Detected display settings are incorrect after hot-swapping monitors

OS X generally does a good job of detecting monitors and providing available screen resolutions, color depths, and other settings that are available for a certain make and model. In some instances, however, specific setups may prevent monitors from being

OS X generally does a good job of detecting monitors and providing available screen resolutions, color depths, and other settings that are available for a certain make and model. In some instances, however, specific setups may prevent monitors from being detected properly, which can result in the computer displaying either generic settings or a subset of the available settings for a monitor.

Apple Discussion Board member Quix77 writes:
"I've got a Mini running 10.5.6 with a 22-inch LCD that runs at 1,680x1,050 natively. I recently disconnected the Mac and plugged it to my standard definition TV for some old-school Nintendo gaming at 640x480 and it worked beautifully. Now, when I reconnect the Mac to my 22-inch LCD, the native resolution is no longer available. The best I can get is 1,600x1,200, which is not the native wide-screen resolution."

When you connect your computer to different displays, the windowserver process updates its settings to accommodate the new display for the specific make and model that is detected.

Sometimes hot-swapping displays can confuse the window server and cause the computer to show limited or improper settings for a display device, especially if a monitor of a different aspect ratio and screen resolution is used. These settings will be stored in the windowserver preference files and may be used each time the monitor is detected, which can result in the available monitor resolutions being incorrect even after restarting the system.

Though resolution problems call for PRAM reset attempts, this problem can persist even after the PRAM and other hardware settings have been reset, since it has to do with accessing stored settings that were previously detected for the monitor.

There are a couple of approaches to fixing this problem.

Fixes:

1. Shut down properly before swapping monitors.

If you are having problems with settings on one monitor after hot-swapping with another one, try connecting the second monitor and then shutting down before switching back to the one that has resolution problems. This should make the window server refresh the settings files, ensuring the monitor settings are "released" so subsequent monitors can be attached and detected.

2. Remove the windowserver plist files.

Removing the windowserver preference files and restarting the system should refresh the previously stored monitor settings with newly detected ones. Keep in mind that when doing this, specifics such as multiscreen arrangement will be reset; however, those can easily be set back up in the Displays system preferences. The windowserver preferences are the following files:

/Macintosh HD/Library/Preferences/com.apple.windowserver.plist
/username/Library/Preferences/ByHost/com.apple.windowserver.MACADDRESS.plist

NOTE: In the second file, "MACADDRESS" is the computer's Media Access Control Address or "Ethernet" address, which is a unique string of numbers that identifies your computer. In most cases this number should be the same for all files in the "ByHost" directory.

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