I want to use Systemd (Systemctl) to launch a program immediately after Systemd is launched. Even before the device establishes an Internet connection or network. For reference this is a Raspberry Pi and I want to turn on the 16x2 LCD display with text as soon as possible after the Raspbian based OS has booted up. Thanks!
add the desired command/script to execute when the OS boots up by modifying the .xinitrc file.
Read more about modifying OS start functionality here.