install mount_union setuid root. permission checks are done in the kernel.

[unix-history] / usr / src / sbin / mount_union / Makefile

#       @(#)Makefile    8.2 (Berkeley) %G%

CFLAGS+=-I/sys
PROG=   mount_union
MAN8=   mount_union.0
BINOWN= root
BINMODE=4555

.include <bsd.prog.mk>