/usr/ is in gnome-session-flashback 1:3.28.0-1ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/
/usr/lib/gnome-flashback/
/usr/lib/gnome-flashback/gnome-flashback-compiz
/usr/lib/gnome-flashback/gnome-flashback-metacity
/usr/lib/systemd/
/usr/lib/systemd/user/
/usr/lib/systemd/user/gnome-session-flashback.target
/usr/share/
/usr/share/doc/
/usr/share/doc/gnome-session-flashback/
/usr/share/doc/gnome-session-flashback/copyright
/usr/share/gnome-session/
/usr/share/gnome-session/sessions/
/usr/share/gnome-session/sessions/gnome-flashback-compiz.session
/usr/share/gnome-session/sessions/gnome-flashback-metacity.session
/usr/share/xsessions/
/usr/share/xsessions/gnome-flashback-compiz.desktop
/usr/share/xsessions/gnome-flashback-metacity.desktop
/usr/share/doc/gnome-session-flashback/changelog.Debian.gz