-apt_keys:
- -chroot "$@" apt-key add - <./raspbian-archive-keyring.gpg
- -chroot "$@" apt-key add - <./raspberrypi-archive-keyring.gpg
- -chroot "$@" apt-key add - <./debian-archive-stretch-stable.gpg
+apt_keys: raspi_root
+ -chroot "$<" apt-key add - <./raspbian-archive-keyring.gpg
+ -chroot "$<" apt-key add - <./raspberrypi-archive-keyring.gpg
+ -chroot "$<" apt-key add - <./debian-archive-stretch-stable.gpg