Just as a side note, you should ignore those permissions errors. I don't know what's up with that package, but 777 is a terrible idea in general, let alone on directories like /etc and /usr... "Unsupported service manager" is the real issue.
There are two systemd service files included with the package, but only "surfsharkd.service" is enabled when installed.
snippet from the post-install script shipped with the .deb package, this is where your error is coming from as well as where it tries to enable the systemd unit
case "$(ps -p 1 --no-headers -o '%c' | tr -d '\n')" in
systemd)
systemctl daemon-reload || true
systemctl enable --global surfsharkd.service || true
;;
init)
update-rc.d surfshark defaults || true
update-rc.d surfshark2 defaults || true
/etc/init.d/surfshark restart || true
/etc/init.d/surfshark2 restart || true
;;
*)
echo "Unsupported service manager"
;;
esac
surfsharkd.service
[Unit]
Description=Surfshark Daemon
[Service]
ExecStart=/opt/Surfshark/resources/dist/resources/surfsharkd.js
Restart=on-failure
RestartSec=5
IPAddressDeny=any
RestrictRealtime=true
ProtectKernelTunables=true
ProtectSystem=full
RestrictSUIDSGID=true
[Install]
WantedBy=default.target
surfsharkd2.service
[Unit]
Description=Surfshark Daemon2
[Service]
ExecStart=/opt/Surfshark/resources/dist/resources/surfsharkd2.js
Restart=on-failure
RestartSec=5
IPAddressDeny=any
RestrictRealtime=true
ProtectKernelTunables=true
ProtectSystem=full
RestrictSUIDSGID=true
[Install]
WantedBy=default.target
If you want to take a shot at writing some service files for your preferred init then like @Hitman said that's where I'd start You could also try looking at the scripts that are installed to /etc/init.d, but if you're coming from systemd it might be easier to work from those services.