I want to logout without rebooting the computer, but in 17.10 there is no option to logout in the top-right corner
There is only a button to lock the screen, and a button to restart or shutdown.
Click on your username in the top-right corner, there should be a logout option.
Alternatively, click on "Activities" (or press super) and search for "log out" (or the equivalent word in your system language, e.g. "abmelden" in German). A "Log out" icon should appear which should log you out.
Super
-Key and enter "abmelden" – rubo77 Feb 15 '18 at 17:20