I know that I can poll the link state via the SIOCETHTOOL/ETHTOOL_GLINK ioctl but this would require to endlessly request the state. The same goes for parsing /var/log/messages. So my questin is, is there any way under Linux to wait on a state change of the ethernet cable from userspace?
Wait for ethernet cable plug-in/plug-out event under Linux?
linux;ethernet
How about ifplugd?ifplugd is a Linux daemon which will automatically configure your ethernet device when a cable is plugged in and automatically unconfigure it if the cable is pulled. This is useful on laptops with onboard network adapters, since it will only configure the interface when a cable is really connected.(There is also netplugd, but it was discontinued.)