The message target is busy means some process still has a file, directory, or working directory open on the filesystem you are trying to unmount.
Common causes
- A terminal is currently inside the mount point.
- A file manager has the directory open.
- An editor or media player still has a file open.
- A background process is scanning or indexing the filesystem.
Identify the process
fuser -vm /mount/point lsof +D /mount/point
Close the process cleanly where possible, then retry:
sudo umount /mount/point
If a process is stuck, terminate only the specific process you identified. Avoid using broad fuser -k commands without first checking what they will stop.