/usr/share/gnome-session/sessions/gnome-classic.session is in gnome-session-fallback 3.2.1-0ubuntu8.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 | [GNOME Session]
Name=GNOME Classic
RequiredComponents=gnome-panel;gnome-settings-daemon;
RequiredProviders=windowmanager;
DefaultProvider-windowmanager=gnome-wm
DefaultProvider-notifications=notify-osd
IsRunnableHelper=/usr/lib/gnome-session/gnome-session-check-accelerated
FallbackSession=gnome-fallback
DesktopName=GNOME
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