repair permissions a waste of time?

I read this and would like your thoughts, I have always repired permissions, but is it useless? please read the article, there is more, but the board software has a limited number of max characters
http://www.unsanity.org/

May 16, 2005
Exercises in Futility Part 2: Repairing Permissions is Useless
This is a rant I've wanted to write for an extremely long time. However, I prefer to let my anger/annoyance with some topics sit in the stew that is my soul and slowly boil until it is like you dropped a tea bag into a cup of very hot water housed in a smooth glass container that you just stuck in the microwave for 10 minutes. Yes, doing that will cause the water to spontaneously explode, leaving horrible burn marks all over your face (just be glad it wasn't maple syrup or something else that could stick to human flesh).

Update: Despite what Apple's Knowledge Base Article says, Repair Permissions does not repair permissions on any third party software (or any Apple software outside of the Base System). I just checked this by changing the permissions on FontAgent Pro and then repairing permissions. The permissions were not set to their correct values. This makes repairing permissions even more useless as it can't be used for any non-apple software. It also explains why installing CHUD or iPhoto from iLife '05 would cause the incorrect warnings to appear.

Now that that pleasantness is over with, the real issue I have is all these websites that suggest repairing permissions will actually fix/prevent problems. Even worse is when otherwise intelligent people are poised with a Mac OS X related troubleshooting problem and immediately suggest the user repair permissions. Repairing permissions won't fix your problem. As Jason Harris said (and I am paraphrasing), "Repairing permissions is zapping the PRAM for the twenty-first century". I couldn't agree more. Both are equally futile attempts to fix a completely unrelated problem. In other words, 99% of the time, neither will fix nor prevent any problem. Especially not the problems they are recommended for. People swear by repairing permissions as often as they save files and present as proof the fact they don't have any problems. That's rather specious reasoning. As with everything in life, The Simpsons has covered this topic well. Yes, I've shamelessly copied this text verbatim.

Homer: Not a bear in sight. The Bear Patrol must be working like a charm.
Lisa: That's specious reasoning, Dad.
Homer: Thank you, dear.
Lisa: By your logic I could claim that this rock keeps tigers away.
Homer: Oh, how does it work?
Lisa: It doesn't work.
Homer: Uh-huh.
Lisa: It's just a stupid rock.
Homer: Uh-huh.
Lisa: But I don't see any tigers around, do you?
[Homer thinks of this, then pulls out some money]
Homer: Lisa, I want to buy your rock.
[Lisa refuses at first, then takes the exchange]
Please ignore the fact that they're talking about tigers and Mac OS X version 10.4 just happens to be called "Tiger". The point stands. Just because something isn't around because you do something every day does not mean it would suddenly come around when you stop doing the something every day. Some people used to smear chicken blood all over their kin to keep the devils away too.

Call Me Lucy

I guess I should explain what repairing permissions is and isn't. Repairing permissions goes through all the Package files (.pkg) in /Library/Receipts/. A receipt package is created when (and only when) you install something using Installer.app (Apple's installer). First it creates a temporary package based on all the files in the package. Then when you install, it creates the actual package that actually contains a listing of all the files you installed from that package. You can see these two steps if you open Installer.app's Log window and choose "Show everything". The package lists the paths for all the files along with the permissions Installer.app set for them when they were installed (those permissions are part of the actual package in which the files were installed from). The items in /Library/Receipts/ are basically just the shell package without any of the actual files inside. You can see the contents of these by using the lsbom utility. The usage is basically lsbom path/to/archive.bom. Like so:

lsbom /Library/Receipts/MacOSX10.4.pkg/Contents/Archive.bom
This will list all the files that were installed by the package (by absolute path, usually), their installed permissions, file size, and some other information. See the man page for lsbom for more information on the output.

Anywho, when repairing permissions, the disk utility goes through the permissions of all the files in the target volume's /Library/Receipts/ folder. Apple has a kbase article on this as well. In order for the "repair permissions" or "verify permissions" button to show up, the target volume must have a version of Mac OS X installed on it. Repairing permissions only works on volumes that have a /Library/Receipts/ folder. Which is only there if OS X is installed on that volume.

