remotely log out of (graphical) gnome session
Solution 1:
After logging in with ssh, run:
env DISPLAY=:0.0 gnome-session-quit --logout
This will force a logout on the remote machine just as if you had logged out from the menu (but without prompting). You may need to run gnome-session-quit with --force-logout if there's an application with, for example, unsaved work, that would otherwise prevent a clean logout.
If you use a very old version (<2011) of GNOME, then you need to
env DISPLAY=:0.0 gnome-session-save --logout
... because gnome-session-save was renamed to gnome-session-quit in 2011.
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