Index: usr.sbin/freebsd-update/freebsd-update.sh
===================================================================
--- usr.sbin/freebsd-update/freebsd-update.sh
+++ usr.sbin/freebsd-update/freebsd-update.sh
@@ -2628,6 +2628,37 @@
 	echo "To install the downloaded upgrades, run \"$0 install\"."
 }
 
+# Perform system sanity checks to ensure
+# the file system can be modified as expected
+install_verify_system () {
+	_IS_RW="*[[:space:]]rw[[:space:]]*"
+	_IS_NFS="*[[:space:]]nfs[[:space:]]*"
+	# Verify the file system is not NFS otherwise chflags will not work,
+	# then verify that there are read-write permissions
+	# on required directories
+	for required_dir in / /usr /boot; do
+		mounted_dir=`df -T ${BASEDIR}/${required_dir} |
+		    sed -E 's,[[:blank:]]+, ,g' |
+		    cut -d' ' -f7`
+		case `mount -p ${mounted_dir}` in
+		$_IS_NFS)
+			echo -n "${BASEDIR}/${required_dir} "
+			echo -n "is on NFS (${mounted_dir}) "
+			echo "so chflags will not be supported."
+			echo "Update the source filesystem and then export it."
+			;;
+		$_IS_RW)
+			;;
+		*)
+			echo -n "${BASEDIR}/${required_dir} "
+			echo -n "is not on a file system (${mounted_dir}) mounted "
+			echo "with read-write permissions."
+			return 1
+			;;
+		esac
+	done
+}
+
 # Make sure that all the file hashes mentioned in $@ have corresponding
 # gzipped files stored in /files/.
 install_verify () {
@@ -2978,6 +3009,8 @@
 # Actually install updates
 install_run () {
 	echo -n "Installing updates..."
+	# Make sure the system is configured correctly
+	install_verify_system || return 1
 
 	# Make sure we have all the files we should have
 	install_verify ${BDHASH}-install/INDEX-OLD	\
@@ -3069,6 +3102,9 @@
 		rm ${BDHASH}-install
 	fi
 
+	# Make sure the system is configured correctly
+	install_verify_system || return 1
+
 	# Make sure we have all the files we should have
 	install_verify ${BDHASH}-rollback/INDEX-NEW	\
 	    ${BDHASH}-rollback/INDEX-OLD || return 1