Which command helps forensic investigators retrieve information about all active processes and open files?

The command that helps forensic investigators retrieve information about all active processes and open files is "lsof." This command stands for "list open files" and provides detailed information about files that are currently opened by processes. When executed, it generates a list of all open files, including regular files, directories, and network sockets, along with the associated processes that are using those files. This makes it an invaluable tool in digital forensics, as it provides insights into what is actively in use on a system at any given moment, allowing investigators to understand system activity and to identify potentially suspicious behavior.

The other options serve different purposes: "ps -ef" displays information about running processes but does not provide details on files they have open. "top" is a task manager that provides real-time system performance data and lists currently running processes but lacks detailed file usage insights. "htop" is an improved version of "top," featuring a more user-friendly interface and additional process management capabilities, yet it also does not show open files associated with processes. Therefore, while other commands can provide valuable information about processes, "lsof" specifically meets the needs of forensic investigations related to active processes and open files.