What's the "Private" directory in OS X for? I was running OmniDiskSweeper today, and I came across something called "Private" using 3.9GB. It is listed directly under the root directory along with Users, Library, System, and Applications, so I am assuming it is something included with OS X itself. I'm just curious about what this actually is, because I don't remember seeing this before. Here are some screenshots:







Mid 2012 15 inch MacBook Pro running OS X 10.11.3 El Capitan
/private has been around for a loooooong time. Every Mac has it.

It is part of your Mac: the directory stores essential system files and caches, along with other databases that your system requires to operate.



I'll give a quick explanation contents of the folders /private/etc, /private/tmp, and /private/var, usually found in /private:

/private/etc

Data files for system use, configurations for various command line tools etc

/private/tmp

System logs, mostly

/private/var

More logs, databases for daemons, virtual memory swap file(s), sleep image etc.



In essence, deleting anything in this directory is probably not a good idea, save for a few files. If you do delete them however, some required essential files will get regenerated on startup.

It's probably a good idea to Google the exact full directory path of any system folders you intend to tinker with before actually beginning to experiment with stuff inside.

I hope this helps.