Get event for NIC/ethernet card link status on linux

Question

Is there any API(or special file) on Linux that provides an event on the change in link status of an ethernet card without polling ? i.e. when you plug in/out the cable ?

Answer 1

You can get link up/down events via netlink. You would create a PF_NETLINK socket, bind to the RTMGRP_LINK group, and wait for RTM_NEWLINK/RTM_DELLINK messages. Link up events have IFF_RUNNING and IFF_LOWER_UP set in ifinfomsg.flags, while link down events have both flags cleared (funnily enough, I'm getting RTM_NEWLINK messages for both type of events).

Answer 2

If the contents of this file /sys/class/net/eth0/carrier are 1, then the interface eth0 has carrier.