What does the 'df' command show in Linux?

The 'df' command in Linux is used to display information about disk space usage on the file system. Specifically, it reports the amount of disk space used and available on all mounted file systems. When you run the command, it provides details such as the total size of the file systems, how much space is currently utilized, how much is free, and the percentage of disk usage. This is particularly useful for monitoring disk space to ensure that there is sufficient storage available for files and applications.

The other options relate to different functionalities: memory usage involves commands like 'free' or 'vmstat', the current directory can be shown using the 'pwd' command, and process status is typically displayed by commands like 'ps' or 'top'. Thus, the primary purpose of the 'df' command is centered around disk file system usage, confirming that the correct answer is indeed related to this function.