board/czechlight/beaglebone/overlay/usr/lib/systemd/system/save-machineid-to-uboot.service

[Unit]
Description=Save the machine-id into U-Boot environment if not set

[Service]
Type=oneshot
ExecStart=/bin/sh -c 'fw_printenv machineid &>/dev/null || fw_setenv machineid $(cat /etc/machine-id)'