What does the 'df' command do?

The 'df' command is used in Linux and Unix-like operating systems to report on the disk space usage of file systems. When executed, it provides information on the available and used disk space for mounted file systems. This command is particularly helpful for system administrators and users to monitor how much disk space is being utilized and how much is still free, enabling them to manage storage resources effectively.

In the context of the provided options, this functionality aligns perfectly with the description of reporting file system disk space usage. Understanding disk space is crucial for maintaining system performance and preventing issues related to insufficient storage.