Take Control of Permissions in OS X

As you see, there are nine basic permission settings, each of which can be turned on or off. That’s a total of 512 possible combinations!

Because the same combinations are used over and over, Apple wisely provides an extremely easy way of using the most common combinations. The convenient combinations provided by Apple are:

  • Read & Write: A user can see the contents of an item, and change it.
  • Read Only: A user can see the contents of an item, but cannot change it.
  • Write Only: A user can write to an item but can’t see its contents. This setting exists so that a folder can be turned into a Drop Box . A Drop Box is a folder other users can put items into, but only the user owner can open to take items out.
  • No Access: A user is denied all access to the item.
  • Any one of these four pre-defined settings can be applied to each of the three owner types via the Info window of the Finder.

    Choose a method of setting permissions

    You can set permissions in Mac OS X in more than one way. Namely, you can use:

  • The Info window in the Mac OS X Finder
  • Third-party tools
  • Unix commands
  • Each method has relative advantages and disadvantages, outlined below.

    Methods of Setting Permissions

    Method Advantages Disadvantages
    Info window Easier and more intuitive than Unix commands. Limited capabilities. Not as powerful or flexible as Unix commands.
    Third-party tools More features than the Info window. Not present by default. May require additional expense.
    Unix commands More powerful and flexible than the Info window. May be faster if you are familiar with Unix. Less intuitive than the Info window.

    Because the vast majority of users will get by just fine with the easier graphically based methods, I cover the Info window and third-party tools next; advanced Unix commands appear elsewhere in this ebook.

    Figure 1: Ownership and permissions for a typical file as viewed in the Info window.

    permissions in the Info window

    Set permissions using the Info window

    For simple tasks, set permissions using the Finder’s Info window. The Info window does not provide the degree of control that Unix commands do. You cannot, for instance, manipulate individual Unix permissions. However, setting permissions via the Info window is quite easy, and is perfectly adequate for most day-to-day situations.

    Set permissions with the Info window by following these steps:

  • Working in the Finder, select an item.
  • Choose File --> Get Info (Command-I). You may need to click the Ownership & Permissions triangle to reveal more detail, as shown in Figure 1 on the right.
  • Now, do one or more of the following:
    • Set access permissions: Choose your access permissions from the You Can pop-up menu. The menu item will be dimmed if you lack sufficient permissions to change the item.
    • Set owner permissions: Click the Details triangle to change permissions for owner, group, and others ( as shown in Figure 2 below).
  • A lock icon beside an item indicates that such a change requires administrator level privilege. Click the lock icon and provide the user name and password of an administrator account when prompted.

  • If the item you selected in Step 1 was a folder, and you wish to apply your changes to everything inside of it, click the Apply to Enclosed Items button at the bottom of the Details section.
  • Close the Info window.
  • Unix Equivalents of Info Window Access Settings

    Setting Effect on Files Effect on Folders
    Read & Write rw- rwx
    Read Only r-- r-x
    Write Only (Drop Box) Not applicable -wx
    No Access --- ---

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