WhatsOpen
What's Open is a macOS utility that lists files currently in use so you can identify which app or user is preventing a disk from being ejected or unmounted.
What is WhatsOpen?
What's Open is a native macOS utility for checking which files are currently open across mounted volumes. It helps users find the app or user session that is keeping a disk, external drive, or other volume busy when macOS will not let it eject or unmount. This makes it useful for troubleshooting removable media, network volumes, and other storage devices that report they are still in use. The currently distributed version is maintained by Thomas Tempelmann, who provides a re-created 64-bit release for modern macOS versions and also offers older versions with some additional functions. What's Open is best suited to power users, support work, and everyday storage troubleshooting when you need a quick view of open file activity.
Key features
- List open files on mounted volumes
- Show which app or user is using a file
- Help identify why a disk cannot be ejected
- Assist with troubleshooting busy external or network volumes
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Safety overview
Status: Mostly safe
This is a legitimate troubleshooting utility for macOS storage and open-file activity. Its normal purpose is to inspect which apps or users currently have files open, so users should expect it to display file-use information relevant to mounted volumes. Keep in mind that closing apps or disconnecting storage based on its results can interrupt work if a file is still being used, so save changes before acting on what it reports.
Recommendation: Keep What's Open if you troubleshoot external drives, shared volumes, or stubborn eject problems on your Mac. If you do not use it, you can remove it without affecting macOS beyond losing this diagnostic tool.
Common paths
/Applications/What's Open.app
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