Script not working fully under systemd

Question

I have a python script to switch light/dark mode.

At the end there's this line:

process = subprocess.Popen(binDir + "/polybar.sh")

That script it points to is this:

#!/bin/env bash

# Terminate already running bar instances
killall -q polybar
polybar >/dev/null 2>/dev/null

If I execute the light/dark script from terminal it works perfectly, polybar gets killed and then relaunched.

However, I want a service to automatically switch depending on the time of the day, so I made some systemd timers. The light/dark script gets executed, most of the stuff in it works, but this in particular doesn't, it just kills polybar and it doesn't launch again. The systemd service is a user service.

I don't know how to troubleshoot this, systemctl status is not providing any info.

Why would a script work fine when launched from terminal, but not from systemd?

Here is the service file:

[Unit]
Type=simple
Description=dark mode
Environment="PATH=/home/{{ user }}/.local/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/home/{{ user }}/bin"
WorkingDirectory=/home/{{ user }}/bin

[Service]
ExecStartPre=/usr/bin/brightnessctl s 200
ExecStart=/usr/bin/python /home/ger/bin/nutra.py dark

And the timer:

[Unit]
Description=Turn screen dark/light at certain times

[Timer]
OnCalendar=*-*-* 18:13:00
Persistent=true


[Install]
WantedBy=timers.target

Answer 1

Jobs run through cron, or startup scripts, or systemd scripts, aren't run in the same runtime environment that you have on your desktop. Startup scripts are run as root. None of your PATH changes, or other environment variable settings from ~/.bashrc are automatically propagated to your cron job. For example, there's no $DISPLAY, so GUI programs need special treatment (read man xhost).

One can set environment variables for all one's cron jobs in the crontab file Read man 5 crontab.

Look at the results of echo "=== id ===";id;echo "=== set ===";set;echo "=== env ===";env | sort;echo "=== alias ===";alias in each of your environments.
An easy way is to store the commands in a bash script, and execute it from your terminal session, saving the output, then, execute the script from the "other" environment, saving the output. Compare the saved outputs using diff.

echo "=== id ===";id
echo "=== set ===";set
echo "=== env ===";env | sort
echo "=== alias ===";alias`