How to run user program when the Raspberry Pi boots.

To run a user program on Raspberry Pi at boot, you can follow these steps:

Create a script for your program in the "/etc/init.d/" directory.
Make the script executable by running sudo chmod +x /etc/init.d/yourscript.
Update the system boot sequence by running sudo update-rc.d yourscript defaults.
Reboot the Raspberry Pi to confirm the script runs at boot.

Alternatively, you can also add the command to run your program to the "/etc/rc.local" file, above the "exit 0" line. This file is executed at boot before the graphical user interface starts.