Solution for changing Big Sur login wallpaper to custom.

Hi! This is what I exactly did :)

1 System Preferences > Users & Groups > Click the lock to make changes > On the left box thingy, right click on your photo > Advanced Options... > Copy your UUID

+ Now, before you leave Users & Groups, make sure your Guest account is off

2 Go to Security & Privacy > Turn off File Vault

+ Note: Never turn this on again, it'll revert to Big Sur's default login screen background

3 Go to Finder > Find "Go" on your menu bar > Choose "Go to the folder"

4 Type "/library/caches" then click "Go"

5 Click on Desktop Pictures > check if there is a folder inside named after your UUID > click on the folder with your UUID and check if there's a photo named "lockscreen.png" inside

+NOTE:

If there is a desktop pictures folder and a uuid folder in it and a lockscreen.png in the uuid folder, ignore then proceed to the next step

If there is no Desktop Pictures folder, make one and create a folder in it with your UUID as the folder name

6 Go back to Caches (to where the Desktop Pictures folder is) > right click on Desktop Pictures folder > Get Info > Click the arrow on Sharing & Permissions > Set the system, admin and everyone to read and write

7 Close the **** thing

8 Choose the desktop picture you're after

9 Restart your mac

Hope this helps!

Tried everything everybody here has tried; no joy. Using a late 2014 Mac Mini, and while Big Sur has made some very noticeable improvements, this login screen is just horrifying. Not only does it sear the eyeballs first thing in the morning, it's something that looks like it belongs on a five-year-old's school computer. Very unprofessional.

It would be tolerable if we could at least change it as we can desktop backgrounds and screen savers, but apparently we can't be trusted to change our own login background as well.

Apple... time to fix it. I'm surprised no one pitched a fit during the Beta and Gold Master processes.

i'm on big sur. my login screen matches the desktop pic. i didn't change any settings or modify any folders. it's been that way since the second 10.15.7 update. in a different thread i was explained that my mac was doing this because i use only my admin account and guest users are turned off.

Medic7235 and @All:

I was doing some “poking around” on my Big Sur system, and, I believe, I have found the relevant images: they are within /System/Library/Desktop Pictures.

Most of the images are .heic (HEIF Image) files, or Aliases to such. (The Aliases access individual images from within the main HEIF Images.)

The brightly colored image is Big Sur Graphic.heic.

Well, Medic7235, even as a system Administrator, you cannot go around changing files, “willy-nilly”.

The macOS requires a few more steps for making such changes.

Since the System is on a Read-Only Volume, I wouldn’t be surprised if modification is precluded without extraordinary procedures. (In fact, for Big Sur, not only is the Volume Read-Only, but it contains a disk-image file, rather than the filesystem itself. Extra measures against modification, it would seem. Or, it may actually help facilitate mapping to memory. Or both.)

Note: I haven’t attempted such a change, myself.

weird thing is that I had activated the root user and tried it with root rights and even that did not work. I could not even chmod, although root is supposed to be owner.

Any idea how to replace that file by something more appealing?

juergenl wrote:

weird thing is that I had activated the root user and tried it with root rights and even that did not work. I could not even chmod, although root is supposed to be owner.

Any idea how to replace that file by something more appealing?

Earlier in this thread it was mentioned that the System files are read only and also as mounted image to prevent them from being modified. This seems to be preventing our image file swap approach.

Thanks for the fix! it works!

> Make sure FileVault is off.

> Make Sure Desktop Pictures folder have Read and Write access like the UUID folder

Restart then put the FileVault on again!

No more annoying wallpaper like we are living on Windows 95 era! :)