How to detect the physical connected state of a network cable/connector?
You want to look at the nodes in
/sys/class/net/
I experimented with mine:
Wire Plugged in:
eth0/carrier:1
eth0/operstate:unknown
Wire Removed:
eth0/carrier:0
eth0/operstate:down
Wire Plugged in Again:
eth0/carrier:1
eth0/operstate:up
Side Trick: harvesting all properties at once the easy way:
grep "" eth0/*
This forms a nice list of key:value
pairs.
You can use ethtool:
$ sudo ethtool eth0
Settings for eth0:
Supported ports: [ TP ]
Supported link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Full
Supports auto-negotiation: Yes
Advertised link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Full
Advertised auto-negotiation: Yes
Speed: 1000Mb/s
Duplex: Full
Port: Twisted Pair
PHYAD: 0
Transceiver: internal
Auto-negotiation: on
Supports Wake-on: umbg
Wake-on: g
Current message level: 0x00000007 (7)
Link detected: yes
To only get the Link status you can use grep:
$ sudo ethtool eth0 | grep Link
Link detected: yes
Use 'ip monitor' to get REAL TIME link state changes.