Delete MATE Enviroment on Ubuntu

To remove MATE DE completely you can use the following commands:

1. Parse dpkg --list output to get all mentions of MATE and then remove packages with MATE in its description:
   

   sudo apt-get purge $(dpkg --list | grep MATE | awk '{print $2}')
   

2. Remove some leftover packages (including Plymouth boot screen) manually with commands below:
   

   sudo apt-get purge libmate-sensors-applet-plugin0
   sudo apt-get purge libmateweather-common libmateweather1:amd64
   sudo apt-get purge mate-accessibility-profiles
   sudo apt-get purge mate-notification-daemon
   sudo apt-get purge mate-notification-daemon-common
   sudo apt-get purge plymouth-theme-ubuntu-mate-logo 
   sudo apt-get purge plymouth-theme-ubuntu-mate-text
   

   (they are presented by single lines to to be more fail-proof - to avoid the situation if one of them are not installed)
3. Install system components back if there were removed with previous commands:
   

   sudo apt-get install ubuntu-release-upgrader-gtk update-manager update-notifier
   

4. And then finally reconfigure your login screen with
   

   sudo dpkg-configure lightdm # for LightDM
   sudo dpkg-configure gdm3 # for GDM3