I installed retropie on dietpi by Fourdee instruction.
https://github.com/MichaIng/DietPi/issues/1653
Thanks Fourdee & dietpi administrators for making a wonderful platform
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#Autostart RetroPie on boot
echo 3 > /DietPi/dietpi/.dietpi-autostart_index
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now retro pie autostart whenever my system reboot, I want to edit this way, I want my raspberry work as light as possible as server for other applications,. Please tell me the way if I want to initiate retropie I have to give some command through putty(other computer) to that machine & retropie will start & if system reboot, retropie component not auto start so that my server will stay cool with less active program. We use retropie once a month so it is not worth to run that in headless applications