#5 error if ethtool is noot present

[Davy]

if ethtool is not install then config if will produce an error
this could be corrected by sending stderr to /dev/null

[Lars]

The issue is fixed now in muninlite's new repository at github:
https://github.com/munin-monitoring/muninlite/commit/44d1c8dc3aef0186bf6934fd1307133703f7916f