It may be useful to see what Nix does. Nix has many static id, with the comment: # IMPORTANT! # We only add static uids and gids for services where it is not feasible # to change uids/gids on service start, in example a service with a lot of # files. Please also check if the service is applicable for systemd's https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/misc/ids.nix