openwrt/target/linux/ar71xx/base-files/etc/uci-defaults/00_inittab-console-fixup

#!/bin/sh
#
# Copyright (C) 2011 OpenWrt.org
#

enable_console_login() {
	local cons=$1
	local initline="$cons::askfirst:/bin/ash --login"

	grep -qs "^$initline" /etc/inittab || {
		echo "$initline" >> /etc/inittab
		sync
		kill -HUP 1
	}
}

inittab_console_fixup() {
	for cons in ttyS0 ttyATH0; do
		grep -qs "console=$cons" /proc/cmdline && {
			enable_console_login $cons
		}
	done
}

inittab_console_fixup

exit 0