Rear behaves as expected. Did you check out there documentation ? http://relax-and-recover.org/documentation/
mkrescue as parameter will only create a boot media which you can use to recover the saved data itself. You will need to use a second HDD (may be USB) or simply a NAS to store your backup. Then run rear with parameter
mkbackup. It is also important to run rear as root. Like this: sudo usr/sbin/rear -v mkbackup HTH, D$
