Got same issue after an upgrade from Ubuntu 14.04 to 16.04 and the following actions solved the problem :
sudo pam-auth-update --force sudo vi/etc/pam.d/lightdm => add following lines at the end : session required pam_loginuid.so session required pam_systemd.so sudo reboot -- You received this bug notification because you are a member of Ubuntu Touch seeded packages, which is subscribed to lightdm in Ubuntu. https://bugs.launchpad.net/bugs/1240336 Title: After release upgrade, the user looses permissions for several basic actions in the system Status in gdm package in Ubuntu: Triaged Status in lightdm package in Ubuntu: Triaged Status in lxdm package in Ubuntu: Triaged Status in policykit-desktop-privileges package in Ubuntu: Triaged Bug description: HOW TO REPRODUCE: - Upgrade Ubuntu to the next release. RESULT: - The user looses permissions for several basic actions in the system. ProblemType: Bug DistroRelease: Ubuntu 13.10 Package: policykit-desktop-privileges 0.16 ProcVersionSignature: Ubuntu 3.11.0-12.19-generic 3.11.3 Uname: Linux 3.11.0-12-generic x86_64 ApportVersion: 2.12.5-0ubuntu2 Architecture: amd64 Date: Tue Oct 15 20:20:55 2013 InstallationDate: Installed on 2013-10-09 (7 days ago) InstallationMedia: Ubuntu 13.10 "Saucy Salamander" - Beta amd64 (20131008) MarkForUpload: True PackageArchitecture: all ProcEnviron: LANGUAGE=en_US TERM=xterm PATH=(custom, no user) LANG=en_US.UTF-8 SHELL=/bin/bash SourcePackage: policykit-desktop-privileges UpgradeStatus: No upgrade log present (probably fresh install) To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/gdm/+bug/1240336/+subscriptions -- Mailing list: https://launchpad.net/~touch-packages Post to : touch-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~touch-packages More help : https://help.launchpad.net/ListHelp