thats work very well,
I read in this post: How To Install LightDM 1.7.0 On Ubuntu 13.10/13.04/12.10 And Linux Mint 16/15/14 and I ran:
sudo add-apt-repository ppa:lightdm-gtk-greeter-team/stable
sudo apt-get update
sudo apt-get install lightdm-gtk-greeter
but I disliked it, so I can't solve to my display manager default for Ubuntu, and after I did this:
Open lightdm.conf for editing in nano text editor:
sudo nano /etc/lightdm/lightdm.conf
You must have the following settings under [SeatDefaults]:
user-session=ubuntu
greeter-session=unity-greeter
Save and reboot.
It's great, this works. Thanks for your support.