slock

Setup

To make slock available, amend /etc/nixos/configuration.nix as follows:

{
  ...
  programs.slock.enable = true;
  ...
}

Troubleshooting

"cannot disable the out-of-memory killer for this process"

slock requires root for accessing passwords and protecting itself from OOM killing. Adding slock to environment.systemPackages is not adequate (nor is it necessary); slock should be enabled via the provided NixOS module via the means shown above.