[Phoenix]

Ok this is probably a stupid question but im fairly new on the whole mac thing. I dont understand permissions....... ive tried reading about it but all it basically tells me is how to reset them etc. Not what they are, what they do, etc. Any help from anyone? thanks

[drewprops]

One of the smarter guys is going to really explain this to you better, but file permissions essentially declare who can read and write to a file. There are three types of people who may have permissions, the Owner, the Group and Others. The three types of accessibility a file can have is No Access, Read Only and Read/Write. When you work in an environment where you may have sensitive files exposed to inexperienced users those files (or directories (known better as folders to most people)) are often issued No Access permissions and only a "super administrator" can change those settings.

There are approximately fifty kajillion files in the BSD 'nix core under OS X and eventually, with all those files moving around, something gets tweaked the wrong way.. the persmissions can get whammied. When you "repair" permissions the Disk Repair resets permissions to files to what they should actually be.

That's the layman version... guys?

[Phoenix]

so why is it necessary to reset them?

[SonOfSylvanus]

Originally Posted by trav so why is it necessary to reset them?

Originally Posted by drewprops There are approximately fifty kajillion files in the BSD 'nix core under OS X and eventually, with all those files moving around, something gets tweaked the wrong way.. the persmissions can get whammied...

When the permissions get "whammied", everyday applications, like Safari, Mail, iTunes etc can stop working properly or not work at all.

"Repairing Permissions", is a way of resetting the system to a former "pristine" state—it lets all the different parts of your Mac communicate with each other as they should and is the first port of call when troubleshooting.



/NOT one of the smarter guys

[adam_tj]

Basically, drewpops, that explanation is pretty good. It's just so inexpierenced users cannot edit system files. If you've ever had anyone rename C:/Windows/ as
C:/Doors/, then you know why this is the greatest feature of Unix-based OS'es.

[boris]

I understand "owner" permissions, and I sort of understand "system" permissions, but what about these groups? When setting permissions, the OS gives you quite a selection (in the popup) of groups to choose from, or you could name your own. What are the groups for? Is there a description of what each of the many suggested groups are for? OSX help was of little help with my question.

Thanks,

Boris

[Brad]

Ah, explaining the permissions system. One of my specialties.

Mac OS X follows the same basic permissions system that nearly all other versions of Unix and Linux use. Windows has a loosely related permissions system, but it's hidden away and obfuscated under layers of bad UI.

Every file and folder in Mac OS X has nine basic attributes. (Yes, experts will clamor that there are actually more, but I'm sticking to the basics here!) There are three settings for three user categories. The user categories are:

• owner
• group
• everyone

And the three settings for each of these are:

• writable
• readable
• executable

These are all very important for security reasons. For example, your Documents folder is readable by you (the owner) but not by anyone else! Of course, you can imagine all sorts of combinations. You can have things that you can read and write but others can only read (like protecting shared documents), things that are writable but not readable by everyone else (like a drop box), etc.

But, what's up with the "group" category? That's so you can apply special permissions to more than just one specific user. For example, the Applications folder on Mac OS X, by default, is not writable by the "everyone" category. This protects unauthorized users or malicious software from changing or damaging applications. So, how can you add software if the "everyone" category is forbidden? Simple! Set the permissions for that folder to allow the group "admin" to have writable access. This way, only users that the system knows are in the admin group can modify its contents.

The vast majority of people will never make changes to permissions in the group category. They'll usually just change the global "everyone" settings and their own personal "owner" settings because setting up new usergroups can be cumbersome (and there's no good GUI for it).

If you want to check out some permissions, select a file or folder on your drive in the Finder and press command-i (or choose Get Info from the File menu or control-click the file and choose Get Info). See the little disclosure triangle by "Ownership & Permissions"? You can expand that and see some of the gory details. That window provides a slightly simplified approach, combining some options and leaving out others (namely the executable bit).

What's this business about repairing permissions?

Well, this is a subject that has a lot of myth behind it. Many users fall back to "repairing permissions" as a catch-all fix for when things act weird in Mac OS X. Indeed, it's even listed in our FAQ thread as a step in routine maintenance. Borked permissions can prevent programs from running, deny you from accessing certain things, or cause odd behaviors in running applications if they are denied access to support files they need.

In short, repairing permissions checks the system's known default settings for certain files and folders, scans those files, and corrects the permissions on them according to the known default values.

Is this a necessary routine to carry out, though? No, not really. It's quite rare for permissions to get mangled. Usually it's because of two things: user error (somebody accidentally manually changed the wrong permissions) or an installer crashing, hanging, or quitting before it has completed applying the correct permissions. There's also the case of the occasional installer that sets the wrong permissions on something because the developer was an idiot. Fortunately, these are few and far between since very little software on Mac OS X actually uses an installer mechanism.

Hope this helps.