--- /dev/null
+#!/bin/bash -x
+
+set -eE -o pipefail
+trap 'echo "$0:$LINENO:error: \"$BASH_COMMAND\" returned $?" >&2' ERR
+
+if [[ $EUID != 0 ]]; then
+ echo "$0: error: expected to be root."
+ exit 1
+fi
+
+cat >$FAI_ROOT/etc/grub.d/40_custom <<EOF
+#!/bin/sh
+exec tail -n +3 \$0
+# This file provides an easy way to add custom menu entries. Simply type the
+# menu entries you want to add after this comment. Be careful not to change
+# the 'exec tail' line above.
+
+# https://www.coreboot.org/Serial_console # tty
+# but removed unneeded stuff
+
+serial --speed=$speed
+terminal_input --append serial
+terminal_output --append serial
+EOF