Raspberry Pi USB Joystick Not Working Immediately After Bootup

Question

I am using a Raspberry Pi4 with a USB Logitech Extreme 3D joystick. I have a Python 3 application using the evdev library to read the joystick which works fantastic, however, when I first boot the pi, the program cannot access the joystick until I disconnect and reconnect it. I have a udev rule which creates a symlink to the joystick.

I have verified that the joystick is being recognized and the symlink is being created upon bootup.

I also installed PyUSB to do some testing. If I boot the pi and go into a terminal, run python 3 and try to configure the joystick using PyUSB, it gives me the following error.

import usb.core
import usb.util
dev = usb.core.find(idVendor=0x046d, idProduct=0xc215)
print(dev)                #This outputs the correct information, indicating I am finding it
dev.set_configuration()   #This throws the following error

usb.core.USBError: [Error 16] Resource busy

This makes me think something else is binding to the joystick during boot before my application can grab it. I'm not sure how to troubleshoot this. Can anyone offer suggestions?

I have been searching for answers but can't find a solution to this exact problem.

Any help is much appreciated

**UPDATE 1 ** with info from a comment:
I have a bash script that is called from /etc/X11/xinit/xinitrc when the X system is started and I run startx from systemd at startup. The systemd waits for the device to be present and sets the environment XAUTHORITY=/home/pi/.Xauthority which is the user I am running the script under.

**UPDATE 2 ** After trying suggested answer from @Ingo, this is my systemd file:

[Unit]
Description=Start-Program
After=graphical.target

[Service]
User=pi
Environment=DISPLAY=:0.0
Environment=XAUTHORITY=/home/pi/.Xauthority
ExecStart=/home/pi/myprog/program-start.sh

[Install]
WantedBy=graphical.target

Answer 1

Starting a script with dependencies is one of the main functions of systemd. Seems you try to do it past systemd. It is very likely that this is confusing it. You should just use a Unit file and nothing else. All other things are managed very good by systemd.

Here is a simple suggestion. it may need some additional settings, if it doesn't run on the first try. We can look at it then. Create a new service with:

rpi ~$ sudo systemctl edit --force --full your-script.service

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

[Unit]
Description=Your bash script
After=graphical.target

[Service]
User=pi
Environment=XAUTHORITY=/home/pi/.Xauthority
#ExecStartPre=/usr/bin/printenv
ExecStart=/full/path/to/your-script.sh

[Install]
WantedBy=graphical.target

To get the environment on runtime, uncomment ExecStartPre=... You will find its output with journalctl -b. Enable the service:

rpi ~$ sudo systemctl enable your-script.service

and reboot. Check it with:

rpi ~$ systemctl status your-script.service

If you are interested what systemd all is doing in the background you can show it with:

rpi ~$ systemctl show your-script.service

This may give an idea that it's the best to let only systemd do the work.