systemd service not executing the python script

Question

I was making a battery notifier script for my raspberry pi3. The script is executing when I do

/usr/bin/python /home/pi/Documents/shutdown.py

and showing the popup notifications.  However the service is not executing it or not showing the notification.  I can see the python process if I do sudo systemctl status battery-notifier.service.

battery-notifer.service

[Unit]
Description=Battery Notifier

[Service]
Type=simple
WorkingDirectory=/home/pi/Documents
ExecStart=/usr/bin/python /home/pi/Documents/shutdown.py

[Install]
WantedBy=multi-user.target

shutdown.py

import raspiupshat
import statistics
import subprocess
from time import sleep
raspiupshat.init()
while(True):
    voltagesList = []
    sleep(0.5)
    currentVoltage = raspiupshat.getv()
    voltagesList.append(currentVoltage)
    medianVoltage = statistics.median(voltagesList)
    if(medianVoltage>4):
        subprocess.Popen(["notify-send","Battery Full!"])

This is the status of the service when I do sudo systemctl status battery-notifier.service:

● battery-notifier.service - Battery Notifier
   Loaded: loaded (/lib/systemd/system/battery-notifier.service; enabled)
   Active: active (running) since Sat 2017-07-15 04:05:18 UTC; 48min ago
 Main PID: 28384 (python)
   CGroup: /system.slice/battery-notifier.service
           └─28384 /usr/bin/python /home/pi/Documents/shutdown.py

Jul 15 04:05:18 raspberrypi systemd[1]: Started Battery Notifier.

Answer 1

Edited to add: Your program tries to access the graphical desktop of a user (pi), however, it is itself executed by systemd. That is, it will run as root per default and not as the user pi. Moreover, there might not even be a graphical desktop yet at the time this is started.

Therefore, you could go several paths:

• Start the program not via systemd, but when the logged in user starts the graphical desktop. Therefore, you need to put the program start into the file ~/.xinitrc or ~/.xprofile. See the Arch Wiki on Autostart
• Add a line User=pi to your systemd service. This is the solution you mentioned in the comment to your original post
• systemd can be configure to be executed in a user-mode (as opposed to system mode) when the user logs in. You could let your service be started by that way. See the Arch Wiki on systemd/User

---

Original answer:

See this SO question. There is an env= parameter in the subprocess.Popen(.) function which can be used.

Alternatively, you could use the feature of sh that if you assign a variable immediately before a call, that variable is set (only) for that call:

myvar=world
# cannot use echo $myvar, because $myvar would be substituted before echo is launched
myvar=hello declare -x myvar 
echo $myvar

gives

declare -x myvar="hello"
world

Link to corresponding chapter in POSIX spec

So for you:

subprocess.call("DBUS_SESSION_BUS_ADDRESS=unix:abstract=/tmp/dbus-goOEk5dZcK,‌​guid=9c1f14175e6be09‌​92b16e5155969b46c notify-send 'Battery full!'",s‌​hell=True)

The call you mentioned in the comment to your question does not work because it leads to the following process

• subprocess.Popen('export DBUS_SESSION_BUS_ADRESS=..., shell = True)

  • Launch a shell

  • Set the environment variable DBUS_SESSION_BUS_ADRESS=... for this shell and all sub-shells (that's what export does).

    What it does NOT: Set the variable for all shells there are on the machine!

  • Close the shell. Now the value of DBUS_SESSION_BUS_ADRESS is lost again.
• subprocess.Popen(['notify-send',...], shell=True)
  • Launch a shell
  • The export call of the previous shell has no power here because these two shells are completely unrelated
  • Launch notify-send as in your original question

So the setting of the environment variable has no effect here.