Why might you want to do this, you ask? The most common scenario is that something’s gone wonky with files or folders in your Home folder; you try to save something to your Desktop, say, and your Mac tells you that you don’t have permission to do so.
Yuck!
So after the wailing and gnashing of teeth, what comes next? Well, you could invoke the Get Info window (which I’ve written about in the past) to change the permissions for that individual item, but I think it’s easier to just use the built-in repair tool in case other things have gone wrong as well. So to access that tool, restart your machine. When the screen turns black, hold down the keyboard shortcut Command-R. That’ll take you into what Apple calls OS X Recovery, where you can perform all sorts of useful tasks, like reinstalling the operating system, restoring from Time Machine, and so on. To repair your Home folder permissions, start by clicking on the “Utilities” menu at the top of the screen and choosing “Terminal.”
Yes, yes, I had to take a picture of my screen. So sue me.
When the Terminal window appears, type in “resetpassword” (with no quotes and no space), and press Return.
On the next window, click on the name of your volume (usually “Macintosh HD”), then select your user account name from the drop-down, as below. Finally, click the button on the bottom section labeled “Reset Home Folder Permissions and ACLs.”
Wait until the process finishes, and you’re good to go. Afterward, you’ll want to click on the Apple Menu at the upper-left corner to restart your machine, and you can check to be sure that all is well with your formerly misbehaving permissions!