my interfaces file
auto lo iface lo inet loopback
auto eth0 iface eth0 inet dhcp
networkmanager.conf
[main] plugins=ifupdown,keyfile
[ifupdown] managed=false
my interfaces file
auto lo
iface lo inet loopback
auto eth0
iface eth0 inet dhcp
networkmanager.conf
[main] ifupdown, keyfile
plugins=
[ifupdown]
managed=false