Linux Live

Often a just-installed Linux will have NetworkManager running, but not set up to handle the NIC.  This example is working on Debian Testing.  Here is a standard single-NIC /etc/network/interfaces:

 # This file describes the network interfaces available on your system
 # and how to activate them. For more information, see interfaces(5).

 # The loopback network interface
 auto lo
 iface lo inet loopback

 # The primary network interface
 iface eth0 inet dhcp
 auto eth0

 #iface eth1 inet dhcp
 #auto eth1

and here is the corresponding /etc/NetworkManager/nm-system-settings.conf :

 [main]
 plugins=ifupdown,keyfile

 [ifupdown]
 managed=true