How to numlockx on ubuntu 18.04

1. Open terminal via Ctrl+Alt+T, then run command to get root privilege:

   sudo -i
   

2. Switch to user gdm in the terminal:

   su gdm -s /bin/bash
   

3. Finally set ‘Numlock on’ via gdm user:

   gsettings set org.gnome.settings-daemon.peripherals.keyboard numlock-state 'on'
   

Restart the computer and done

site:  https://askubuntu.com/questions/1028428/how-to-set-numlock-on-as-default-at-login-screen