How to List Open Files and Processes in Ubuntu

This article explains how to identify open files and their associated processes on Ubuntu using the command line. It focuses on the primary utility designed for this task, providing essential syntax and common examples to help system administrators and users monitor system activity effectively.

The lsof Command

The command used to list open files and the processes that opened them is lsof, which stands for “List Open Files.” In Unix-like systems such as Ubuntu, everything is treated as a file, including network connections and hardware devices. Therefore, lsof provides a comprehensive view of system resources currently in use.

Basic Usage

To view all open files on your system, open the terminal and run the following command:

lsof

Because this generates a large amount of output, it is often helpful to filter the results.

Common Examples

List files opened by a specific user:

lsof -u username

List files opened by a specific process ID (PID):

lsof -p 1234

List network connections using a specific port:

lsof -i :80

List all network connections:

lsof -i

Using Sudo

Many system files and processes are owned by root and are not visible to standard users. To see a complete list of all open files on the system, prepend sudo to the command:

sudo lsof

This ensures you have the necessary permissions to inspect all active processes and file handles.