Unable to execute power management functions due to missing pam.d include

[Graeme Merrall]

I have a clean install of 14.04 server and install lxdm and lxde. I was unable to shutdown/reboot the machine due to an issue. Attempting to shutdown the machine generated an error "GDBus.error:org.freedesktop.DBus.Error.AccessDeined:operation not permitted"

To resolve this issue I had to manually add
session required pam.systemd.so" to /etc/pam.d/lxdm (this file is provided by lxdm)

To reproduce
1. Install a clean14.04 server and install lxdm and lxde
2. In the bottom right corner of the screen, click the little power icon and click shutdown

Observed: Error as described above

After editing /etc/pam.d/lxdm execute the above steps again and the machine will shutdown successfully.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: lxdm 0.4.1-0ubuntu6
ProcVersionSignature: Ubuntu 3.13.0-24.46-generic 3.13.9
Uname: Linux 3.13.0-24-generic x86_64
ApportVersion: 2.14.1-0ubuntu3
Architecture: amd64
CurrentDesktop: LXDE
Date: Sat Apr 19 12:17:55 2014
ExecutablePath: /opt/google/chrome/chrome
InstallationDate: Installed on 2014-04-19 (0 days ago)
InstallationMedia: Ubuntu-Server 14.04 LTS "Trusty Tahr" - Release amd64 (20140416.2)
SourcePackage: lxdm
UpgradeStatus: No upgrade log present (probably fresh install)
mtime.conffile..etc.pam.d.lxdm: 2014-04-19T11:52:28.769795