# Ubuntu – How to bring up a network interface only if it is physically present in Ubuntu 14.04

12.0414.04bootnetworkingwireless

This is a follow-up on my old question:

What would be the best way to make kernel bring a network interface up
only if it is physically plugged in? So, if it doesn't exist, just
move on with initializing other interfaces (if any) and continue to
the login screen, without "waiting for network configuration" delay.

The solution then came up with then was the following in etc/network/interfaces, it used to work in 12.04:

auto wlan9
iface wlan9 inet manual
wpa-ssid MYSSD
wpa-psk MYKEY
wpa-proto RSN
wpa-pairwise CCMP
wpa-group CCMP
wireless-power off
pre-up if [ -f /sys/class/net/wlan9/operstate ]; then ifconfig wlan9 up; fi
up if [ -f /sys/class/net/wlan9/operstate ]; then dhclient wlan9; fi


Unfortunately, it stopped working once I upgraded to 14.04 Trusty Tahr. If the interface is physically absent (i.e. the USB WiFi card unplugged), I again experience the 2 minutes "waiting for network configuration" delay.

How can I get the same logic working in 14.04?

start on net-device-added INTERFACE=wlan9