Transmac: Drive Has Been Locked By Another Program

At its core, the “locked drive” error is a manifestation of Windows’ volume locking mechanism. When an operating system accesses a storage device, it typically requests exclusive lock privileges to prevent data corruption. A locked volume cannot be written to or dismounted by a second program. Transmac, which requires direct, raw access to a drive’s sectors to modify HFS/APFS structures, requests this exclusive lock before performing any operation. The error appears when Windows denies this request, meaning another process—often invisible to the user—holds the key.

For persistent locks, advanced measures are required. The user can open an and use the mountvol command with the drive’s volume GUID to dismount the volume without a drive letter. Alternatively, the diskpart utility allows the user to select the disk and use the offline disk command, which forcibly resets the lock state. A final nuclear option involves disabling the “Automount” feature in Windows via mountvol /N and rebooting, preventing Windows from automatically claiming newly attached drives before Transmac can access them. drive has been locked by another program transmac

Prevention is superior to cure. Users should adopt a workflow that minimizes lock conflicts: always eject the drive from macOS properly, avoid opening the drive in File Explorer before launching Transmac, and temporarily disable real-time antivirus scanning for external HFS/APFS drives. Some advanced users dedicate a USB port exclusively for Transmac operations, preventing other services from polling the drive. At its core, the “locked drive” error is