+grub-install complains about /sbin/grub-install and/or xfs_freeze?!
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The following message:
+
+ You shouldn't call /sbin/grub-install. Please call /usr/sbin/grub-install instead!
+ xfs_freeze: specified file ["/tmp/tmpqaBK6z/boot/grub"] is not on an XFS filesystem
+
+... is "normal". grub-install sends those messages to stderr. To avoid hiding any
+possible real error messages grml2usb doesn't ignore those messages.
+