''/etc/systemd/system/porridged.service'':

  [Unit]
  Description=Porridge Daemon
  Wants=network-online.target
  After=network.target network-online.target local-fs.target
  
  [Service]
  User=slack
  Group=slack
  WorkingDirectory=/home/slack/porridge/daemon
  Restart=always
  ExecStart=/home/slack/.rvm/wrappers/ruby-3.0.0/ruby /home/slack/porridge/daemon/bin/porridged
  
  [Install]
  WantedBy=network-online.target

[[https://unix.stackexchange.com/questions/271541/enabling-linked-unit-files-in-systemd|Then]]

  systemctl enable /home/slack/appname/appname.service
  service appname start

Check it is running with

  service appname status

If it has failed to run, start looking in ''/var/log/syslog''.