+=item FEBOOTSTRAP_KERNEL
+
+=item FEBOOTSTRAP_MODULES
+
+These two environment variables allow the kernel that libguestfs uses
+in the appliance to be selected. If C<$FEBOOTSTRAP_KERNEL> is not
+set, then the most recent host kernel is chosen. For more information
+about kernel selection, see L<febootstrap-supermin-helper(8)>. This
+feature is only available in febootstrap E<ge> 3.8.
+
+=item GUESTFISH_DISPLAY_IMAGE
+
+The C<display> command uses C<$GUESTFISH_DISPLAY_IMAGE> to
+display images. If not set, it uses L<display(1)>.
+