# Get a list of channels. $ nix-channel --list nixpkgs https://nixos.org/channels/nixpkgs-unstable # Add and remove channels (doesn't update) $ nix-channel --remove nixpkgs $ nix-channel --add https://nixos.org/channels/nixos-18.03 nixpkgs # Download current version of channel. $ nix-channel --update # Update all packages. $ nix-env -u '*' So it should now be the same as gwtest? No. Doing the same there. So, to pin everything, create a custom channel? I still don't understand the difference between a direct link to nixpkgs tree in a default.nix file, and a channel. https://www.reddit.com/r/NixOS/comments/4btjnf/fully_setting_up_a_custom_private_nix_repository/ It appears that the <nixpkgs> is the entry name in the nix-channel list.