Many broken symlinks in `/nix/var/nix/gcroots/per-user/username`

[dschrempf]

Hi!

Whenever an existing nix-direnv profile is changed, the link to the old profile sticks around in /nix/var/nix/gcroots/per-user/username/... and becomes broken because the old profile is deleted by nix-direnv (at least this is the case for me, but see #235).

Is this behavior expected?

At the moment, I delete broken symlinks once every few months, but it is a bit tedious.

I think it is good that the old profile is deleted but I would prefer also deleting the old symlink to the old profile, which will become broken. Is this an option?

Thanks!

[Mic92]

At least in nixos, you can automate cleanup old profiles by doing:

{ nix.gc.automatic = true; }

Than your old links get deleted every day.

[dschrempf]

Weird, this is what I am using, but the direnv links stick.

EDIT: I have to use

cd /nix/var/nix/gcroots/per-user
find . -xtype l -print0 | xargs -0 rm

and a ton of stuff is removed.

[Mic92]

oh, I think you are right. nix-gc does only seem to cleanup profiles and not these gc roots. The current impact is that few inodes for symlinks are wasted. However the references sources are cleaned up.

[dschrempf]

Yes, I think so.

Funnily enough, the autoamtic garbage collection does remove stale links in /nix/var/nix/gcroots/auto.

[Mic92]

That's why I thought it would also do this for per-user ones...

[dschrempf]

Do you think I should open a brief issue at NixOS/nix?

[Mic92]

It might good to find out if upstream would be interested in this. Chances are, it leaves the cleanup to the application creating the gcroot in the first place.

[bbenne10]

I think that #246 should resolve this issue. @dschrempf could you try with latest master and report back?

[dschrempf]

I can confirm that the master version removes gcroot symlink for flakes. I did not test the feature for non-flake repositories! Thank you very much for implementing this feature! If the feature also works for normal repos, we should close it!

[bbenne10]

#246 was tested pretty thoroughly for the use nix usecase, so I think we're going to call this done.
Thanks for the testing (and for the upstream issue, which I think is probably still valid).

[sanerdsher]

Please reopen. I got the same issue on NixOS from nixos-unstable branch.

~ find -P /nix/var/nix/gcroots/per-user -xtype l 2>/dev/null | TZ=UTC xargs stat --printf="%N\ntime of file birth: %w\n\n"
'/nix/var/nix/gcroots/per-user/root/etc-nixos-.direnv-flake--inputs--26d6xg6m11gp22al1gxr1h8zdfmf9j94--source' -> '/etc/nixos/.direnv/flake-inputs//26d6xg6m11gp22al1gxr1h8zdfmf9j94-source'
time of file birth: 2023-04-24 09:21:18.551951038 +0000

'/nix/var/nix/gcroots/per-user/root/etc-nixos-.direnv-flake--inputs--dn0z0jnms4dpa78v3l10phw181dakw4x--source' -> '/etc/nixos/.direnv/flake-inputs//dn0z0jnms4dpa78v3l10phw181dakw4x-source'
time of file birth: 2023-04-24 09:21:18.565951076 +0000

'/nix/var/nix/gcroots/per-user/root/etc-nixos-.direnv-flake--inputs--4xqcsaqhvcvmvlrzx9hn7mwphw5iajav--source' -> '/etc/nixos/.direnv/flake-inputs//4xqcsaqhvcvmvlrzx9hn7mwphw5iajav-source'
time of file birth: 2023-04-24 09:21:18.578951111 +0000

'/nix/var/nix/gcroots/per-user/root/etc-nixos-.direnv-flake--inputs--n0fx19w1fj8bqwvc9pjn38px4jr2ps8r--source' -> '/etc/nixos/.direnv/flake-inputs//n0fx19w1fj8bqwvc9pjn38px4jr2ps8r-source'
time of file birth: 2023-04-24 09:21:18.318950413 +0000

'/nix/var/nix/gcroots/per-user/root/etc-nixos-.direnv-flake--inputs--flj71j7fyv4z4vpn53p836wy6ysbjyfw--source' -> '/etc/nixos/.direnv/flake-inputs//flj71j7fyv4z4vpn53p836wy6ysbjyfw-source'
time of file birth: 2023-04-24 09:21:18.448950762 +0000

~ nix --version
nix (Nix) 2.15.0

~ cat /etc/nixos/.envrc 
#!/usr/bin/env bash

local ver="2.3.0"
local user="nix-community"
local repo="nix-direnv"
local artifact="direnvrc"
local url="https://raw.githubusercontent.com/${user}/${repo}/${ver}/${artifact}"
local hash="sha256-Dmd+j63L84wuzgyjITIfSxSD57Tx7v51DMxVZOsiUD8="

if ! has nix_direnv_version || ! nix_direnv_version "${ver}"; then
  source_url "${url}" "${hash}"
fi

nix_direnv_watch_file \
  overlays/* \
  pkgs/* \
  shell/*
use flake || use nix

nix store gc doesn't remove such broken links.

[dschrempf]

Did you run this command as user or as root? I think only sudo nix-collect-garbage -d deletes the profiles of the root user.

[bbenne10]

@dschrempf is right: nix store gc won't do anything here, as you will only remove profiles for your user without sudo (and last I checked there were still some differences between nix-collect-garbage -d and nix store gc, but I couldn't tell you what they were off hand. I'll have to go dig into the differences between those tools soon)

Nix 2.15 should be creating gcroots in $XDG_DATA_DIR/nix/gcroots (which will be ~/.local/share/nix/gcroots), so if these were created both for this user and with this nix version, that is where I would expect them to go. However, it is clearly not for this user. The path ('/nix/var/nix/gcroots/per-user/root/...) states the name of the user for which the gcroot was created. Please try again with sudo.