lsof
lsof (list open files) is a command-line utility for Unix-like operating systems that displays information about files opened by processes. It can list all open files, including regular files, directories, network sockets, and device files, along with details like the process ID, user, and file descriptor. This tool is essential for system administration, debugging, and security analysis to monitor and manage system resources.
Developers should learn lsof for troubleshooting issues related to file access, network connections, or resource leaks in applications, especially in server environments. It is particularly useful for identifying which processes are using specific files or ports, diagnosing 'file in use' errors, and detecting unauthorized network activity or security breaches.