A list of paths bind-mounted into Nix sandbox environments. You can use the syntax target=source to mount a path in a different location in the sandbox; for instance, /bin=/nix-bin will mount the path /nix-bin as /bin inside the sandbox. If source is followed by ?, then it is not an error if source does not exist; for example, /dev/nvidiactl? specifies that /dev/nvidiactl will only be mounted in the sandbox if it exists in the host filesystem.

If the source is in the Nix store, then its closure will be added to the sandbox as well.

Depending on how Lix was built, the default value for this option may be empty or provide /bin/sh as a bind-mount of bash.