how to use ifplugd in Linux to execute a command or script when a NIC cable is unplugged or plugged in

It is fairly simple to use once you know how to use it.  However, the tricky thing is that by default it doesn't seem to be active or listen on any interface on manually specified.

How To Install ifplugd

First we install ifplugd

sudo apt install ifplugd

Let's enable it on our desired device(s)

vi /etc/default/ifplugd

set this line as so:

INTERFACES="enp0s8"
 

*Obviously change enp0s8 to the name of the NIC you want ifplugd to be active on, you can also enable it on multiple NICs by specifying a space. eg:

INTERFACES="eth0 eth1"

Let's create a sample script at first which is always placed in /etc/ifplugd/action.d/


touch /etc/ifplugd/action.d/yourscript.sh
chmod +x /etc/ifplugd/action.d/yourscript.sh

 

Remove /etc/ifplugd/action.d/ifupdown

I find this script can break other things you are trying to do so I recommend moving or removing it.  A good example is that it ended up interferring with my script below, where to make a NIC work it had to be brought up and down.  But then the ifupdown script would run and bring the NIC up again or down again.

So use the command below to move ifupdown into /etc/ifplugd so it doesn't get executed but you could always put it back into action.d if you wanted it again.

sudo mv /etc/ifplugd/action.d/ifupdown /etc/ifplugd/

An example of what yourscript.sh can be

In Unix/Linux there are often weird situations or even bugs in NICs that prevent them from working properly.  I have encountered some NICs that give you an uplink light and also show in ethttool that a 1gbit link is established.

Even ethttool looks good:

Settings for enp1s0:
    Supported ports: [ TP ]
    Supported link modes:   10baseT/Half 10baseT/Full
                            100baseT/Half 100baseT/Full
                            1000baseT/Full
    Supported pause frame use: No
    Supports auto-negotiation: Yes
    Advertised link modes:  10baseT/Half 10baseT/Full
                            100baseT/Half 100baseT/Full
                            1000baseT/Full
    Advertised pause frame use: Symmetric Receive-only
    Advertised auto-negotiation: Yes
    Speed: 1000Mb/s
    Duplex: Full
    Port: Twisted Pair
    PHYAD: 0
    Transceiver: internal
    Auto-negotiation: on
    MDI-X: Unknown
Cannot get wake-on-lan settings: Operation not permitted
    Current message level: 0x00000033 (51)
                   drv probe ifdown ifup
    Link detected: yes

However it is often the case that an ifdown and ifup is required to make the NIC work even though it is already configured with an IP (due to a driver bug especially in some NVIDIA based NICs):

Here is a script "yourscript.sh" that fixes that:

#!/bin/bash

#echo "in ifplugd" >> /tmp/ifplugd.txt
if [ "$2" == "up" ]; then
 /sbin/ifdown $1
 /sbin/ifup $1
 echo "executing state $2 ifdown ifup on :: $1 :: `date`" >> /tmp/ifplugdlog.txt
fi

 

 


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