When trying to unmount a device it is reported as being busy. Which of the following commands could be used to determine which process is causing this?

`debug` is a general term for troubleshooting and not a specific command to list open files.

The `lsof` (list open files) command identifies all open files and the processes that currently have them open. When a device cannot be unmounted due to being "busy," `lsof` can pinpoint exactly which process is accessing files or directories on that device, thus preventing its unmount.

`nessus` is a vulnerability scanner, not a tool for checking open files.

`strace` is used to trace system calls and signals, not to list open files.

`traceroute` is used to trace the path of network packets, not to identify processes holding files open.