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December 11, 2007

geekery

Don’t worry so much about Repair Permissions

Posted Dec. 11, ’07, 6:31 AM PT by Derik DeLong
Category | Geekery

Repair Permissions Most Windows transplants ask upon switching about what maintenance they need to do. The most resounding, oft-repeated responses is Repair Permissions. This little part of Disk Utility is hailed as the solution to all problems. Kernel panics? Repair Permissions. Application crashes? Repair Permissions. Slow internet? Repair Permissions.

The problem is that rarely can one of these advisors explain what it does, or how. Even worse, they have no explanation for the messages that will come out of the utility on a regular basis. Apple to the rescue, finally. In that knowledge base article, Apple notes that specific SUID system files have been modified and won’t be repaired. The message never goes away, confusing novice users that are regularly directed to the utility (and subsequently waste a lot of time, thinking that’s the cause of all their problems).

I’m not saying the utility is without use, but some of its output is utterly meaningless.


10 Comments

Ken said:

For the curious, Apple does actually have a knowledge base entry about what repair permissions does:

http://docs.info.apple.com/article.html?artnum=25751

December 11, 2007 8:12 AM
PFV said:

Repairing permissions clears up my unused (but inaccessible) memory. I need to restart the computer or repair permissions daily or else my computer slows terribly.

One question to demonstrate my ignorance: What are permissions, and why do they need to be repaired?

December 11, 2007 8:27 AM
Nick said:

"What are permissions ...?"

They govern who can read, write, or execute/have access to what. Have a read of this article:

http://www.dartmouth.edu/~rc/help/faq/permissions.html

"why do they need to be repaired?"

You must be running Tiger. On Leopard, Disk Utility has text on it explaining what the functionality is for. It says:

"If you are having permissions problems with a file installed by the Mac OS X installer, click Repair Permissions".

In other words, some badly behaved applications that use the OS X installer change the permissions on directories on installation. A better name for the functionality might be "Reset Permissions" (i.e. to factory defaults). A sysadmin might deliberately want to set permissions on something differently to factory defaults. So "repair" is a misnomer here.

What Apple says is the use for that functionality and nothing else. Obviously, if some application is trying to run some process and lacks permission to access some directory (folder) that it needs to access - because permissions on that directory have been changed - it'll break. Hence the need to reset the permissions.

If permissions are too tight, stuff can break; but equally, you don't want permissions too lax because that's a security hazard. But there's not much point in resetting - "repairing" - permissions, unless you know you have a problem that is caused by "wrong" permissions. In any case, Disk Utility only looks at a small subset of all the files and folders on your machine: the ones installed by the Apple installer. You could have a permissions problem that Disk Utility didn't know about and wouldn't touch.

December 11, 2007 10:01 AM
michael said:

PFV, that’s just voodoo. My Mac is running for weeks without a reboot and I never noticed any (significant) slowdowns. Number of times I have repaired permissions since I have a Mac (1.5 years): Zero.

It does not at all clear up memory. It has nothing at all to do with your memory. It doesn’t even touch your memory.

The only case in which you should repair permissions is when you have problems with permissions. And that will most likely only ever happen if you manually diddle around with permissions of program or system files. Which you normally will never ever do.

Repairing permissions is a very strange Mac cargo cult.

December 11, 2007 10:29 AM
Mark Issacs said:

I've been told (since the transition to OS X) that the Unix file ownerships and who can read/write/modify various system files is VERY important and these things do get somewhat scrambled. I've always been told that Repair Permissions needs to be run before and after major upgrades to insure smooth problem free installations. I've followed this advice religiously and have never had a major system problem to date, even though I've been upgrading this system since the days of OS 10.2. I'm up to 10.4.9.? now and still running fine. As I make the Leap to Leopard I may do a clean install to get the old dead wood out of the system files, etc. But then again, maybe that will end up being far more hassle than it's worth. Time will tell. Any ideas if I should do a squeaky clean new install of Leopard on my HD and then use Migration Assistant to move over the apps and their related files? I hat to do it manually because there's so much that is hidden from view and easily missed.


December 11, 2007 3:14 PM
PPV said:

Michael: "PFV, that’s just voodoo." Well I guess I'm beginning to believe in the magic.

Right now, 12 hours after a restart, my memory use is as follows:
328 used
143 wired
650 inactive
579 Free
Pageins 160k pageouts 20k
After a few more hours of use, the free memory will be close to 0 and I will have significant slowdowns, especially working in video.

After quitting my programs and repairing permissions, my free memory stands at 1.2g. No more slowdowns are evident in video.

If you can explain the "voodoo" I'd greatly appreciate it. I know several people who have this problem, which they refer to as a "memory leak." All I know is that it sucks.

December 12, 2007 6:48 AM
michael said:

Inactive is just as good as free. Even if Free comes close to zero (which will happen) you don’t have to worry, as long as Inactive is high enough (Inactive means basically “previously used, but now no more needed by the app, aka free”.) The low value of Free memory kept me up at night (and I, too, experienced perceived slowdowns) until I was finally told that the value of Inactive memory is also important.

Certainly at some point your apps gonna eat up more and more memory, so quitting them surely helps a lot. Repairing permissions in that context is just a cargo cult. Don’t do that anymore and you will be fine.

When you want to use your Mac for as long as possible I would just recommend to keep the number of apps you have running low. And if you experience slowdowns don’t reboot or repair permissions, just quit one app or two. Works for me.

December 12, 2007 8:22 AM
Paul said:

"After quitting my programs and repairing permissions, my free memory stands at 1.2g."

Michael is absolutely right. It's quitting your programs that frees up the the memory.

Watch out for your used + wired memory for total RAM in use. And watch your page outs. When that gets high, you're running out of available memory. And you don't say what apps you're using. Watch your usage while you open your apps and see what one pushes the usage up.

You may indeed need to install more RAM, but the figures you give are just fine. What are they like when you have slowdowns?

My TV-connected Mini has only 512MB RAM and its Page outs stands at 3.5GB after four weeks or so since the last reboot (when I put Leopard on it). I really need to add more RAM, but I only see it slowing down when I run XP in VMWare Fusion to use Netflix Watch Instantly. But since I usually only run Front Row on it it works fine.

December 12, 2007 9:53 AM
michael said:

Yep, VMWare Fusion really slows down my MBP (with 2 Gigs even). Anything else pretty much not. Although I’m not really running much demanding stuff.

December 12, 2007 12:09 PM
PPV said:

Thanks for all the advice. Let me explain my confusion.

I'm using MainMenu to monitor my memory use. After a day of work, I'm almost out of "free memory" as indicated in the "Memory Pages" section of MainMenu. Unused memory takes up most of the memory. I quit all my programs -- inactive is still almost 750MB -- and start PowerPoint for a presentation that includes imbedded Quicktime video. The video sputters. I quit all my programs I repair permissions -- inactive memory is cleared -- PowerPoint works without a hitch.

I'm have a 15" PowerBook 1.5GHz with 1.5GB of ram.

I can't figure it out, but I have talked with others who have the same issue.

December 12, 2007 3:00 PM

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