you should see something like these in your vanilla rootfs...
############!/bin/sh
#[ "$(uci get rpcd.@rpcd[0].socket)" = "/var/run/ubus.sock" ] && {
# uci set rpcd.@rpcd[0].socket='/var/run/ubus/ubus.sock'
# uci commit rpcd
#
#}
#[ "$(uci -q get uhttpd.main.ubus_socket)" = "/var/run/ubus.sock" ] && {
# uci set uhttpd.main.ubus_socket='/var/run/ubus/ubus.sock'
# uci commit uhttpd
#
#}
fgrep -r ubus build_dir/*/root* | grep sock