Ubuntu: Missing network interface and no UI
Solution 1:
To show all physical interfaces (in any state):
ip link show
To specifically show eth0:
ip link show eth0
This might show:
2: eth0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast state DOWN mode DEFAULT group default qlen 1000
link/ether 3c:97:0e:bb:8e:a8 brd ff:ff:ff:ff:ff:ff
Note that it's down.
To configure the interface for DHCP and bring it up:
dhclient eth0
ip link set eth0 up