Permission and Sharing Do’s and Don’ts on Your MacBook
First, get the basics of sharing files and assigning permissions on your MacBook under your belt. Next, you need to master when to change permissions and why you should (and shouldn’t) modify them. Follow these common-sense guidelines when saving documents, assigning permissions, and choosing access levels:
Do use your Shared folder. The Shared folder is the center of proper document sharing. There’s a strong urge to create a new document in your Home folder, but you’re just making more work for yourself because you’ll end up copying that document from your Home folder to the Shared folder.
Instead of an extra step, store a document that’s intended to be shared in the Shared folder — where it belongs in the first place.
Don’t assign permissions just to protect a file from deletion. Remember, if all you need to do is prevent anyone (including yourself) from deleting an item, you don’t need to go to all the trouble of changing permissions.
Instead, just display the Info dialog for the item and select the Locked check box to enable it, which prevents the item from being deleted from the Trash until the Lock status is disabled (or you specifically click Remove All Items when emptying the Trash).
Do review the contents of a folder before changing permissions for enclosed items. That confirmation dialog doesn’t appear just for kicks. For example, if you set a highly sensitive, private document with permissions of No Access for everyone but yourself and then you apply less-restrictive permissions globally to the folder that contains the document, you’ve just removed the No Access permissions, and anyone can open your dirty laundry. (Ouch.)
Therefore, make sure that you open the folder and double-check its contents first before applying global permissions to the items it contains.
Don’t change permissions in the Applications or Utilities folders. If you have Administrator-level access, you can actually change the permissions for important applications such as Mail, Address Book, iTunes, and Safari, as well as their support files. This spells havoc for all users assigned to the standard-access level. Be polite and leave the permissions for these files alone.
Definitely don’t change System ownership. Mac OS X is stable and reliable. Part of that stability comes from the protected state of the System folder, as well as a number of other folders on your hard drive.
If you displayed the Info dialog for the System folder, you’ll see that the Owner is set to system, and the Group is set to wheel (a term from the UNIX world that encompasses all administrator accounts). Now, promptly close that Info dialog, without making any changes!
Never, never, NEVER change any permissions for any files owned by the System unless specifically told to do so by an Apple support technician. Do NOT monkey with System-owned items.
This last one is quite striking for a reason, so please heed the warning.