Answer by heemayl for Listing network hardware - why does Ubuntu sometimes hide eth0 until it is connected?

ifconfig by default shows only the interfaces that are Up. To see all interfaces, including the down one(s):

ifconfig -a

Note that, in GNU/Linux ifconfig (comes with net-tools) is deprecated in favor of newer ip (comes with iptoute2). With ip you can do:

ip addr show

Shorthand:

ip a

Check man ip to get more idea.