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I'm on trusty and I can't lock my computer by any means. When I press Super+L or use the Lock button in the panel, the behavior is the same: the screen turns black and if I move the mouse, my desktop pops up again, without ever locking.

I'm on Trusty x86 and I confirmed that if I create a new user account, I can lock the screen in that account. I checked the Lock settings in "Brightness & Lock" and everything is grayed out, as the following screen capture shows. How can I enable the usual system lock again?

enter image description here

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up vote 3 down vote accepted

Do you use Unity Tweak Tool? You might have this option enabled and not even know about it:

enter image description here

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You're right. How did this get enabled in the first place? I re-enabled locking in UTT and now Ubuntu is locking smoothly again. Thanks. – ecc Apr 18 '14 at 21:19
If you have a separate home partition it might be because of old settings from previous versions. I'm not really sure. – Canha Apr 18 '14 at 21:25
I had the same problem, and could only fix it by installing this tool. The tool could not have caused my issue, but it fixed it. – Jeff Mar 4 at 3:57

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