Which of the following commands would you use to display disk space usage?

The command used to display disk space usage is 'df', which stands for disk filesystem. When executed, it provides a summary of available and used disk space on all mounted filesystems. This includes information such as total filesystem size, used space, available space, and the percentage of space used, which is useful for system administrators to monitor disk usage and ensure that filesystems do not run out of space.

Although 'du' is also related and provides disk usage information, it is typically used to estimate file space usage for specific directories and files, rather than giving an overview of all mounted filesystems. The 'free' command is used to display memory usage, while 'lsblk' lists information about block devices but does not directly show the amount of disk space used or available.

Thus, the 'df' command is the most appropriate choice for displaying overall disk space usage, making it the correct answer.