Systemd doesn’t stop the service when the device is removed

systemdudev

I've a udev rule:

ACTION=="add", SUBSYSTEM=="usb", ATTR{idVendor}=="1a86", ATTR{idProduct}=="7523", TAG+="systemd", ENV{SYSTEMD_WANTS}+="klipper.service"

Original service is a sysv file:

pi@octopi:/etc/udev/rules.d $ sudo service klipper status
● klipper.service - Modiffied Klipper systemd file
   Loaded: loaded (/etc/init.d/klipper; generated; vendor preset: enabled)
  Drop-In: /etc/systemd/system/klipper.service.d
           └─override.conf

So i override it using sudo systemctl edit klipper.service then I enter this in the override file:

[Unit]
Description=Modiffied Klipper systemd file
StopWhenUnneeded=yes

Now, when i unplug the device the service still stays "active" and doesn't stop.

This is what they suggest doing:
https://bugzilla.redhat.com/show_bug.cgi?id=871074

I want this service to stop when the device is removed.

Here's the content of sysv init file

#!/bin/sh
# System startup script for Klipper 3d-printer host code

### BEGIN INIT INFO
# Provides:          klipper
# Required-Start:    $local_fs
# Required-Stop:
# Default-Start:     2 3 4 5
# Default-Stop:      0 1 6
# Short-Description: Klipper daemon
# Description:       Starts the Klipper daemon.
### END INIT INFO

PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
DESC="klipper daemon"
NAME="klipper"
DEFAULTS_FILE=/etc/default/klipper
PIDFILE=/var/run/klipper.pid

. /lib/lsb/init-functions

# Read defaults file
[ -r $DEFAULTS_FILE ] && . $DEFAULTS_FILE

case "$1" in
start)  log_daemon_msg "Starting klipper" $NAME
        start-stop-daemon --start --quiet --exec $KLIPPY_EXEC \
                          --background --pidfile $PIDFILE --make-pidfile \
                          --chuid $KLIPPY_USER --user $KLIPPY_USER \
                          -- $KLIPPY_ARGS
        log_end_msg $?
        ;;
stop)   log_daemon_msg "Stopping klipper" $NAME
        killproc -p $PIDFILE $KLIPPY_EXEC
        RETVAL=$?
        [ $RETVAL -eq 0 ] && [ -e "$PIDFILE" ] && rm -f $PIDFILE
        log_end_msg $RETVAL
        ;;
restart) log_daemon_msg "Restarting klipper" $NAME
        $0 stop
        $0 start
        ;;
reload|force-reload)
        log_daemon_msg "Reloading configuration not supported" $NAME
        log_end_msg 1
        ;;
status)
        status_of_proc -p $PIDFILE $KLIPPY_EXEC $NAME && exit 0 || exit $?
        ;;
*)      log_action_msg "Usage: /etc/init.d/klipper {start|stop|status|restart|reload|force-reload}"
        exit 2
        ;;
esac
exit 0

Best Answer

StopWhenUnneeded=true does work as desired. What doesn't work is deactivating the device.

You can verify this by doing systemctl status DEVICENAME.device with the device inserted and removed. I bet what you'll find is the device activates when the device is inserted, and stays activated after it's removed.

To find DEVICENAME, you can look for it in systemctl list-units --type=device. You can also add ENV{SYSTEMD_ALIAS}="..." to your udev rule to give your device a more predictable unit name. See man systemd.device.

The issue is documented in more detail at https://github.com/systemd/systemd/issues/7587. The problem is apparently the kernel events for the device removal are missing the tags to get them even routed to systemd so it knows to deactivate the device unit.

A workaround is to add a udev rule that adds the systemd tag. In your case, probably something like:

ACTION=="remove", SUBSYSTEM=="usb", ENV{PRODUCT}=="1a86/7523/*", TAG+="systemd"

With that in place, you should then be able to confirm that the device unit reflects the current plugged/unplugged state of the device, and then StopWhenUnneeded=true in the service unit will stop the service when the device is unplugged.

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