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Re: Does Disk Utility's Repair Disk Permissions Do Anything?

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On 2013-10-26, Matthew Lybanon <lybanon@earthlink.net> wrote:
> Mac OS X 10.8.5.
>
> After installing several system updates I ran Disk Utility's Repair Disk 
> Permissions.  Because "Show details" gave a fairly long list of 
> (presumably) repairs, I ran it again, just to see what would happen.  It 
> found what I think is the same list of things to repair (I didn't check 
> every one, but it was a similarly long list and several items were 
> repeats of items in the first list), and again claimed to fix them.
>
> I know it looks like I've answered my own question, but I'd like to know 
> what other people think.

Disk Utility's Repair Permissions function isn't as magical a tool as a
lot of people seem to assume. It's a very simple tool that is meant to
reset the states of ownership and permissions of *specific sets of
files*, and *only* those files listed in the receipts of specific
software in the receipts folder. This receipts folder is located at
/Library/Receipts in Mac OS X versions prior to 10.6, and was moved to
/private/var/db/receipts starting with version 10.6.

Repair Permissions reads the contents of each receipt in the receipts
folder to find out which files and folders it should examine. Receipts
are typically created by software installers that use the Mac OS X
built-in /Applications/Utilities/Installer program to install a software
package, though they may be placed into the receipts folder by other
means as well. Receipts typically contain a "Bill of Materials" file
that lists of each important file and folder in the installed software
package, along with the expected ownership and permissions those files
and folders, according to the install package.

Repair Permissions examines only those files listed by these receipts.
This means the files in your home folder and the files in the local
domain (/Library for instance) are *not* examined. 

The Repair Permissions tool has a rather serious design flaw: it does
not know how to resolve cases where multiple receipts list the same file
or folder with differing ownership and permissions. This actually
happens fairly frequently, particularly when more than one software
package installs and uses a shared library or other system resource that
happens to be used by another software package. If there are multiple
receipts that list a given file or folder, and the expected ownership
and permissions differ between those two receipts, Repair Permissions
will encounter the first receipt, change the ownership and permissions
to honor that receipt, then encounter the second receipt and change the
ownership and permissions to honor the second receipt. This typically
manifests itself in Disk Utility's Repair Permissions log as a
file/folder that never seems to be actually repaired, flipping back and
forth between two states.

Once you understand how it works, you see Repair Permissions is not half
as useful or magical as a lot of people seem to believe. I wish more
people understood this - we probably wouldn't see so many Mac users
running Repair Permissions at the drop of the hat or on a regular
schedule as we see so often.  ; )

Bottom line: If you are not experiencing problems with a specific piece
of software listed in the receipts folder, there's no reason to run
Repair Permissions.

-- 
E-mail sent to this address may be devoured by my ravenous SPAM filter.
I often ignore posts from Google. Use a real news client instead.

JR

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Thread

Does Disk Utility's Repair Disk Permissions Do Anything? Matthew Lybanon <lybanon@earthlink.net> - 2013-10-26 13:25 -0500
  Re: Does Disk Utility's Repair Disk Permissions Do Anything? Lewis <g.kreme@gmail.com.dontsendmecopies> - 2013-10-26 19:35 +0000
  Re: Does Disk Utility's Repair Disk Permissions Do Anything? J Burns <burns4@nowhere.com> - 2013-10-26 18:35 -0400
  Re: Does Disk Utility's Repair Disk Permissions Do Anything? Alan Browne <alan.browne@FreelunchVideotron.ca> - 2013-10-26 19:03 -0400
    Re: Does Disk Utility's Repair Disk Permissions Do Anything? Your Name <YourName@YourISP.com> - 2013-10-27 12:22 +1300
      Re: Does Disk Utility's Repair Disk Permissions Do Anything? Alan Browne <alan.browne@FreelunchVideotron.ca> - 2013-10-26 20:24 -0400
    Re: Does Disk Utility's Repair Disk Permissions Do Anything? me@home.spamsucks.ca (Király) - 2013-10-27 20:10 +0000
      Re: Does Disk Utility's Repair Disk Permissions Do Anything? Jolly Roger <jollyroger@pobox.com> - 2013-10-27 21:38 +0000
      Re: Does Disk Utility's Repair Disk Permissions Do Anything? JF Mezei <jfmezei.spamnot@vaxination.ca> - 2013-10-27 19:00 -0400
  Re: Does Disk Utility's Repair Disk Permissions Do Anything? jamiekg@wizardling.geek.nz (Jamie Kahn Genet) - 2013-10-27 13:15 +1300
    Re: Does Disk Utility's Repair Disk Permissions Do Anything? Matthew Lybanon <lybanon@earthlink.net> - 2013-10-27 11:35 -0500
      Re: Does Disk Utility's Repair Disk Permissions Do Anything? J Burns <burns4@nowhere.com> - 2013-10-27 15:52 -0400
      Re: Does Disk Utility's Repair Disk Permissions Do Anything? Lewis <g.kreme@gmail.com.dontsendmecopies> - 2013-10-27 21:05 +0000
  Re: Does Disk Utility's Repair Disk Permissions Do Anything? Jolly Roger <jollyroger@pobox.com> - 2013-10-27 19:49 +0000

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