systemd

Systemd can be scary. Full documentation here.

quick reference

Just need something quick. Create /etc/systemd/system/my-service.service file:

[Unit]
Description=<description about this service>

[Service]
User=<user e.g. root>
WorkingDirectory=<directory_of_script e.g. /root>
ExecStart=<script which needs to be executed>
Type=notify
Restart=always

[Install]
WantedBy=default.target

alternative

Use cron with @reboot tag to run your script at boot!