prefixed with /sys generally special.
http://lists.freedesktop.org/archives/systemd-devel/2015-June/032962.html
-* Add PassEnvironment= setting to service units, to import select env vars from PID 1 into the service env block
-
* nspawn: fix logic always print a final newline on output.
https://github.com/systemd/systemd/pull/272#issuecomment-113153176