Remove perl dependency in activation scripts

[andrewchambers]

Issue description

Approximately 10 percent of a minimal nixos install is perl, perhaps we could remove this somehow.

Not critical, feel free to close the issue if this is not the right place for that.

Steps to reproduce

Use a config like:

{ config, lib, ... }:
{
    imports = [
        <nixpkgs/nixos/modules/profiles/minimal.nix>
        <nixpkgs/nixos/modules/profiles/headless.nix>
        <nixpkgs/nixos/modules/profiles/qemu-guest.nix>
    ];

    fileSystems."/" = {
      device = "/dev/disk/by-label/nixos";
      autoResize = true;
    };

    boot.growPartition = true;
    boot.loader.grub.device = "/dev/sda";
    boot.kernelParams = [ "console=ttyS0" "panic=1" "boot.panic_on_fail" ];
    boot.initrd.kernelModules = [ "virtio_scsi" ];
    boot.kernelModules = [ "virtio_pci" "virtio_net" ];

}

Run

nixos-rebuild build -I nixos-config="./configuration.nix"
du -sch $(nix-store -qR ./result) | sort -h

And see the second largest dependency is perl:

...
56M     /nix/store/q9ajsngf2w3r10dg7b1148wzq1avp4gj-perl-5.28.0
70M     /nix/store/cs0lixjvndy2z4gby1nvmnzdd4jkmi02-linux-4.14.81
597M    total

[ac@black:~/src/minimal-nixos]$ nix why-depends ./result /nix/store/q9ajsngf2w3r10dg7b1148wzq1avp4gj-perl-5.28.0
/nix/store/zazd30c454axi23z00qr5q7y3rvzzvvd-nixos-system-nixos-18.09pre-git
╚═══activate: …ll -m 0755 -d /home../nix/store/q9ajsngf2w3r10dg7b1148wzq1avp4gj-perl-5.28.0/bin/perl -w \.  -I/…
    => /nix/store/q9ajsngf2w3r10dg7b1148wzq1avp4gj-perl-5.28.0

Looking further, the two uses of perl are

/nix/store/1hkp2n6hz3ybf2rvkjkwrzgbjkrrakzl-update-users-groups.pl
and /nix/store/vn1xs9s2akf79y1pbya2qldydbf2b22m-setup-etc.pl .

So a few hundred lines of perl are taking up 10 percent of the base install.

[jtojnar]

Is it really an issue? See also #48378 for similar discussion.

[andrewchambers]

It affects provisioning and boot times of VM's - Am investigating now to what degree, will report back with some results on google cloud platform and others using a tiny image I built today.

[stale]

Thank you for your contributions.

This has been automatically marked as stale because it has had no activity for 180 days.

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[xaverdh]

I made an attempt at rewriting setup-etc.pl in rust here. This is also my first program in rust ever, so please don't blindly run this on your system as root (just yet).
suggestions / help / reviews are welcome!

[xaverdh]

Ah the repository should be public now (I forgot about gitlab defaults to creates them as private..)

[Gaelan]

I'm all for Rust in general, but I'm not sure we want activation scripts in a compiled language.

Activation scripts are one of the few "moving parts" of a NixOS system, and I imagine there are a lot of situations where the ability to easily read, debug, and edit them would help with recovering from weird bugs. I've never personally ended up in such a situation, so it'd be interesting to hear from anyone who has.

[Gaelan]

I suppose this is less of a problem if it's just a prebuilt binary configured via arguments/environment/config file/etc instead of something like the current perl script that's partially dynamically generated.

[stale]

I marked this as stale due to inactivity. → More info

[AkechiShiro]

@Gaelan So is a Rust pre-built binary something of interest or not worth it at all ?

[otavio]

I'd love to see this moving forward; this reduces the size of minimal images and helps to boost the maintenance in long term.

[zimbatm]

This is now possible thanks to nikstur's work. See #270727 and follow-ups.