Wallpaper does not cover all screen on Mac mini 2018 and 5k screen

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Wallpaper does not cover all screen on Mac mini 2018 and 5k screen

I have the LG 5k screen connected to a Mac mini, and every couple of days the wallpaper does not cover the whole screen. The only way I can make it full screen again is to logout and log back in.

I've tried many things:

changing the wallpaper but it is not saved when I log back in
trying to put a colour instead of picture, but it is reverted back on each login as well.

Is there a way to force a full screen wallpaper, or to force keeping my settings? (like no wallpaper but a background colour)

Mac mini 2018 or later

Posted on Jan 26, 2020 5:03 AM

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Answer 1

Old Toad

Level 10

207,463 points

Jan 28, 2020 11:05 AM in response to Gouarf

Boot into Safe Mode (Use Safe Mode to isoloate issues with your Mac) and set the wallpaper there. Reboot normally and check to see if the problem persists.

NOTE: Safe Mode boot can take up to 10 minutes as it's doing some system cache cleaning, volume verifying and directory repairing.

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Answer 2

Jan 27, 2020 10:17 AM in response to Gouarf

Gouarf wrote:

So I tried that yesterday, and it worked on the first boot.

Then today I start the Mac, and bingo I have a thumbnail of a wallpaper.

Get help with video issues on external displays connected to your Mac - Apple Support  https://support.apple.com/en-us/HT201177

Using 4K displays, 5K displays, and Ultra HD TVs with your Mac - Apple Support  https://support.apple.com/en-us/HT206587

Use the LG UltraFine 5K Display with your Mac https://support.apple.com/en-us/HT207448

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Answer 3

Jan 28, 2020 11:04 AM in response to Gouarf

Gouarf wrote:

I have to log out and log back in again.

But this time, instead of displaying the image full screen like it normally does, it actually decided to read my preferences and displayed the solid colour in place. On both desktops.

Of course we care Gouarf, it is an unusual situation .

If the issue returns try a safe boot to clear system cache—

Try a SafeBoot https://support.apple.com/en-us/HT201262

Takes noticeable longer to get to the login screen, does a 5-15 minute disk repair before it fully boots up, and certain system caches get cleared and rebuilt, including dynamic loader cache, etc. Login and test. Reboot and test will take a little longer as caches get rebuilt.

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Answer 4

Jan 29, 2020 1:15 PM in response to Gouarf

The first thing to do is to go to Desktop & Screen Saver in System Preferences. Then go to the Desktop screen and look at the drop-down menu. Mine currently says "Fill Screen" (Apparently this means the system gets to choose.) but you might want "Stretch to Fill Screen" or "Fit to Screen". See https://support.apple.com/guide/mac-help/change-desktop-preferences-mchlp1103/mac If this isn't helpful, you might want to send a screen capture of the Desktop tab.

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Answer 5

Jan 26, 2020 7:22 AM in response to Gouarf

Try resetting NVRAM/PRAM http://support.apple.com/kb/ht1379

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Answer 6

Gouarf Author

Level 1

9 points

Jan 28, 2020 1:25 PM in response to Old Toad

Thank you for your help guys, much appreciated :)

So, we're onto something there. I started in safe mode and the wallpaper was there... full screen.

And now the issue is the other way around: the screen was limited to the size of the wallpaper!

or is there a 4k limit in safe mode?

While in safe mode:

At that point, I changed the wallpaper to a solid colour, since it looks like that could be a temporary resolution I get when I start the Mac. I always thought it was funny how the startup was not sleek like it is on my previous Macs. The screen is flickering like 4 or 5 times when I log in.

Anyway, I rebooted and after the flicker and what looks like a few resolution change, I finally get the black wallpaper I asked for.

And the resolution is right:

Seriously I'm getting so many weird things with this mac mini, I really wish I bought another iMac instead

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Answer 7

Gouarf Author

Level 1

9 points

Jan 27, 2020 10:07 AM in response to leroydouglas

Thank you for your reply

So I tried that yesterday, and it worked on the first boot.

Then today I start the Mac, and bingo I have a thumbnail of a wallpaper.

... and I used to praise Apple to my friends...

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Answer 8

Gouarf Author

Level 1

9 points

Jan 27, 2020 10:24 AM in response to leroydouglas

Thank you for your reply, but I cannot find anything related to my issue in these documents.

Also I can't seem to find why it cannot keep a colour as a background: on every restart it insists on changing my preference and displaying the default picture again.

Apart from that the screen works perfectly fine at 5k. Well the screen itself is fine; the graphics card is dead slow at this resolution though.

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Answer 9

Gouarf Author

Level 1

9 points

Jan 28, 2020 10:52 AM in response to Gouarf

Probably nobody cares but here's an interesting development:

I've changed the background to a solid colour (reminds me of Windows XP somehow) and I've done it on the two desktops I have defined (just in case). Log out, and back in, all fine.

Today I boot up the Mac:

As usual the stupid picture is covering half the screen and I have to log out and log back in again.

But this time, instead of displaying the image full screen like it normally does, it actually decided to read my preferences and displayed the solid colour in place. On both desktops. How nice

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Answer 10

Gouarf Author

Level 1

9 points

Jan 30, 2020 12:56 PM in response to Gouarf

I had an idea while reading articles about other people having weird issues right after logging in, and I tried to disable FileVault.

The Mac is a desktop machine, so I'm not going to forget it in a cafe...

Anyway, I did and rebooted a few times, and I can confirm the flickering right after logging in is gone, meaning that the resolution is not changing many times like before.

Let's see if that fixes it...

Also all the technical documentation I've read about the cheap-*** graphics card included in the Intel CPU is that the maximum resolution is actually 4k. Meaning Apple had to develop some kind of software hack to get 5k out of it.

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Wallpaper does not cover all screen on Mac mini 2018 and 5k screen

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