====== Enable /etc/rc.local in Debian =======

Create a file ''/etc/systemd/system/rc-local.service'' and place the following contents in it:

  [Unit]
   Description=/etc/rc.local Compatibility
   ConditionPathExists=/etc/rc.local
  
  [Service]
   Type=forking
   ExecStart=/etc/rc.local start
   TimeoutSec=0
   StandardOutput=tty
   RemainAfterExit=yes
   SysVStartPriority=99
  
  [Install]
   WantedBy=multi-user.target
   
Save the file and make it executable:

  sudo chmod a+x /etc/systemd/system/rc-local.service
  
Create a file ''/etc/rc.local'' with this command:

  printf '%s\n' '#!/bin/bash' 'exit 0' | sudo tee -a /etc/rc.local
  
Make it executable:

  sudo chmod a+x /etc/rc.local
  
Finally, enable and start the newly created service with this command

  sudo systemctl enable --now rc-local