Hello. I can't seem to join https://matrix.to/#/#users:nixos.org . Evidently, I can't even show the screenshot of the error, which said "Failed to join
MatrixError: [403] You are not invited to this room. (https://kde.modular.im/_matrix/client/v3/join/!6oudZq5zJjAyrxL2uY%3A0upti.me)". I want to join so I can ask this question:

I'd like to debug this issue with systemd-remount-fs and, ultimately, libmount by using rr on a build of util-linux (which I believe contains libmount that system-remount-fs uses) that is unstripped and has debug symbols included, using nixseparatedebuginfod. How would I go about doing that? Do I just need to build and install a version of util-linux with separateDebugInfo set to true, e.g., by using the following flake:

{
  inputs = {
    disko = {
      url = "github:nix-community/disko";
    };
    nixpkgs = {
      url = "github:NixOS/nixpkgs/nixos-unstable";
    };
  };
  outputs =
    {
      disko,
      nixpkgs,
      self,
      ...
    }:
    let
      defaultUser = "nixos";
      hostName = "nixos";
      system = "x86_64-linux";
    in
    {
      diskoConfigurations = {
        ${hostName} = {
          disko = {
            devices = {
              disk = {
                vda = {
                  device = "/dev/vda";
                  type = "disk";
                  content = {
                    type = "gpt";
                    partitions = {
                      vda1 = {
                        type = "EF00";
                        size = "8G";
                        content = {
                          type = "filesystem";
                          format = "vfat";
                          mountpoint = "/boot";
                        };
                      };
                      vda2 = {
                        size = "100%";
                        content = {
                          type = "bcachefs";
                          filesystem = "bcachefs_a";
                          label = "group_a.vda2";
                        };
                      };
                    };
                  };
                };
              };
              bcachefs_filesystems = {
                bcachefs_a = {
                  type = "bcachefs_filesystem";
                  passwordFile = "/tmp/secret.key";
                  subvolumes = {
                    "subvolumes/root" = {
                      mountpoint = "/";
                    };
                  };
                };
              };
            };
          };
        };
      };
      nixosConfigurations = {
        ${hostName} = (
          nixpkgs.lib.nixosSystem {
            inherit system;
            modules = [
              (
                {
                  config,
                  inputs,
                  lib,
                  pkgs,
                  ...
                }:
                {
                  boot = {
                    kernelPackages = pkgs.linuxPackages_testing;
                    loader = {
                      efi = {
                        canTouchEfiVariables = true;
                      };
                      systemd-boot = {
                        enable = true;
                      };
                    };
                  };
                  console = {
                    keyMap = "uk";
                  };
                  environment = {
                    systemPackages = [
                      pkgs.rr
                      pkgs.util-linux.overrideAttrs (after: before: {
                        separateDebugInfo = true;
                      })
                    ];
                  };
                  i18n = {
                    defaultLocale = "en_GB.UTF-8";
                    extraLocaleSettings = {
                      LC_ADDRESS = "en_GB.UTF-8";
                      LC_IDENTIFICATION = "en_GB.UTF-8";
                      LC_MEASUREMENT = "en_GB.UTF-8";
                      LC_MONETARY = "en_GB.UTF-8";
                      LC_NAME = "en_GB.UTF-8";
                      LC_NUMERIC = "en_GB.UTF-8";
                      LC_PAPER = "en_GB.UTF-8";
                      LC_TELEPHONE = "en_GB.UTF-8";
                      LC_TIME = "en_GB.UTF-8";
                    };
                  };
                  imports = [
                    ./hardware-configuration.nix
                  ];
                  networking = {
                    inherit hostName;
                    networkmanager = {
                      enable = true;
                    };
                  };
                  programs = {
                    git = {
                      enable = true;
                    };
                  };
                  nix = {
                    settings = {
                      experimental-features = [
                        "nix-command"
                        "flakes"
                      ];
                    };
                  };
                  services = {
                    xserver = {
                      xkb = {
                        layout = "gb";
                        variant = "";
                      };
                    };
                    nixseparatedebuginfod = {
                      enable = true;
                    };
                  };
                  time = {
                    timeZone = "Europe/London";
                  };
                  users = {
                    users = {
                      ${defaultUser} = {
                        description = "NixOS";
                        extraGroups = [
                          "networkmanager"
                          "wheel"
                        ];
                        isNormalUser = true;
                        packages = [ ];
                      };
                    };
                  };
                  system = {
                    stateVersion = "25.05";
                  };
                }
              )
              self.diskoConfigurations.${hostName}
              disko.nixosModules.disko
            ];
          }
        );
      };
    };
}

Or do I need to do something else to get systemd-remount-fs to use that version of util-linux?

yeah. there have been a few cases where:

• someone can't join the room because it's invite-only
• I can't invite them; server refuses because they're already in the room
• I can't kick them; same server refuses because they're not in the room