Describe the bug
A clear and concise description of what the bug is.

To Reproduce
Steps to reproduce the behavior:

1. $ nix-env -iA nixos.virtmanager
2. change some config, for example add a connection
3. close virt-manager
4. reopen virt-manager

Expected behavior
config is preserved through restarts of application

Additional context
Fix: $ nix-env -iA nixos.gnome3.dconf

Metadata

• system: "x86_64-linux"
• host os: Linux 4.19.57, NixOS, 19.03.173389.51e1e3ceaf0 (Koi)
• multi-user?: yes
• sandbox: yes
• version: nix-env (Nix) 2.2.2
• channels(root): "nixos-19.03.173389.51e1e3ceaf0"
• nixpkgs: /nix/var/nix/profiles/per-user/root/channels/nixos

Maintainer information:

# a list of nixpkgs attributes affected by the problem
attribute: nixpkgs/pkgs/applications/virtualization/virt-manager/default.nix
# a list of nixos modules affected by the problem
module: