Ubuntu: wait for network link up and execute a bash command

Question

In Ubuntu (the latest distro is fine), I want to reboot a router and inside a bash script I\'d like to have a command that waits for the network link to be up again and, whe

Answer 1

The event listener I suggested:

inotifywait -e modify /sys/class/net/eth0/carrier; echo 'Change detected'

When you plug or unplug network cable, it will trigger echo 'Change detected', of course it could trigger just about anything.

And this will run as one off, but I take you know how to make a daemon out of it, if not it will be a good exercise to learn :)

Answer 2

If you want a command to check if the link is up or down use ip :

ip addr show eth0 | grep -Po "(?<=state ).*?(?=\s)"
DOWN

ip addr show wlan0 | grep -Po "(?<=state ).*?(?=\s)"
UP

Answer 3

You can check link is up/down by /sys/class/net/eth0/carrier file

cat /sys/class/net/eth0/carrier

if output is 1 then ethernet cable is plugged in and link is up.

if output is 0 then ethernet cable is removed and link is down.

Note:if you have interface other then eth0 then replace interface like eth2/eth3 in place of eth0