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How to bring up a network interface only if it is physically present

rated 0 times [ 3] [ 0] / answers: 1 / hits: 23595 / 2 Years ago, wed, april 20, 2022, 2:04:52

Running Ubuntu Server 12.04 (no GUI). 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.

E.g, I have a wireless USB key wlan9 (in /etc/network/interfaces):

auto wlan9

iface wlan9 inet dhcp

        wpa-ssid myssd

        wpa-psk mykey

        wpa-proto RSN

        wpa-pairwise CCMP

        wpa-group CCMP

I tried allow-hotplug instead of auto, in which case the interface doesn't get initialized automatically during the boot, and I have to do it manually with ifup wlan9. This is not exactly what I'm looking for.

Thank you.

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poefor

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2 Years ago

answered 2 Years ago biryanrownies · Accepted Answer

I've come up with the following solution which doesn't depend on any extra packages:

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

While it may not be elegant, it does what I want: skips wlan9 initialization without boot delay if the wireless dongle is not plugged in, otherwise brings it up.