Oh, Ubuntu overrides the default shortcut to Ctrl+Alt+L (and Ubuntu GNOME overrode that back to Super+L)
https://bazaar.launchpad.net/~ubuntu-desktop/+junk/ubuntu- settings/view/head:/debian/ubuntu-settings.gsettings-override#L105 org.gnome.settings-daemon.plugins.media-keys screensaver See also LP: #830709 -- You received this bug notification because you are a member of Desktop Packages, which is subscribed to gnome-settings-daemon in Ubuntu. https://bugs.launchpad.net/bugs/1389650 Title: Ctrl+Alt+L fails to lock the screen in the default setup of Gnome 3 (gnome shell) Status in GNOME Settings Daemon: Confirmed Status in gnome-settings-daemon package in Ubuntu: Triaged Status in gnome-shell package in Ubuntu: Triaged Bug description: Ctrl+Alt+L fails to lock the screen in the default setup of Ubuntu 14.10 + Gnome 3 (gnome shell). All packages are up to date and I verified that Ctrl+Alt+L is indeed the shortcut to lock the screen. What helped was adding gnome-screensaver to the startup programs (was installed but wasn't started by default) as mentioned here: http://askubuntu.com/a/542391 To manage notifications about this bug go to: https://bugs.launchpad.net/gnome-settings-daemon/+bug/1389650/+subscriptions -- Mailing list: https://launchpad.net/~desktop-packages Post to : [email protected] Unsubscribe : https://launchpad.net/~desktop-packages More help : https://help.launchpad.net/ListHelp

