Grant read/write permissions to 'system'

I am on Mountain Lion and was annoyed at how when I close my computer lid while on a full screen app and then wake the computer, the background for the password prompt is not my own choice of background but the default galaxy one.

To fix this, I modified the alias 'DefaultDesktop.jpg' in the CoreServices folder so that it referred to another image file in the same Desktop Pictures folder. To my dismay, when I tested the password prompt, I was greeted with a blank background.

I figured that the reason this is happening is because the DefaultDesktop.jpg alias does not have 'system' read/write permission, instead it has my own account read/write permission because I modified it, and 'system' is not included in the list of users so I can't edit the permissions and I can't add 'system' to the list of users either.

One way that I know will work is to go into the file permissions for the CoreServices folder, which already has system read/write permission and then use 'Apply to enclosed items' - but that will apply those permissions to every single file in the folder so I'm worried that this will mess up some other file. Is this a good idea or is there some other way that will change the permissions of that file only (I'm assuming it involves using the terminal)?

Thank you and please do not reply by saying 'you shouldn't mess around with system permissions, you will wreck your computer'. I know what I want to do and I'll be left with a blank password prompt background forever if I don't fix this.

Check out this Apple KB article: "How to enable Root user" LINK

Log on as Root and change the file permissions for that single file. Should work without messing anything else up. You can also do it with the terminal but it's best to do it while in the GUI where there is less chance of making a mistake.

Also, I believe there's a free utility floating around that can change the background for you. Mountain Lion Tweaks?

chscag said:

Check out this Apple KB article: "How to enable Root user" LINK

Log on as Root and change the file permissions for that single file. Should work without messing anything else up. You can also do it with the terminal but it's best to do it while in the GUI where there is less chance of making a mistake.

Also, I believe there's a free utility floating around that can change the background for you. Mountain Lion Tweaks?

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I did all of that and it worked perfectly, the file permissions are as they should be now, but I'm still getting a blank lock screen. I even changed the alias back to refer to the default Galaxy.jpg (still as root) and it's still blank. Restarting doesn't help either and that free utility appears to be for changing the login screen, not the lock screen.

It's not that I have anything against the aesthetics of a plain black lock screen, it's just that every time I unlock the computer I'll be reminded of this failed experiment...

Any other solutions, even if it's just for reverting back to how it was before?

use Onyx to set your favourite login background

beakerbeetle said:

use Onyx to set your favourite login background

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I specifically said I am not looking for a tool to change the login background, it's the lock background I'm talking about. Please read my question properly before attempting to answer. You're just wasting your own time.

I don't care anymore if there's no way to change the lock background, is there any way to revert it back to how it was (other than reinstalling the OS). Please help someone...

simplyfoods said:

I specifically said I am not looking for a tool to change the login background, it's the lock background I'm talking about. Please read my question properly before attempting to answer. You're just wasting your own time.

I don't care anymore if there's no way to change the lock background, is there any way to revert it back to how it was (other than reinstalling the OS). Please help someone...

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I'd help, but I'm afraid I may give the wrong answer and get reamed out for trying. Good luck with that.

lifeisabeach said:

I'd help, but I'm afraid I may give the wrong answer and get reamed out for trying. Good luck with that.

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OK that's just uncalled for. There's a difference between trying to help and the solution not working, and answering a whole different question to the one I asked, especially when I have thoughtfully warned about it beforehand to avoid people misinterpreting it that way.

But I'm not here to argue about this, if you are able to help then please do, just make sure you understand what I'm asking.

simplyfoods said:

OK that's just uncalled for. There's a difference between trying to help and the solution not working, and answering a whole different question to the one I asked, especially when I have thoughtfully warned about it beforehand to avoid people misinterpreting it that way.

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Actually it was called for. I don't doubt he was trying to help, and reaming him out for misunderstanding the problem is very undignified. The people who help here are unpaid volunteers and enthusiasts with widely varying degrees of technical know-how and even reading literacy. You are getting far more than you paid for here, so take the good advice, ignore the bad, and be gracious someone is trying.

I've been thinking about this problem some more and finally had time to sit down and experiment with it a bit. A permissions issue didn't make much sense to me. System, as far as I know, doesn't need permission to access anything. It may not be the explicit owner for a file, but ultimately it cannot be denied access.

The problem is the alias you made. It's not supposed to be an alias. It's supposed to be a symbolic link (symlink). These look the same in Finder, and Finder thinks they are the same thing, but the BSD subsystem doesn't know how to use an alias. Like I said, it's not easy to tell, but I made an alias and a symlink of Galaxy.jpg and compared the file sizes to the original I have in CoreServices. The size difference between the alias (at 176 KB) and the symlink (at 4 KB) is considerable. The original "alias" in CoreServices is 4 KB. That actually is a symlink.

So... how to make the symlink? There a freebie you can download named SymbolicLinker that can do the job. I have a tutorial somewhere here in the forums on how to use it. You can also do a web search to find the software. It comes with instructions.