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In OS X there is a lock icon in the lower right of the Get Info screen. What is this icon called? What does clicking this icon do?

I am running on an account with administrator access. I have the ability to change permissions of some folders (one on my desktop) but not others (one in the Applications folder). The "lock" is locked in both cases. When I tried to Terminal → su → chmod the folder in Applications I still had no luck, until I pressed the 'lock' button.

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Clicking the lock icon will prompt you for an admin password. After you provide it, the system will allow you to change the permissions for that file or folder in that "Sharing & Permissions" pane you see at the bottom of the Get Info window. This is a feature of the underlying Unix operating system that allows different privileges for a user, group, and others.

Note that you are always allowed to change permissions (whether the icon is locked or unlocked) when you (your user) is the owner of the file -- e.g. most of the files in your own user folder such as your Desktop and Documents folders. But when you are not the owner, you'll have to unlock this option to change the permissions.

There's a reason this feature is "locked" against casual access. It's not really something you want to touch if you're not very sure what you're doing. Messing with permissions can cause access problems, security problems, or both.

For more details, check out this Wikipedia article: http://en.wikipedia.org/wiki/Filesystem_permissions#Traditional_Unix_permissions

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    Oddly, it looks like this icon appears (and is active) whether or not you already have permission to modify the sharing/permission on the file. – jhfrontz Mar 10 '16 at 17:37
  • Except I can change the individual privileges for each group (me, staff, everyone) between read-only and read/write, and the lock icon doesn't change… and I can toggle the lock icon open and closed, and the privileges don't change—I see no correlation. – jtheletter Apr 13 '18 at 5:24
  • @jtheletter The "lock" there doesn't in itself change any permissions. It is only enabling or disabling the ability to change the permissions in that dialog window. Apple has this "lock" on there so users won't make accidental changes to file/folder permissions which could be harmful. (Most regular users will never need to change these permissions, and most system admins and power users who need to will do so via the command line.) It also provides security against an unauthorized individual walking up to a logged-in mac and tampering with permissions for nefarious purposes. – Austin Apr 20 '18 at 1:53
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    @jtheletter Yes, you are always allowed to change permissions when your user is the owner of the file. For an example of files you don't own, try almost anything outside your own user folder, e.g. /System/Library/Sounds/... (but don't actually change the permissions). Hope that clears it up. – Austin Apr 20 '18 at 20:49
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    @jtheletter I hadn't mentioned it because the original question mentioned that they were able to change permissions for their own files but not others. But I added a clarification to my answer for future visitors. Cheers! – Austin Apr 22 '18 at 6:50

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