You can receive “device is busy” error when you want to unmount a mount point in Linux operating system.
For unmount operation, you may want to read the article titled “How To Mount and Unmount Zfs Mount Points on Exadata“.
Find the Cause of the Error
If you receive this error during the unmount operation, you can find the operation that caused this error using the following command.
lsof | grep /zfs/test
As you can see in the screenshot below, you can kill the process that caused the device is busy error.
kill -9 xxxxxx
Before you kill the process, it will be more accurate to find the owner of the process and ask him/her to kill the process. Because when you run the kill command, it will end the process of the user. This can cause undesirable consequences.
If this does not solve the problem, you can unmount the mount point using the below command.
-l means lazy and the mount point is unmounted regardless of who uses this mount point.