In Fedora 20 , GNOME3 has changed how the user menu works. One change is that there is no Logout option in your menu options.
Basically, this change is based on this:
if you only have one user set up on a system, and only have one Desktop environment installed (i.e. just GNOME) then the logout option is not shown.
There are three ways to solve this trouble.
1.You can install another desktop environment(KDE i.e.);
2.You can create a new user, and reboot the OS;
3.Use the dconf to show the Logout option in Menu,using the command below:
dconf write /org/gnome/shell/always-show-log-out true
, and the Logout option will appear in your menu immediately.