sudo nano /etc/rc.local

• Add your lines before the exit 0
• You may need to cd to the directory  first  (it won’t hurt to have this, but isn’t strictly required)
• If your script runs in the background, put an ampersand,  ‘&’ at the end of the line calling your executable, or you will not be able to get control of your pi easily
• If your script terminates, you don’t have to use the ‘&’

e.g.,

cd /home/pi/mysubdirectory
python3 /home/pi/mysubdirectory/myexecutable.py &

Reboot, then run ps aux | grep myexecutable.py to see if it worked (see Kill a Process for details).

If it doesn’t work:

• Be sure you put your lines BEFORE exit 0
• Execute the same line from your command line.  Chances are your program has a bug which you will see in the terminal window.
• Did you reboot?