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First advice if software-problems occur: "repair permissions. No .. repair them even if you have no trouble!" Well I do, and there is always something to repair. It's no big deal, but what the heck is constantly doing damage to my permissions? How is it possible that some "guerilla"-bits and -bytes can brake permissions in "todays most advanced OS"?
More than one application may access or share a directory, once in a while an application may change a directory, the other app may lose tack or access causing an error (the symbolic links between app and dir. become broken)
Repair Permissions is a verification program that fixes this and some other stuff.I don't think its an OS problem that causes this I think its an app data base thing.The more apps. you un/install, the more directories you create and move around the more you should repair Permissions.
To put it simply
I just makes sure your app. knows where all its directories are.
Actually, repair permissions only affects files and directories that are listed in a catalog. For each of the files/directories in this catalog (the catalog contains only Apple's OS stuff I believe*), it compares owner/group and permissions with the current owner/group and permissions. If the current owner/group permissions are different, it sets them back to what's in the catalog.
As far as how owner/group for files/directories and the permissions for these are changed:
1. Users can change then e.g.:
chmod -R 666 /
would change permissions for everything on your system (that you have permission to change) to 666 (owner, group, and others have read and write access, which would pretty much break your system...).
2. Application installations can change permissions and owner/group of files and directories. When you provide a password with admin privs when an installer requests it, you're basically giving the installer privileges to change whatever it wants during the course of the installation.
* Now, I'm also unclear about the contents and the location of this catalog. I've heard from others that any app that uses the standard Apple OSX install facilities can upgrade the catalog. I've also heard that this isn't true and that only Apple updates the catalog when you upgrade the OS (e.g. from 10.3.6 to 10.3.7) so would very much be interested in the truth from someone that knows (a reference link would be wonderful).
This link from Apple answered my questions regarding where the "catalog" is stored and what, specifically, is fixed when repair permissions is run.
From the link.
If you have modified the contents of the folder /Library/Receipts, the Repair Permissions feature won't work as expected. Repairing permissions requires receipts for Apple-installed software. Additionally, the utilities only repair Apple-installed software and folders (which does not include users' home folders).
Although this other link from Apple seems to imply that ANY package that places a .pkg file in /Library/Receipts will benefit from Repair Permissions since it says:
When you use Disk Utility to verify or repair disk permissions, it reviews each of the .bom files in /Library/Receipts/ and compares its list to the actual permissions on each file listed.
I checked in /Library/Receipts and see several non-Apple packages there. So, I'm guessing that these will be checked and corrected by Repair Permissions as well.