Based on this information (and the sheer stupidity of Installer.app) you can correctly assume that Repair Permissions won't touch any files in any of the user's home folders since Installer.app can't target user folders specifically, only any folder or a specific path, and there are no packages in ~/Library/Receipts/. The only way it'd ever touch any files in a user's folder is if you installed something that let you explicity select a folder to install in (there are very few of those, none are available from Apple publically) and you chose a folder inside your user's folder. The receipt would still be installed in /Library/Receipts/ and it would only affect the user that installed it. It also won't fix permissions for any files that were created during the normal (or abnormal) use of OS X. This means it won't touch any cache files, database files, swap files, or settings files not created by the installer. If a file isn't listed in a receipt, it doesn't exist to the repair permissions process. It's really as simple as that. And because it reads from /Library/Receipts/ on the target disk, you can boot from a Mac OS X 10.2 CD and still use it to (correctly) repair permissions on a volume with Mac OS X 10.4.6 installed on it and it will set the permissions to the ones that 10.4.6 requires. There is no need for you to boot off a volume in order to fix its permissions.

A Bit of History

Does anyone actually remember when Apple first offered the ability to repair permissions and why it was needed? I do. Apple introduced the Repair Privileges Utility as a download for machines running Mac OS X 10.1.5. This was back in the long ago time when Macs would still boot Mac OS 9 and the default environment for a lot of Mac users was still Mac OS 9. Mac OS 9 didn't care about permissions at all. Mac OS 9 was Mac OS X's worst enemy in this area. If you booted into Mac OS 9 and ran some common applications, compressed and decompressed files, moved or renamed files, or (worse) ran a disk utility like Norton, they could completely destroy the permissions for many files that OS X needed to boot or run correctly. Since this was a relatively common occurrence and a huge support issue, Apple introduced the Repair Privileges Utility. When Mac OS X version 10.2 "Jaguar" came around, Apple rolled it into Disk Utility where it belonged. But by this time it wasn't needed nearly as much since many new Macs couldn't even boot Mac OS 9 thus rendering the fear of bad disk utilities that didn't pay attention to the rules set out by the HFS+ Technote ruining the ability to run OS X completely moot. Just because HFS+ didn't use the features when you wrote the disk utility doesn't mean it won't in the future (and the future is now, excluding named forks). None of this applies to using Classic as Classic lives in a mostly happy sandbox with just a trace amount of urine (which is more than I can say for my spacesuit).

The other number one cause of permissions going wonky were 3rd party installers that asked for root on OS X and changed permissions on some folders that were in the path to the destination. I know that MindVision and Allume (Courtney Cox-Arquette) have long since updated their installers to prevent this kind of weirdness (these would be the same installers that told you to quit all applications when installing software on OS X). I know there is always a chance I could be wrong about things like this so I've been running Repair Permissions after every install using these two installers just to make sure, and I haven't seen it note anything at all. So these two companies' installers are good. So this cause is also deemed completely moot.

The final minor cause for incorrect permissions is, basically, the user. I've said it before, and I'll say it again, you can't account for stupidity. People that change permissions on something because they think it might fix a problem they're having because they know more than the system but it very obviously won't fix the problem. More on this reason later.

The Ugly

Permissions won't magically go bad. They won't break suddenly. They don't suffer from bit rot. In order for permissions to change something must change them. Even with Mac OS 9, as long as you didn't modify the files, their permissions wouldn't change. For this reason, repairing permissions as a maintenance task is just a complete waste of time. Granted, it won't harm anything, but it won't help anything either. If you want to be paranoid about permissions then at least use some common sense when doing it and only run repair permissions after using an installer. I am not recommending doing it after using an installer, however.

Posted by rosyna at 02:15 PM | Comments (66) | TrackBack (3

I have heard this a couple of times, but then I have heard the same people come back later and say.. ok repair permissions.. i still feel like it's a waste of time, but you should probably do it..

I agree.. i think some people do it way too much, but I do it right before a backup and/or update.. then I do the backup and/or update, then after it's done. I reboot and then do another repair permissions. That's the only time I do it and I have no problems whatsoever.

It can't hurt, but it's definitely not the cure all that some people think it is.

i never do it, like it says permissions wont suddenly change so i dont bother. i didnt even do it before upgrading to Tiger so what reason have i got for doing it?

I think that repair permissions is a bit like in winblows with a reboot

I like the comparison to zapping the PRAM.

In the Olden Days, troubleshooting a Mac beyond a certain point (after you were satisfied an extensions conflict was not to blame) became a matter of voodoo and shotgun techniques. Permissions repairs continue that tradition.

I've never followed this, either. Why would Apple spend so much time and energy making a computer that the user doesn't have to worry about, only to require you to "repair permissions" every couple of days? It's senseless. Macs are designed to look after themselves.