I’ve found a similar report from a while ago related to the Nix manual, but nothing else.
This is the output I get:
$ nixos-version
24.05pre-git (Uakari)
My NixOS configuration is based on flakes, is there any particular configuration needed to get the Git hash in the version back?
Here’s the script that looks for @version@: nixpkgs/nixos/modules/installer/tools/nixos-version.sh at 5c0c6e14926c39d5c90073f01ca7fa6d24e3671b · NixOS/nixpkgs · GitHub
If I understand correctly, this is the script used to get that version: nixpkgs/nixos/modules/installer/tools/get-version-suffix at 5c0c6e14926c39d5c90073f01ca7fa6d24e3671b · NixOS/nixpkgs · GitHub
Running the command to get the nixpkgs instance as that script I get this:
$ nix-instantiate --find-file nixpkgs "$@"
/nix/store/nra828scc8qs92b9pxra5csqzffb6hpl-source
Which doesn’t actually have a .git folder that the script is trying to find to get the revision:
$ ls -la /nix/store/nra828scc8qs92b9pxra5csqzffb6hpl-source
total 27120
dr-xr-xr-x 8 root root 4096 Jan 1 1970 .
drwxrwxr-t 26902 root nixbld 27635712 May 10 13:16 ..
-r--r--r-- 2 root root 36168 Jan 1 1970 CONTRIBUTING.md
-r--r--r-- 6 root root 1097 Jan 1 1970 COPYING
-r--r--r-- 25 root root 971 Jan 1 1970 default.nix
dr-xr-xr-x 15 root root 4096 Jan 1 1970 doc
-r--r--r-- 5 root root 2916 Jan 1 1970 .editorconfig
-r--r--r-- 5 root root 4353 Jan 1 1970 flake.nix
-r--r--r-- 12 root root 662 Jan 1 1970 .gitattributes
-r--r--r-- 3 root root 3289 Jan 1 1970 .git-blame-ignore-revs
dr-xr-xr-x 4 root root 4096 Jan 1 1970 .github
-r--r--r-- 2 root root 524 Jan 1 1970 .gitignore
dr-xr-xr-x 6 root root 4096 Jan 1 1970 lib
-r--r--r-- 7 root root 950 Jan 1 1970 .mailmap
dr-xr-xr-x 3 root root 4096 Jan 1 1970 maintainers
dr-xr-xr-x 7 root root 4096 Jan 1 1970 nixos
dr-xr-xr-x 20 root root 4096 Jan 1 1970 pkgs
-r--r--r-- 5 root root 5186 Jan 1 1970 README.md
lrwxrwxrwx 5 root root 12 Jan 1 1970 .version -> lib/.version
If this is the actual script, then it seems to be making wrong assumptions, no?
If you use legacyPackages, the version info should be detected automatically:
If you create custom Nixpkgs instance, you can change system.configurationRevision NixOS option, example:
Thank you! That points me in the right direction 
Any reason why you’re using self.rev there? I just tried to set it to inputs.nixpkgs.rev but it didn’t change anything even after rebooting…
FWIW I also tried doing the same as you (setting system.configurationRevision) without success, nixos-version still reports the same output 
Another thing I tried was to set this option when I instantiate nixpkgs:
pkgs = import inputs.nixpkgs {
inherit overlays system;
config.allowUnfree = true;
config.system.configurationRevision = inputs.nixpkgs.rev or "dirty-${inputs.nixpkgs.lastModifiedDate}";
};
Still no luck…
Ah, sorry I misremembered. What I am doing is to get nixos-version --configuration-revision. Just nixos-version works for me without any special considerations:
$ nixos-version
24.05.20240507.b211b39 (Uakari)
But checking my Nixpkgs instance, it does not have the info you want either:
nix-repl> :lf /home/jtojnar/Projects/nixfiles
Added 17 variables.
nix-repl> outputs.legacyPackages.x86_64-linux.lib.version
"24.05pre-git"
I have updated my flake to provide this information.
But the fact that nixos-version shows the correct revision even without that probably means that I am using nixpkgs.lib somewhere instead of lib from my overlaid Nixpkgs. Edit: I do that here:
Thank you! I just realized I needed that overlay too because I’m extending lib as well, so I’ve come to the same solution 
Hmm, looks like the difference between our configs is that you are passing lib to nixosSystem, whereas I did not do that:
As a result nixosSystem fell back to nixpkgs.lib on my system:
That’s correct, because I have a few custom lib functions. Fixed here by extending the versions overlay