I'm trying to use FSKit to create a File System Extension that can read MFS-formatted disk images, following the old MFSLives sample project for reference. I have a well-formed MFS formatted img file that I'm trying to mount, but I'm having trouble getting the system to actually use my FSModule. DiskImageMounter fails to mount the img file, but I'm able to use it to attach the image as a device by clicking "Ignore" when it prompts me that it isn't able to read the disk. This is effectively the same as using the hdiutil command in Terminal. hdiutil attach -imagekey diskimage-class=CRawDiskImage -nomount Sample.img I've read that FSKit isn't fully integrated with Disk Arbitration yet, so I decided to see if I could force the system to use my extension by using the mount command. mkdir /tmp/Sample mount -F -t MFS disk54 /tmp/Sample Watching the logs in Console, I can see that fskit_agent sees my extension in its "New Modules List", and I see an MFS process gets launched and logs messages from com.apple.running and com.apple.xpc. However, the logs from the MFS process end there, and don't include any of my debug logs, which should be posted when my FSFileSystem subclass is created or when probeResource is called. Ultimately the mount command fails with exit code 69 and prints the following error message: mount: Probing resource: The operation couldn’t be completed. Permission denied mount: Unable to invoke task I've checked everything I could think of: The extension is enabled in System Settings. The extension has the FSKit Module capability added in Xcode. The Info.plist sets the FSSupportsBlockResources key to YES. The Info.plist sets both the FSName and FSShortName keys to MFS. The extension has its Team set to my developer account, with Xcode setting the Provisioning Profile and Signing Certificate automatically. The hosting app has its Team set to my developer account with the "Development" signing certificate. I wanted to see if it was something with my project configuration or implementation, so I downloaded the KhaosT/FSKitSample project from GitHub. Once I got that building, I tried mounting a disk image using the MyFS extesnion, but my system wouldn't run that either. Is there something about the system configuration I should be aware of to enable File System Extensions? I have my MFS extension showing up and enabled, but I'm not sure if there's something I'm missing that I still have to do. Is there a capability or signing requirement I didn't list that's required for the extension to run? The documentation doesn't specify anything about the entitlements, signing capabilities, or Info.plist keys, so I'm not sure what I should be looking for. I'm running macOS Sequoia 15.6.1 on an M2 Max MacBook Pro, and I'm building my project with Xcode 26 beta 6.