Re: Detecting link up

[Stephen Hemminger]

Filipe Abrantes wrote:
> Hi all,
>
> I need to detect when an interface (wired ethernet) has link up/down. Is 
> there a system signal which is sent when this happens? What is the best 
> way to this programatically?
>
> Best Regards
>
> Filipe

The best way is to open a netlink socket and look for the mesaages about
link up/down there. Read iproute2 http://developer.osdl.org/dev/iproute2 
source for ip command (ipmonitor.c).

This works for almost all devices unlike ethtool and mii which only
work on a small subset of devices.
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