lsofs

lsof, which stands for "list open files," is a command-line utility that displays information about files opened by processes. It is a powerful diagnostic tool for system administrators and developers, helping to identify which processes are using specific files, directories, network sockets, or devices. The output of lsof can be filtered by various criteria, including process ID (PID), user, file name, and network port.

When a program accesses a file, directory, socket, or other resource on a Unix-like operating system, that resource is considered "open" by the process. lsof provides a snapshot of all currently open files. Each line of output typically includes the command name, the process ID, the user running the process, the file descriptor number, the type of file (e.g., regular file, directory, socket), and the name of the file or resource.

Common use cases for lsof include troubleshooting "resource busy" errors, identifying which process is holding a lock on a file, determining which process is listening on a specific network port, and tracking down deleted files that are still being held open by a process, preventing their deallocation. Understanding the output of lsof is crucial for effective system administration and debugging.