I hopped from arch (2010-2019) to Nixos (2019-2023). I had my issues with it but being a functional programmer, I really liked the declarative style of configuring your OS. That was until last week. I decided to try out void Linux (musl). I'm happy with it so far.
Why did I switch?
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Nix is extremely slow and data intensive (compared to xbps). I mean sometimes 100-1000x or more. I know it is not a fair comparison because nix is doing much more. Even for small tweaks or dependency / toolchain update it'll download/rebuild all packages. This would mean 3-10GB (or more) download on Nixos for something that is a few KB or MB on xbps.
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Everything is noticeably slower. My system used way more CPU and Ram even during idle. CPU was at 1-3% during idle and my battery life was 2 to 3.5h. Xfce idle ram usage was 1.5 GB on Nixos. On Void it's around 0.5GB. I easily get 5-7h of battery life for my normal usage. It is 10h-12h if I am reading an ebook.
Nix disables a lot of compiler optimisations apparently for reproducibility. Maybe this is the reason?
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Just a lot of random bugs. Firefox would sometimes leak memory and hang. I have only 8 GB of ram. WiFi reconnecting all the time randomly. No such issues so far with void.
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Of course the abstractions and the language have a learning curve. It's harder for a beginner to package or do something which is not already exposed as an option. (This wasn't a big issue for me most of the time.)
For now, I'll enjoy the speed and simplicity of void. It has less packages compared to nix but I have flatpak if needed. So far, I had to install only Android studio with it.
My verdict is to use Nixos for servers and shared dev environments. For desktop it's probably not suitable for most.
Yeah rollbacks are probably the best part of immutable OS's, but of almost equal importance is reproducible system configuration, which imo only Nix and Guix do well. Neither snapshots nor Silverblue really manage that yet.
For reproducible configuration in the Arch world, there's a project which always looks good to me: aconfmgr
https://github.com/CyberShadow/aconfmgr
I think Arch+aconfmgr+yadm+btrfs == a pretty solid arrangement.
Though I'm of course itching for first class Bcachefs support...
Yeah. For reproducibility I still use nix. Especially when I have to share my dev environment with a team or to spin up identical servers.
Can you give an example in what kind of scenario you would want "identical servers"? In my head that is where tools like ansible come into play..?
You can achieve similar results with ansible. But I like nix better. It is reproducible. You can think of it like docker.
Nix is also declarative and has rollback. Also, nixos-rebuild is idempotent.
The great thing about Nix is that it achieves reproducibility with the package manager. Container and Ansible depend on taking a system and documenting steps to bring it to the desired state. This state then might deviate over time (e.g. crashing while updating).
But yes, for most practical use it probably doesn't make much of a difference. For me Nix forces me to document what I'm doing, which I might not do for "quick and simple change" on other systems.