Make ifplugd available with systemd

ifplugd is running as daemon so we have to use a systemd service to manage it. I will only use the daemon program /usr/sbin/ifplugd without the management scripts from Debian.

Tested with
Raspberry Pi OS 2020-12-02 based on Buster on a Raspberry Pi 4B updated at 2020-05-12.
Raspbian Stretch Lite 2019-04-08 updated at 2019-04-16.
Updates done with sudo apt update && sudo apt full-upgrade && sudo reboot.

Install ifplugd program

First we download the ifplugd package but don't install it, only extract the daemon program:

rpi ~$ apt download ifplugd rpi ~$ ar -p ifplugd_*_armhf.deb data.tar.xz | sudo tar -xJ -C / ./usr/sbin/ifplugd rpi ~$ rm ifplugd_*_armhf.deb rpi ~$ ifplugd --version # at the time testing this ifplugd 0.28 (SVN: 124) 

Create new service for the ifplugd program

We will not run ifplugd as classic daemon. Instead we run it as service and do not have to "daemonize" it. Look at the man page ⁽¹⁾ that we have to use option --no-daemon. Other options are used to disable functions that are managed by systemd now. Create the new service with:

rpi ~$ sudo -Es rpi ~# systemctl --full --force edit [email protected] 

In the empty editor insert these statements, save them and quit the editor:

[Unit] Description=Interface plug monitor (interface-specific version) Documentation=https://raspberrypi.stackexchange.com/a/96605/79866 After=sys-subsystem-net-devices-%i.device [Service] ExecStart=/usr/sbin/ifplugd --iface=%i --no-daemon --no-auto --no-syslog --no-beep --no-shutdown --run=/etc/ifplugs/ifplugs.action [Install] WantedBy=sys-subsystem-net-devices-%i.device 

Create Action Script

As described in the man page ⁽¹⁾ the service calls a script on every event up and down on an interface. Here I will use a template. Create this action script with your editor:

rpi ~# mkdir /etc/ifplugs rpi ~# editor /etc/ifplugs/ifplugs.action 

In the empty editor insert these statements, save them and quit the editor:

#!/bin/bash # redirect all output into a logfile for debug #exec 1>> /tmp/ifplugs-debug.log 2>&1 INTERFACE="$1" EVENT="$2" IPADDR='' get_ipaddr () { if [ "$EVENT" = "down" ]; then IPADDR=$(/sbin/ip -4 -br addr show $INTERFACE | /bin/grep -Po "\d+\.\d+\.\d+\.\d+") return 0 fi # check 10 times with 1 sec delay if ip address is available for ((i=10; i>0; i--)); do IPADDR=$(/sbin/ip -4 -br addr show $INTERFACE | /bin/grep -Po "\d+\.\d+\.\d+\.\d+") [ $? -eq 0 ] && break /bin/sleep 1 done } case "$INTERFACE" in eth0) case "$EVENT" in up) # do stuff on connect with interface get_ipaddr echo "$INTERFACE" up with ip address \""$IPADDR"\" ;; down) # do stuff on disconnect with interface get_ipaddr echo "$INTERFACE" down with ip address \""$IPADDR"\" ;; *) >&2 echo empty or undefined event for "$INTERFACE": \""$EVENT"\" exit 1 ;; esac ;; wlan0) case "$EVENT" in up) # do stuff on connect with interface get_ipaddr echo "$INTERFACE" up with ip address \""$IPADDR"\" ;; down) # do stuff on disconnect with interface get_ipaddr echo "$INTERFACE" down with ip address \""$IPADDR"\" ;; *) >&2 echo empty or undefined event for "$INTERFACE": \""$EVENT"\" exit 1 ;; esac ;; *) >&2 echo empty or unknown interface: \""$INTERFACE"\" exit 1 ;; esac 

Make it executable:

rpi ~# chmod +x /etc/ifplugs/ifplugs.action 

/usr/sbin/ifplugd needs an own instance for every interface. So we start them with the interface-specific version:

rpi ~# systemctl start [email protected] rpi ~# systemctl start [email protected] rpi ~# exit rpi ~$ 

If you want to start the ifplug.service on boot up, just enable it:

rpi ~$ sudo systemctl enable [email protected] rpi ~$ sudo systemctl enable [email protected] 

Now the actions up and down for each monitored interface are logged to the journal. Follow it with

rpi ~$ journalctl --follow # You may filter it with: rpi ~$ journalctl --follow | grep ifplugd 

You are free to modify /etc/ifplugs/ifplugs.action or create your own. If you want to monitor other interfaces then just use its interface names for the interface-specific services and in the action script instead of eth0 and wlan0 in this example.

References:
(1): man page ifplugd