As many know, in Unity has incorporated its own application for lock screen or session as part of the process of improving its interface, as we already showed you in this article.
However, if you liked it more LightDM, With the help of Webupd8 We get a tip that will allow us to switch between both lock screens without any problem.
First we install the package CompizConfig Settings Manager:
sudo apt-get install compizconfig-settings-manager
Then we open CompizConfig Settings Manager » Ubuntu Unity Plugin » General we look in Lockscreen and there we can select what we want to use to lock the screen, as we can see in the following image.
No reboot is required for the changes to take effect.