FAQforge

Ubuntu’s login manager, lightdm, offers a guest login option by default.

Most of you won’t use it anyway, so why keep it at all? You can disable that entry in the lightdm configuration file, which is /etc/lightdm/lightdm.conf. Open it from a terminal using

sudo gedit /etc/lightdm/lightdm.conf

At the bottom of the file, insert following line:

allow-guest=false

Afterwards, restart your machine and the guest login option will be gone. To bring it back, just erase the line again or set it to true.