ConsoleKit2 is a framework for defining and tracking users, login
sessions, and seats. It allows multiple users to be logged in at the
same time and share hardware for their graphical session. ConsoleKit2
will keep track of those resources and whichever session is active
will have use of the hardware at that time.

What is a seat?
===============
A seat is a collection of sessions and a set of hardware (usually at
least a keyboard and mouse). Only one session may be active on a
seat at a time.

What is a session?
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A session is a collection of all processes that originate from a single
common ancestor and retain knowledge of a secret. As an implementation
detail, this secret may be stored in the process environment by the
login manager under the name XDG_SESSION_COOKIE.