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Repairing Permissions?

W

Wilson

macrumors regular
Original poster
I have a newbie question.

What are permissions and why is it good to repair it after a update to the OS?
I have no idea what permissions are 😕

Thanks.
 
Wilson said:
I have a newbie question.

What are permissions and why is it good to repair it after a update to the OS?
I have no idea what permissions are 😕

Thanks.
Click to expand...

Some people exaggerate the importance of repairing permissions, but doing it once in a while is a good idea. Before and after every update is definitely more than is necessary. First let me give you an explanation (don't worry, I didn't know what they were at first either):

Unix (the core of OS X) uses a complex set of "permissions" for every file which basically specify what users have what privileges for this file. For example, the administrator might have read, write, and execute privileges; anyone else, however, might only be allowed to execute.

It sounds odd that these could cause problems, but the system is so complex and there are so many different files that sometimes incorrect permissions can cause serious glitches.

I recommend repairing permissions about once a month. To do this, go to /Applications/Utilites. In your Utilities folder, find the program "Disk Utility." Launch it and select your hard drive on the left. Then click "Repair Disk Permissions." Let this run, and you're done! It's that easy.
 
Note also that forced restarts, power failures, etc. can muck with your files, and Repair Permissions can help here as well.
 
titaniumducky said:
In your Utilities folder, find the program "Disk Utility." Launch it and select your hard drive on the left. Then click "Repair Disk Permissions." Let this run, and you're done! It's that easy.
Click to expand...
That's the avg. quick and easy way to repair permissions. The problem with using that method is: As you repair permissions for your system, that same system is also running. So while you are running permission repairs, they still could be changing. That's why I only repair permissions from the OS X CD (or from one system to another), but not from system to self. To do it that way: Boot from the CD, go to Installer > Disk Utility, and continue using the quoted procedure.
 
Every file on your hard drive has permissions to say which programs are allowed to access it and which aren't. Repair permissions justs scans the HD and makes sure each prog has access to the files it needs.
 
King Cobra said:
That's the avg. quick and easy way to repair permissions. The problem with using that method is: As you repair permissions for your system, that same system is also running. So while you are running permission repairs, they still could be changing. That's why I only repair permissions from the OS X CD (or from one system to another), but not from system to self. To do it that way: Boot from the CD, go to Installer > Disk Utility, and continue using the quoted procedure.
Click to expand...

Actually, Apple recommends against doing that. If you boot from the cd and do a repair of permissions, it can mess things up if you're using a newer version of the os (ie. booting with 10.3 and repairing a drive thats running 10.3.5). The permissions can be changed by updates to the os.
 
Upon reading that, I decided to review Apple's kbase as to which type of repairing permissions to do (to confirm that one method is better than the other). Nothing relevant. Then I went to Apple's discussion forums. Again, nothing relevant. I did find a variety of help topics/FAQs that said to repair permissions from OS X, and a few others saying to do it from the CD, but I didn't see any explicit views/facts favoring one method over the other. So how do you know Apple recommends one over the other? Or, more importantly, how does Apple conclude that one method is better than the other...if no such relevant information is available on Apple's site?
 
*Repair Permissions*

As jsw noted above, force reboots can cause permissions to sometimes be wrong. The only real time that you need to repair permissions otherwise is after installing something that requires your admin password. Repairing permissions does NOT (I repeat NOT) descend into your /Users hierarchy. So if you are having troubles with permissions in your home directory, acquaint yourself with "chown" and "chmod". Repair permissions isn't going to help you with that.

"Repair Permissions" simply reads the BOM (Bill of Materials) of each entry in /Library/Receipts. The BOM contains (amongst other things) the originally intended permissions for the package. It compares these to the current permissions and "repairs" the current permissions if they differ from the BOM. Also as noted, this becomes quite the red herring for some people as a 'maintenance step'. This is not necessary unless you can't remember to run a repair permissions when it's needed. And finally, my choice of running repair permissions:

Code: 
sudo diskutil repairpermissions /
 
When I called Applecare I discussed it with one of the techs. They said if you use the repair cd it will use the bom files from the cd instead of the hard drive.
 
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