Solution for changing Big Sur login wallpaper to custom.

There *is* a procedure in the discussion of this issue that modifies the start-up screen as well, see https://discussions.apple.com/thread/252056512?answerId=255286668022#255286668022, but you have to turn off SIP and SSV, and likely the changes void AppleCare.

That looks like it may well work, pauclaude.

The potentially tricky part is the way the boot disk, on Big Sur, is a disk image, and the way the Preboot system keeps a signature for that disk image.

So. It is possible that the procedure you have given may work.

However, it’s also quite possible (perhaps even likely) that the procedure will fail.

Please let us know how well (or poorly) it works!

Doesn't work. iMac Pro Big Sur 11.5.2 -- comes up with that absolutely ghastly coloured screen, go to sign in and picture I chose appears, then progresses to desktop picture I chose. But still seeing that awful log-in garish background someone dreamed up when drunk or high. Whatever made Apple think anyone wants to look at that! By the way the drunk screen is not in the pictures folder and no idea where they have put it. If we knew what it was called we could perhaps haul it to the trash.

I’m not applewarm, just thought I’d help out - you’re right, ganni0996. From my experience if you turn on FileVault again, the login pic will revert to the bright-colored background.

Basically, jamesfromsherman, you converted your system to a Single User System.

Then the Login Screen is skipped, for the Lock Screen of the single user.

Hi garywi,

Yes, you have to deactivate FileVault for this to work and also have a single user login.

LdyGatr,

See my post above. In OnyX go to Parameters > Login and assume you'll click Selectto change the background image.

Hope this helps.

applewarm wrote:

1. Just sharing a solution I've found on Stack Exchange. Credit to whoever discovered it.

System Preferences > Users & Groups.

2. Open lock to make changes.

3. Right click on user in left column > Advanced Options.

4. Copy UUID value.

5. Go to /Library/Caches/Desktop Pictures.

6. If it doesn't exist create Desktop Pictures folder.

7. Inside Desktop Pictures create folder with UUID value as name.

8. Right click on folder > Get Info.

9. Open lock to make changes.

10. Grant permission to Read & Write to user, admin, everyone.

11. Make sure FileVault and Guest user are deactivated.

12. Change desktop wallpaper.

13. Restart computer.

Big Sur will now always create a lockscreen.png file in the UUID folder matching the current wallpaper.

Tested on a 2018 MBP and works perfectly.

Enjoy!

Can we see a screen shot of your modified folder as you indicate:

 /Library/Caches/Desktop Pictures

Here is what I see by default:

for clarity are you saying create another sub folder with a tile of the UUID?

Do you place another picture in that folder, do you name with UUID number or do you name it "lock screen.png" ?

Do you delete the old "lock screen.png" ?

Right now that "lock screen.png" matches my login background, not the colorful Big Sur restart wall paper...?

This does not work for me. I found the folder already created and the lockscreen.png file exists. I opened the .png file and it is my current desktop picture. When I start my computer and I'm presented with the two users and guest I have the hideous background. Once I click a user to enter the password the background changes to that user.

The hideous background picture appears to be Big Sur Graphic Light in the desktop background options. I wonder if I find that file location and just rename it and substitute a background I like and name that in it's place. Then when it loads the picture it can load what I like?

I found the System/Library/Desktop Pictures folder and attempted to rename the Big Sur Graphic.heic file and replace it with a suitable replacement. Unfortunately even though I am an administrator I don't have permission to modify the file.

The other method did not work for me as I have multiple users and a Guest account.

Did you always have a true Single User setup, without even a Guest user, applewarm?

If so, then something appears to have interfered with the macOS being able to recognize your setup as being Single User.

Ever since Apple allowed for multi-user setups, Apple has tried to preserve the Single User behaviors, as much as they reasonably could.

Unfortunately, rather than using some explicit “Single User” setting, this behavior has relied upon the system being able to recognize a Single User setup. Therefore, the behavior can be subject to little things that can interfere in the recognition of Single User setups.

(An explicit “Single User” setting has its own issues, such as difficulty adapting to user changes.)

Hi Soren,

in reply to your question: I changed the desktop pictures of BOTH users on the MacBook using the recommended Apple procedure under Preferences..Desktop. After that change and reboot, the Desktop and individual user login screens changed to match the individual users selected picture.

What didn’t change was the “boot” screen where the MacBook starts after reboot that has the user selection. Still same old crazy. Once you click on an individual user from the ugly screen you go to the login screen with the nice new picture while you put in your password/fingerprint, then on to your matching desktop. That’s my best description.

I did not revert or change anything back before I followed the procedure trying to change the boot screen. During the procedure I found that the HD/library.... already had two UUID folders, one for each user containing the .png file. The png file was a different picture, the one selected for that user. Nothing to add or change ! At that point I added a third UIID folder using a UUID I found for the Default user and put a .png there. No help so I deleted it. At this point I can’t thing of anything else to do. I guess that Apple is right for SOME users for some undefined reason it can’t be changed or there’s a missing piece of information in the procedure that’s biting some users. Ouch ! :)