eth up/down

Up another LAN interface if one is link down

#!/bin/bash

# Periodically check a interface for link up.

# If found the current interface link down,

# up another interface and down the current interface.

# It consume about 0.3% of CPU and 0.1% of Memory.

while :

do

if [[ $(ip link show | grep eth0 | cut -d ',' -f 3) = UP ]]

then

echo eth0 Up > /dev/null

else

        if [[ $(ip link show | grep eth1 | cut -d ',' -f 3) = UP ]]

        then

        echo eth1 already Up > /dev/null

        else

        /sbin/ifup eth1 &> /dev/null

        /sbin/ifdown eth0 &> /dev/null

        fi

fi

sleep 1

if [[ $(ip link show | grep eth1 | cut -d ',' -f 3) = UP ]]

then

echo eth1 Up > /dev/null

else

        if [[ $(ip link show | grep eth0 | cut -d ',' -f 3) = UP ]]

        then

        echo eth0 already Up > /dev/null

        else

        /sbin/ifup eth0 &> /dev/null

        /sbin/ifdown eth1 &> /dev/null

        fi

fi

sleep 1

done