# Build-dates of older nixos gnerations were changed after executing nix-store --optimise

**URL:** https://discourse.nixos.org/t/build-dates-of-older-nixos-gnerations-were-changed-after-executing-nix-store-optimise/73809
**Category:** Help
**Created:** [December 30, 2025, 1:09pm UTC](https://discourse.nixos.org/t/build-dates-of-older-nixos-gnerations-were-changed-after-executing-nix-store-optimise/73809 "2025-12-30T13:09:46Z")
**Posts on this page:** 1
**Showing post:** 2

<div class="post-metadata">

### Author: ![waffle8946](https://discourse.nixos.org/user_avatar/discourse.nixos.org/waffle8946/32/27221_2.png) [@waffle8946](https://discourse.nixos.org/u/waffle8946)
#### Post date: [December 30, 2025, 5:27pm UTC](https://discourse.nixos.org/t/build-dates-of-older-nixos-gnerations-were-changed-after-executing-nix-store-optimise/73809/2 "2025-12-30T17:27:42Z")

</div>

Known bug

> <https://github.com/NixOS/nixpkgs/issues/435555>
>
> \### Nixpkgs version
> 
> \- Unstable (25.11)
> 
> \### Describe the bug
> 
> The output of \`ni…xos-rebuild list-generations\` shows wrong build dates compared to \`nix-env\` and the timestamps in \`/nix/var/nix/profiles\` after using \`nix store optimise\`.
> 
> \### Steps to reproduce
> 
> \- Build a few generations
> \- Use \`nix store optimise\`
> 
> \### Expected behaviour
> 
> The output should be consistent regarding the build dates
> 
> \### Screenshots
> 
> \_No response\_
> 
> \### Relevant log output
> 
> \`\`\`console
> ❯ sudo nixos-rebuild list-generations
> Generation Build-date NixOS version Kernel Configuration Revision Specialisation Current
> 169 2025-08-21 13:17:45 25.11.20250819.2007595 6.16.1-cachyos Unknown \[\] True
> 168 2025-08-20 20:37:08 25.11.20250819.2007595 6.16.1-cachyos Unknown \[\] False
> 167 2025-08-20 20:37:24 25.11.20250819.2007595 6.16.1-cachyos Unknown \[\] False
> 166 2025-08-20 20:37:39 25.11.20250814.fbcf476 6.16.1-cachyos Unknown \[\] False
> 
> ❯ sudo nix-env --list-generations --profile /nix/var/nix/profiles/system
> 166 2025-08-19 20:38:05   
> 167 2025-08-20 13:50:53   
> 168 2025-08-20 20:35:22   
> 169 2025-08-21 13:17:46 (current)
> 
> ❯ sudo ls -l /nix/var/nix/profiles/
> total 20
> lrwxrwxrwx 1 root root 43 Mai 3 22:05 default -\> /nix/var/nix/profiles/per-user/root/profile
> drwxr-xr-x 3 root root 4096 Mai 3 14:16 per-user
> lrwxrwxrwx 1 root root 15 Aug 21 13:17 system -\> system-169-link
> lrwxrwxrwx 1 root root 83 Aug 19 20:38 system-166-link -\> /nix/store/yxc3hwyz0y07wjs5gp9frdp5kypcdyjg-nixos-system-dan-25.11.20250814.fbcf476
> lrwxrwxrwx 1 root root 83 Aug 20 13:50 system-167-link -\> /nix/store/rywn7g9vq7j2b0y7a4j8yc2cd62f9r2j-nixos-system-dan-25.11.20250819.2007595
> lrwxrwxrwx 1 root root 83 Aug 20 20:35 system-168-link -\> /nix/store/lc3zzj2q32ra8nzgw1fhfmq92q52hsic-nixos-system-dan-25.11.20250819.2007595
> lrwxrwxrwx 1 root root 83 Aug 21 13:17 system-169-link -\> /nix/store/i557rl9y7y7zvbqn9zanw0xxy0vfa4k4-nixos-system-dan-25.11.20250819.2007595
> \`\`\`
> 
> \### Additional context
> 
> \_No response\_
> 
> \### System metadata
> 
> - system: \`"x86\_64-linux"\`
> - host os: \`Linux 6.16.1-cachyos, NixOS, 25.11 (Xantusia), 25.11.20250819.2007595\`
> - multi-user?: \`yes\`
> - sandbox: \`yes\`
> - version: \`nix-env (Nix) 2.28.4\`
> - channels(root): \`""\`
> - nixpkgs: \`/nix/store/pxnx7dbr0pz3qpgw2r315wdbb00afdw7-source\`
> 
> \### Notify maintainers
> 
> 
> 
> \---
> 
> \*\*Note for maintainers:\*\* Please tag this issue in your pull request description. (i.e. \`Resolves #ISSUE\`.)
> 
> 
> \### I assert that this issue is relevant for Nixpkgs
> 
> \- \[x\] I assert that this is a bug and not a support request.
> \- \[x\] I assert that this is not a \[duplicate of an existing issue\](https://github.com/NixOS/nixpkgs/issues?q=is%3Aopen+is%3Aissue+label%3A%220.kind%3A+bug%22+-label%3A%226.topic%3A+darwin%22+-label%3A%226.topic%3A+nixos%22). 
> \- \[x\] I assert that I have read the \[NixOS Code of Conduct\](https://github.com/NixOS/.github/blob/master/CODE\_OF\_CONDUCT.md) and agree to abide by it.
> 
> \### Is this issue important to you?
> 
> Add a :+1: \[reaction\] to \[issues you find important\].
> 
> \[reaction\]: https://github.blog/2016-03-10-add-reactions-to-pull-requests-issues-and-comments/
> \[issues you find important\]: https://github.com/NixOS/nixpkgs/issues?q=is%3Aissue+is%3Aopen+sort%3Areactions-%2B1-desc

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