Another look at login window backgrounds

One of the things many OS X users like to do is replace the login window background—the image you see behind the login screen. In OS X 10.4 and earlier, the process was simple: just replace the file named Aqua Blue.jpg in /Library/Desktop Pictures with one of your own design. In OS X 10.5, though, that simple solution is gone.

As mentioned in Dan Frakes’ excellent Leopard’s first tweaks article, there are a couple of ways to modify your Leopard login window background: you can muck about with a system-level file (not necessarily a good thing to do), or you can use the $5 Visage Login to do that, and much more (though it also modifies system files, but it’s safer than doing so yourself).

I’ll show you a third way to change your login window background—one that works in OS X 10.4 and 10.5, and doesn’t require replacing a system file on either system. This is the preferred way to change the image, even though it’s more technical than the other solutions. By not modifying a system-level file, you’ll never lose your login window background to a system update, for instance. There’s even evidence that this change will survive a major upgrade, as a reader has told me that the custom background was intact after upgrading to Leopard from Tiger.

To get ready for this change, you need two things: an image you’d like to use, sized to your default screen resolution, and an open Terminal window. Once you have the picture you’d like to use, there’s a secret as to where to store the image: save it in your user’s Public folder, at the top level. The other alternative is to put it in the top-level Library -> Desktop Pictures folder, but that sort of defeats the purpose of not modifying the system-owned folders, doesn’t it? The reason your picture needs to go in your Public folder is that it needs to be available to all users. (There are workarounds, but they require mucking about with permissions. And why bother if there’s no need?)

Once the image is ready and saved in the right spot, switch to the Terminal window, and enter this command:

sudo defaults write /Library/Preferences/com.apple.loginwindow DesktopPicture "/Users/your_user/Public/myloginwindow.jpg"

You can copy the above (triple-click it, then press Command-C), and then paste it into the open Terminal window. However, before you press Return, you’ll need to edit it a bit for your particular setup. Move back with the Left Arrow key until you’re at the / after your_user.

Now press Delete to erase that bit, and enter your short username instead. Using the Right Arrow, move to the end of the filename, and replace it with the name of your file—make sure you leave the last quotation mark in place. For instance, here’s what that portion of the command looks like on my system:

"/Users/robg/Public/LeopardX.jpg"

Once you’re sure everything looks right, press Return and provide your admin password when asked. If you typed everything right, Terminal won’t echo anything back after you enter your password—you’ll just get the command prompt back.

To test your new background, the easiest thing to do is enable Fast User Switching (in System Preferences -> Accounts, then click the Login Options item below the account list). In the menu bar, click the Fast User Switching entry and select Login Window. If the command worked, you’ll see your new login screen. If it didn’t, you’ll probably see a solid blue background instead.

If it didn’t work, try it again and make sure you have the command correct, with the proper filename (and filenames in Terminal are case sensitive).

If you ever tire of your custom screen, you can restore the default version by deleting the entry you created in the preferences file:

sudo defaults delete /Library/Preferences/com.apple.loginwindow DesktopPicture

The next time you see the login screen, it should be the familiar Aqua Blue (10.4) or deep space picture (10.5). Although this method is perhaps a bit more complicated than others, it’s a very safe way to replace the login window image without fear of damaging your system.

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