The solution is to give write access for the playground not to the users, but to a special Unix group such as games. Then chown the executable to user root, group games and set the setgid bit. When the game starts, the system will set the effective group id to games and NetHack will have the priveleges necessary to write to the playground. This sort of arrangement dates back to Hack, which needed this setup for the same reasons as NetHack does. Here is Hack 1.0.3 upon Kernigh's OpenBSD system: