The new tarballBuilder trap fails when trying to remove /var/empty.

[terlar]

Bug description

I recently tried migrating over to the new tarballBuilder. However when I try to execute the script I get the following error:

rm: cannot remove '/tmp/nixos-wsl-tarball.H3cpgOr2Np/var/empty': Operation not permitted

Apparently that folder is marked as immutable, even preventing root from removing it, however it can be solved by:

chattr -i /tmp/nixos-wsl-tarball.H3cpgOr2Np/var/empty

To Reproduce

Steps to reproduce the behavior:

sudo nix run --print-build-logs github:nix-community/NixOS-WSL#nixosConfigurations.modern.config.system.build.tarballBuilder

Expected behavior
Not failing on the trap after script execution.

Logs

Include relevant console logs

...
installing the boot loader...
setting up /etc...
setting up /bin...
setting up /bin/login...
setting up /sbin/init shim...
installation finished!
[NixOS-WSL] Adding channel...
setting up /etc...
setting up /bin...
setting up /bin/login...
setting up /sbin/init shim...
[NixOS-WSL] Adding default config...
[NixOS-WSL] Compressing...
rm: cannot remove '/tmp/nixos-wsl-tarball.xXcwgyysE7/var/empty': Operation not permitted

[terlar]

I got it working like this:

diff --git a/modules/build-tarball.nix b/modules/build-tarball.nix
index 8341f7f..4cdd3e5 100644
--- a/modules/build-tarball.nix
+++ b/modules/build-tarball.nix
@@ -64,7 +64,7 @@ in

         root=$(mktemp -p "''${TMPDIR:-/tmp}" -d nixos-wsl-tarball.XXXXXXXXXX)
         # FIXME: fails in CI for some reason, but we don't really care because it's CI
-        trap 'rm -rf "$root" || true' INT TERM EXIT
+        trap 'chattr -Rf -i "$root" || true && rm -rf "$root" || true' INT TERM EXIT

         chmod o+rx "$root"

or

diff --git a/modules/build-tarball.nix b/modules/build-tarball.nix
index 8341f7f..3d787ab 100644
--- a/modules/build-tarball.nix
+++ b/modules/build-tarball.nix
@@ -64,7 +64,7 @@ in

         root=$(mktemp -p "''${TMPDIR:-/tmp}" -d nixos-wsl-tarball.XXXXXXXXXX)
         # FIXME: fails in CI for some reason, but we don't really care because it's CI
-        trap 'rm -rf "$root" || true' INT TERM EXIT
+        trap 'chattr -i "$root/var/empty" || true && rm -rf "$root" || true' INT TERM EXIT

         chmod o+rx "$root"

[nzbr]

Can you make this, as well as #338 into a PR?

[terlar]

Sure, I will do