Mac OS X Lion: The Missing Manual

Changing Permissions

Permissions is a largely invisible, but hugely important, Mac OS X and Unix feature. The behind-the-scenes permissions setting for a file or folder determines whether or not you’re allowed to open it, change it, or delete it. Permissions are the cornerstone of several important Mac OS X features, including the separation of user accounts and the relative invulnerability of the operating system itself.

As you know from Chapter 12, you can get a good look at the permissions settings for any file, folder, or disk by highlighting it and choosing File→Get Info in the Finder. But even there, you’re not seeing all the permission settings Unix provides, and every now and then, you might want to. Suppose, for example, that you’re a teacher in charge of a computer lab containing 25 Macs. On each computer, you’ve created Standard accounts (see Chapter 12) for five students, for a total of 125 student accounts.

Soon after the students start using the lab, you notice a bit more giggling and frantic typing than you’d expect from students researching Depression-era economics. You nonchalantly stroll to the end of the room and do a quick about-face at one of the desks. Aha—iChat! Horribly depressed by the comments you read there regarding your fashion sense, you vow to keep students from using that application ever again.

You have several options:

• Delete iChat from the Applications folder. Unfortunately, the Computer Club meets in your classroom after school, and its members routinely ...