How to use spaces in system.nixos.label / NIXOS_LABEL

rssaromeo · February 21, 2026, 11:09pm

I’ve tried setting NIXOS_LABEL_VERSION and NIXOS_LABEL and when adding a space it fails to build.

on the boot menu i see that there is spaces in the default boot entries like with “NixOS (Generation 2…” so why can system.nixos.label not contain spaces?

is it intended to use nixos-rebuild -p, from reading the docs about -p it appears that it is not renaming the entry but creating a folder for new entries and adding a new entry into it.

this is the update script i’m trying to use this in: nixconf/home/shellScripts/update/main.sh at ded106391eae6c4e245884f13aefc0959470ea4b · rsa17826/nixconf · GitHub

magicquark · February 27, 2026, 10:43pm

The documentation for the option, by omission, states that you cannot use spaces.

github.com/NixOS/nixpkgs

nixos/modules/misc/label.nix

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          It can only contain letters, numbers and the following symbols:
          `:`, `_`, `.` and `-`.

magicquark · February 27, 2026, 10:46pm

The full string is generated in the file below. Presumably you would have to modify some of the generation code to achieve what you want.

github.com/NixOS/nixpkgs

nixos/modules/system/boot/loader/systemd-boot/systemd-boot-builder.py

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          BOOT_ENTRY = """title {title}
          sort-key {sort_key}
          version Generation {generation} {description}
          linux {kernel}
          initrd {initrd}
          options {kernel_params}
          """