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While holding Opt and Shift, the Finder menu items Duplicate and Paste Item become Duplicate Exactly and Paste Item Exactly. These require administrator permissions.

How are they different from the regular commands?

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up vote 11 down vote accepted

When duplicating or pasting a file, the new file isn't exactly like the original. While it has the same contents, modification date, permissions, and extended attributes, it lacks the original's ownership information: You are the owner of the file you create!

Especially when changing system-wide configuration files, or doing administrative tasks using other users' files, it's important to mind the permissions, otherwise some services refuse to work, or the other user accounts might no longer be able to access or edit the files.

Duplicate Exactly and Paste Item Exactly preserves the original's basic ownership information (user and group). This isn't usually possible, and require administrative permissions to perform. It's an easy way to make temporary backups with correct original permissions before replacing system files.

Access control lists aren't preserved though, even when using the … Exactly commands.

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Good answer. I would like to see some references though. – chharvey Nov 30 '15 at 3:48

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