$ sudo apt-get update
$ sudo apt-get install lxsession-logout 

lxsession-logout is installed in your system.

Make ensure the lxsession-logout package were installed using the commands given below,

$ sudo dpkg-query -l | grep lxsession-logout *

You will get with lxsession-logout package name, version, architecture and description in a table

lxsession-logout package basic information: