root 21:41:11 : ~ # systemctl disable serial-getty@ttymxc4.service
Failed to issue method call: Read-only file system
root 21:41:20 : ~ # rootfs.writable 
mounting rootfs writable
UBIFS: background thread "ubifs_bgt0_0" started, PID 809
root 21:41:24 : ~ # systemctl disable serial-getty@ttymxc4.service
rm '/etc/systemd/system/getty.target.wants/serial-getty@ttymxc4.service'
root 21:41:27 : ~ # systemctl stop serial-getty@ttymxc4.service