[Service]
# may need `sudo systemctl daemon-reload` afterward
# need a line of `ExecStart=` to clear the list first, 
# more about drop-in dir see `man systemd.unit`, more about ExecStart see `man systemd.service`
# https://wiki.archlinux.org/title/Systemd#Drop-in_files
# https://wiki.archlinux.org/title/Systemd#Examples
ExecStart=
ExecStart=/usr/bin/paccache -rk0