A friend who owns an OSX machine gave me a USB Drive that had some files on it.

In addition to the files in the folder, for each file there was a file with a duplicate name, except they had the prefix ._ and they are each 4kb.

What are these files, why are they created, and can they be safely deleted?

  • Possible duplicate of this and this, as well as this apple.se question. But the answers that say it's resource forks are only partly right -- the files contain all sorts of mac-OS-specific metadata, not just resource forks. – Gordon Davisson Jul 2 '19 at 3:18

What are these files, why are they created?

Answered on Ask Different SE: Why are dot underscore ._ files created, and how can I avoid them?

They're created to store file information that would otherwise go into an extended attribute on HFS+ (Apple native) or Unix/UFS volumes; in earlier Mac OS this would be the resource fork. Finder file operations will create them automatically to store the icon information, plus Time Machine stores some information in them so if you copy a file backed up via TM it will have that information copied as well.

Can they be safely deleted?

If you don't care about metadata the files may hold, then yes.

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