Comment 12 for bug 951000

It seems that the issue is somehow related to the Apparmor profile, but unfortunately by disabling it and logging in as guest I've fixed it and now, even after I re-enable the profile lock is disabled [1]

I have no idea what the actual error was, although there are quite a few apparmor audit messages when the session is started:

[ 54.554230] type=1400 audit(1334831715.697:30): apparmor="DENIED" operation="open" parent=1 profile="/usr/lib/lightdm/lightdm/lightdm-guest-session-wrapper" name="/proc/2665/cmdline" pid=2660 comm="dbus-daemon" requested_mask="r" denied_mask="r" fsuid=132 ouid=0
[ 54.554593] type=1400 audit(1334831715.697:31): apparmor="DENIED" operation="open" parent=1 profile="/usr/lib/lightdm/lightdm/lightdm-guest-session-wrapper" name="/proc/2666/cmdline" pid=2660 comm="dbus-daemon" requested_mask="r" denied_mask="r" fsuid=132 ouid=0
[ 54.555207] type=1400 audit(1334831715.697:32): apparmor="DENIED" operation="open" parent=1 profile="/usr/lib/lightdm/lightdm/lightdm-guest-session-wrapper" name="/proc/2667/cmdline" pid=2660 comm="dbus-daemon" requested_mask="r" denied_mask="r" fsuid=132 ouid=0
[ 54.555823] type=1400 audit(1334831715.697:33): apparmor="DENIED" operation="open" parent=1 profile="/usr/lib/lightdm/lightdm/lightdm-guest-session-wrapper" name="/proc/2668/cmdline" pid=2660 comm="dbus-daemon" requested_mask="r" denied_mask="r" fsuid=132 ouid=0
[ 54.560074] type=1400 audit(1334831715.701:34): apparmor="DENIED" operation="open" parent=1 profile="/usr/lib/lightdm/lightdm/lightdm-guest-session-wrapper" name="/proc/2671/cmdline" pid=2660 comm="dbus-daemon" requested_mask="r" denied_mask="r" fsuid=132 ouid=0
[ 54.580359] type=1400 audit(1334831715.721:35): apparmor="DENIED" operation="mount" parent=1 profile="/usr/lib/lightdm/lightdm/lightdm-guest-session-wrapper" name="/tmp/guest-1MB45i/.gvfs/" pid=2684 comm="gvfs-fuse-daemo" fstype="fuse.gvfs-fuse-daemon" srcname="gvfs-fuse-daemon" flags="rw, nosuid, nodev"
[ 62.044159] type=1400 audit(1334831729.207:36): apparmor="DENIED" operation="open" parent=1 profile="/usr/lib/lightdm/lightdm/lightdm-guest-session-wrapper" name="/proc/2575/stat" pid=2819 comm="bamfdaemon" requested_mask="r" denied_mask="r" fsuid=132 ouid=0
[ 62.044181] type=1400 audit(1334831729.207:37): apparmor="DENIED" operation="open" parent=1 profile="/usr/lib/lightdm/lightdm/lightdm-guest-session-wrapper" name="/proc/1473/stat" pid=2819 comm="bamfdaemon" requested_mask="r" denied_mask="r" fsuid=132 ouid=0

but this could be red herring

I'm closing the bug for now, Seb has said that he'll try to reproduce it on the newly installed system from the daily CD, and if he can he'll reopen it. For now I don't see how we can even track it any further.

[1] gsettings get org.gnome.desktop.screensaver lock-enabled returns "true" but the "Lock Screen" menu entry is gone, ctrl+alt+L does nothing and lock related options in the "Lock & Brightness" settings panel are disabled.