LightDM screenshot, using the “Unity Greeter” frontend. Español: Captura de pantalla de LightDM, usando la interfaz «Unity Greeter». (Photo credit: Wikipedia)
Borrowing is a nasty habit. It is worse to borrow somebody’s laptop. In principle everybody tends to agree but in practice expediency over-rules the principle. So I have decided to disable Guest Login from my lap top and if somebody asks for it he will have to find his own way to login (i.e. by own usb). This is how I managed to disable the guest account in Precise Pangolin 12.04 LTS (lightDM log in).
Open Terminal and type:
sudo gedit /etc/lightdm/lightdm.conf
It will open text editor with lightdm.conf file with following entries:
[SeatDefaults] user-session=ubuntu greeter-session=unity-greeter
Add following line at the end:
allow-guest=false
And Save.
Before closing, make sure that final result should look like:
[SeatDefaults] user-session=ubuntu greeter-session=unity-greeter allow-guest=false
Close the editor. Close all Running programs and re-login by tying the following command in terminal:
sudo restart lightdm
It will ask your password and log-off real fast.
It would be back to login screen with guest account disabled.
P.S.: This worked on a clean install of Precise Pangolin 12.04 LTS (amd64). I am not sure that it will work on upgrade as earlier built may be using GDM. If you try, do it on your own risk, but do tell me the result.
© Sandeep Bhalla
Sandeep Bhalla's Blog 
Ultimately I had to remove it alltogether and I installed LinuxMint Maya (13.0).
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on the upgraded version from 11.10 to 12.04 LTS, sudo won’t open the file nor will it allow me to change the file directly in the directory without permission from root.. which i am.. weird.. even as root i cannot edit the file.. how retarted.. wish i would’ve stayed with 10.10..
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