've had some package manager issues after not using my laptop for like 6 months but I believe it more a lack for arch knowledge rather than a problem for intermediate / advanced user.

What was frustrating, like in every single imperative distro it that I feel like the system isn't clean anymore after a while and I end up reinstalling or hoping for another distro.

What I found to daily drive everything rock solid but in a funny way is NixOS, which is declarative. If you have some time and curiosity I would recommend checking how it works. No more distro hoping / installs for me

Not a joke:

Write your own device driver.

Preferably for some kind of esoteric hardware that you own but no-one else has, but it'd also be a valuable experience to do it for some commonly used piece of hardware for which good Linux drivers already exist.

For any moderately talented programmer this should be a reasonably difficult exercise, which will teach you very valuable lessons about Linux (and be quite fun at the same time).

Linux Bible 10th edition. Yes, it's for Fedora but use whatever distro you just prefer. It'll teach everything about Linux you need to know.

What is meant by "daily driving"?

I agree with what other people have said about using the command line more and the gui less, that will make you have to learn about utils like find, grep, sed, and maybe awk.

Try learning vim (or emacs). Use some command like tools for stuff you'd do in the gui. Try some basic scripting for common tasks. Maybe write some short python/ruby scripts if you need them. I've found that writing code has given me a need for learning more about how the command line works, and other "power user" features.

Alpine Linux might be good, too. It’s different. But that makes it a great exercise. See https://drewdevault.com/2021/05/06/Praise-for-Alpine-Linux.html

I've found that using GitHub Copilot CLI is a neat way go improve my CLI skills.

I ask and it explains commands to me.

https://githubnext.com/projects/copilot-cli

I first tried KDE Plasma 5 but tbh I thought it was just a worse experience than Win7, it was really close but all the tiny little annoyances got in the way and it felt like I couldn't do everything I needed through GUI so I still had to use terminal but it was awkward having to switch between using the keyboard and mouse and I would navigate through the GUI to get to directories then open terminal...

After a month or two of that I finally tried a tiling WM (i3wm) and it's just a way way better user experience than any DE.

I will note though that I'm using Fish for my interactive shell and seeing anything in the tiny dmenu was just way too hard until I used Rofi for drun.

Without Fish and Rofi I might've tried more DEs or even gone back to Win7.

I recently used Linux Mint with Cinnamon on a relative's PC and using Bash and the apt package manager sucks so bad. I even prefer Arch KDE, although I think Nemo is a bit better than Dolphin.

Anyway it's been about 2 years of daily driving Arch with i3wm for me and I haven't really gone out of my way to learn things but you naturally pick stuff up along the way just by using it.

Just make sure you've got another device with an internet connection in case something happens. I basically haven't had any issues after I got better but I made a lot of user errors at the start. Nothing that can't be fixed but finding out how to do the fixing without internet is a million times harder.