One-liner installation with defaults (Bullseye and newer):

curl https://raw.githubusercontent.com/hipi-io/ups-hat/main/systemd/install-UPS-systemd-Bullseye.sh | bash

One-liner installation with defaults (Buster and older):

curl https://raw.githubusercontent.com/hipi-io/ups-hat/main/systemd/install-UPS-systemd-Buster.sh | bash

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Manual installation (adapt to the OS you are using)

change the permissions for the script

sudo chmod +x ups.sh

copy the script to the init.d directory to run the script on startup

sudo cp ups.sh /etc/init.d/

update the rc file

sudo update-rc.d ups.sh defaults