(RaspberryPi2)ubuntu@localhost:~$ grep systemd /etc/system-image/writable-paths  
# used by click-systemd
/var/lib/systemd/click                  auto                    persistent  transition  none
# used by snappy-systemd
/var/lib/systemd/snappy                 auto                    persistent  transition  none
/etc/systemd/system                     auto                    persistent  transition  none
/var/lib/systemd/random-seed            auto                    persistent  transition  none
(RaspberryPi2)ubuntu@localhost:~$