Hmm.. When suspending my computer through inactivity, I'm prompted for password. Same thing when suspending through the Suspend item in the System meny. So I can't reproduce the issue after all.
One question, @Hadrien, is if your computer successfully entered into suspend mode. Can you please check what happens if you run the command: sudo systemctl suspend ** Changed in: lightdm (Ubuntu) Importance: High => Undecided ** Changed in: lightdm (Ubuntu) Status: Confirmed => Incomplete -- You received this bug notification because you are a member of Desktop Packages, which is subscribed to lightdm in Ubuntu. https://bugs.launchpad.net/bugs/1633751 Title: No login prompt when waking up the computer from suspend Status in lightdm package in Ubuntu: Incomplete Bug description: Ubuntu 16.10 x64. * I let my computer go to sleep. * Several hours later I wake it up. Expected result: the lock screen is displayed, waiting for me to input my password. Actual result: I am directly back to my desktop. I verified that the option to ask for my password at wake up is correctly checked. ProblemType: Bug DistroRelease: Ubuntu 16.10 Package: lightdm 1.19.5-0ubuntu1 ProcVersionSignature: Ubuntu 4.8.0-22.24-generic 4.8.0 Uname: Linux 4.8.0-22-generic x86_64 ApportVersion: 2.20.3-0ubuntu8 Architecture: amd64 CurrentDesktop: Unity Date: Sat Oct 15 18:34:14 2016 EcryptfsInUse: Yes InstallationDate: Installed on 2016-10-14 (0 days ago) InstallationMedia: Ubuntu 16.10 "Yakkety Yak" - Release amd64 (20161012.2) SourcePackage: lightdm UpgradeStatus: No upgrade log present (probably fresh install) To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/lightdm/+bug/1633751/+subscriptions -- Mailing list: https://launchpad.net/~desktop-packages Post to : desktop-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~desktop-packages More help : https://help.launchpad.net/ListHelp