--- debian/mdadm.postinst	2014-02-18 17:10:24.000000000 +0800
+++ debian//mdadm.postinst.new	2014-02-24 21:09:33.104987499 +0800
@@ -144,7 +144,7 @@
     update-rc.d mdadm-raid remove
 
     update-initramfs -u
-    if type update-grub; then
+    if type update-grub && [ -e /boot/grub/grub.cfg ]; then
         update-grub
     fi
     ;;