Hot Corners for Mission Control stop working

I set the upper right corner of the screen as a Hot Corner to activate Mission Control. However, some time after setting it, the Hot Corner stops working. Keyboard shortcuts still work.

Going back into System Preferences, changing the Hot Corner to some other action and then back to Mission Control resolves the problem temporarily. But eventually it fails again.

This wasn't always a problem with Lion. Mission Control Hot Corners used to work fine. I'm not certain, but I think the problem started with the 10.7.2 update. Either that, or some other software recently installed on my Mac is causing a conflict.

Any idea on how to resolve the unreliable Hot Corners?

27" iMac Core i3, OS X 10.7.2

Solution 1:

Had this issue November 2016 running OS 10.12.1 "Sierra" an additional symptom is that Mission Control was not launching. I fixed it by opening Activity Monitor, Quit the dock (force quit was not necessary). Went back to normal

Solution 2:

Just found the easiest solution! (for me at least)

I'm running on a MacBook Pro 13" together with a second screen and my hot corners would randomly stop working. But when I simply close the lid of the laptop, wait for a sec and then open it back up everything works again.

Hope that works for you!

Solution 3:

The problem could be related to a corrupted Dock Preferences file (Hot Corner settings are stored with the Dock preferences). If this is the solution, as a part of it, you will end up having to reset most if not all Dock related settings (scroll bar visibility, scroll bar behavior, auto hide, Dock screen position, icons in the dock, etc.).

Try this:

Open Terminal (Terminal can be found the Utilities folder. To locate the Utilities folder, in Finder, click Go -> Utilities) Type in the following commands:

mv ~/Library/Preferences/com.apple.dock.plist ~/Desktop/
killall "Dock"

At this point, open System Preferences and reset your Dock preferences and set the hot corners. Hopefully this will work for you.

Command Explanation: The first command moves the existing Dock preferences file to the Desktop to serve as an improptu backup. The second command quits the Dock. Mac OS will instantly reopen the Dock with a fresh preferences file.

If this did not work, you can optionally restore your old preferences file with the following commands:

In Terminal:

rm ~/Library/Preferences/com.apple.dock.plist
mv ~/Desktop/com.apple.dock.plist ~/Library/Preferences/
killall "Dock"

Solution 4:

I had the same problem where the hot corners worked for everything but the screensaver, and this appeared after I was forced to reboot when the MacBook Pro locked up.

I tried the "delete the .plist" file solution, even though I'd lose all of my Dock settings, but it didn't fix it.

I used the Disk Utility to repair the permissions on the hard drive (select the disk on the left pane, and click the "Repair permissions" button at the bottom of the right pane), and then rebooted again.

This got my screensaver working again...and I didn't have to sacrifice all of my Dock settings.

Solution 5:

Broke for me in 10.14, and just killing the dock wasn't enough. In Terminal:

defaults write com.apple.dock mcx-expose-disabled -bool FALSE

killall Dock