appletgnomesession
For some reason, sometimes when I log in the top panel applets appear garbled. For instance the session applet is missing its icon, and the current username is repeated twice. This doesn't happen very often, but when it does the session applet is not responsive so I can't get to the log out menu option.
Is there any other way to log off the current user other than using the (non working) session applet?
This apparently results from a 10.10 repository error where nvidia-current update was botched and as a work-around I installed driver from nvidia. This resulted in a botched 10.10>11.04, then a botched 11.04>11.10, then a botched 11.10>12.04 release upgrade. It kind of incredible that the resulting 12.04 would boot at all. Remarkably, the same thing on a 32bit system worked perfectly. The solution apparently will be to fix the 11.04 so the following upgrades will work, if that is possible. Fortunately I have backed up each step.
UPDATE:
Mismatch seen after upgrading without nvidia-propietary: 
UPDATE This now seems to be associated with 12.04's inability to support a second monitor (at least in amd64 with nvidia graphic adapters). These occur when adding/deleting 2nd monitor (screen1) using nvidia settings and logging on/off. Bug reports have been filed, Bug #1002641 and Bug #1001712 and possibily related to Bug #1002602 and Bug #729979
This also occurs with Unity.
UPDATE Bug #1002641 is getting a little attention but nobody is assigned to work on it. After today's update, I now have the Unity Dash Totem on my Gnome fallback/classic screen obscuring the Gnome top panel and pretty much making 12.04 useless. Thank goodness I have a working 10.04 also running so I can get some work done.
if so, how do i disable it?
You don't want to disable the Magic SysRq!
The key combination AltSysRq triggers the Magic SystemRequest and allows to enter combinations of single keys to shut down your system in a controlled way, even when everything else has become completely unresponsive.
This is your life-saver. Don't throw it over board ;)
/proc/sys/kernel/sysrq. A value of 0 disables everything, so
echo 0 > /proc/sys/kernel/sysrq
will do the job. But you have been warned ;)
kernel.sysrq = 0
to /etc/sysctl.conf. either that or create a file in /etc/sysctl.d/* with the mentioned line.
Best Answer
Press Alt+F2, type
gnome-session-save --logout, then hit enter. If an application is blocking logout, trygnome-session-save --force-logout