Ubuntu 12.04

vi /etc/lightdm/lightdm.conf

添加：    allow-guest=false

           greeter-show-remote-login=false

Ubuntu 13.10

vi /etc/lightdm/lightdm.conf.d/50-guest-wrapper.conf

添加：allow-guest=false

Ubunt 14.04

/usr/share/lightdm/lightdm.conf/50-guest-wrapper.conf

添加：allow-guest=false

.

vim /etc/lightdm/lightdm.conf.d/50-greeter-wrapper.conf

添加： greeter-show-remote-login=false

最后重启下lightdm

sudo restart lightdm

或者

sudo apt-get remove gdm-guest-session