+ # vboxguestdrivers/5.2.6-r0/vbox_module/vboxguest/Makefile.include.header:99: *** The variable KERN_DIR must be a kernel build folder and end with /build without a trailing slash, or KERN_VER must be set. Stop.
+ # vboxguestdrivers/5.2.6-r0/vbox_module/vboxguest/Makefile.include.header:108: *** The kernel build folder path must end in <version>/build, or the variable KERN_VER must be set. Stop.