Xcode glossary

What is ~/Library/Developer/CoreDevice/DeviceFS, and why does it look like 100+ GB?

By MD Kadiwal · Updated October 3, 2026

Quick answer

It's not using your disk. ~/Library/Developer/CoreDevice/DeviceFS is a virtual file system that macOS mounts to show the files of simulators that are running. Tools that walk folders, like du or disk visualizers, count those files again and can report 100 GB or more, but df shows the mount uses 0 bytes. Don't delete it; it isn't real data.

What we found

On our test Mac, du reported 120 GB in ~/Library/Developer/CoreDevice, more than all of Xcode's real data combined. Looking closer:

mount lists DeviceFS as its own file system (type devicefs), mounted from the com.apple.CoreDevice.CoreDeviceService container.
df reports that file system as 0 bytes used.
It held one folder per running simulator (device-<UDID>.localized), matching xcrun simctl list devices booted, each with AppDataContainers, AppGroupContainers and the simulator's root file system.

So it's a window onto the simulators' files, which already live in ~/Library/Developer/CoreSimulator and in the simulator runtime disk images. Counting it adds the same files a second time.

Check it on your Mac

mount | grep DeviceFS
df -h ~/Library/Developer/CoreDevice/DeviceFS
xcrun simctl list devices booted

Can I delete it?

No, and there's nothing to gain. It doesn't take space. To reclaim the space the simulators really use, delete simulators or runtimes you don't need (see deleting simulator runtimes).

Questions

Why does DaisyDisk or du show CoreDevice as huge?

They walk into the mounted DeviceFS and count each running simulator's files again. The mount itself uses no disk space.

Will it go away?

On our Mac it showed one folder per running simulator. Shutting simulators down is the normal way to make them stop appearing there.