Ever noticed the Library folder inside your Home folder and wonder what it was all about? Time and again, for certain tricks you have to go to specific locations in the library, and you do so without understanding the why and how of it. No not you. I know you are experienced enough to understand what the library folder, which is why I’d suggest you pass up this guide to your newbie Mac friends.
Back to the Library folder, there’s in fact three of them. There’s two systemwide Library folders, one placed inside the Mac HD, and the second one is in the Mac HD » System folder. The third one’s for each user account on the system placed inside the Home folder. I’m going to focus more on the one in the user home folder, as tampering with the one at System level might create havoc in your system.
While Mac applications are single units of functionality, when you first launch an app it creates certain files across your system. The two main places where you will find these files are:
Almost every application you launch will create a preference ‘.plist’ file in the Preferences folder, sometimes more than one. This is an XML file which stores your preferences you’ve changed in each application. If for instance you want to make an application behave like it was just launched on your Mac, just delete the respective .plist file and it’ll all go back to square one.
If an application needs to store data, not the kind you can carry around, it will create a folder in the Application Support folder. For instance, Things will store its database here, Clipboard managers will store past clips, and FTP clients will store favourites and bookmarks. If you ever need to transfer an application to another Mac and move all that data, these are the folders you need to copy. This folder is also important for troubleshooting apps. For instance, Google Reader in my Eventbox app wasn’t updating. So I just deleted the Google Reader folder from the App Support » Eventbox folder, and everything refreshed just fine.
Preference panes are installed on a per user basis, or systemwide. While you can uninstall Preference panes just by right-clicking them in System Preferences and selecting delete, if you want to move them to another system, this is the folder they’re placed in.
Similar to Preference Panes, you can also access the widgets that are installed in your system. You can move them from the Home folder to the systemwide preferences to make widgets accessible to every user in the system. You can even use them to backup or share a widget collection, as sometimes the developers stop serving an old widget.
Whenever you right click on an image in Safari and set it as a desktop background, the original is immediately saved in the Safari folder inside your Library. Sure you can grab it as a screenshot: Cmd+Shift+4 » Spacebar and clicking on the desktop. But this is not the full resolution file that you downloaded as it only grabs till the dimensions of your screen. There’s more goodies in this folder including Bookmarks and History plist files which you otherwise cannot export with Safari’s default feature set.
Come Snow Leopard, Mail is said to be much improved. I don’t know how much of that is true, so I’ll mention this anyway. Mail app stores its data inside the Mail folder in your library. If it crashes and refuses to start up again, you can just delete this folder. You can even drill down into a specific account and delete only the Inbox folder. It will then retrieve all your Mail again from the server. If you have a Time Machine backup, all you need to do is replace this Mail folder with the one from few days ago and Mail will catch up. Saved me a bunch of times.
There’s of course a whole lot of junk in there you don’t want to know about. Hopefully this little guide will better help you understand how exactly each of these folders affects your Mac. If you have any other tips or suggestions with regard to them folders, do share.