Which command is used to check disk usage of a filesystem?

The command used to check disk usage of a filesystem is "df". This command provides an overview of the amount of disk space used and available on filesystems. When executed, it displays results for all mounted filesystems, along with details such as total size, used space, available space, and the mount point of each filesystem.

"df" is particularly useful for quickly assessing how much disk space is utilized versus how much is free across various mounted filesystems, making it a valuable tool for system monitoring and management.

The other options serve different purposes: "du" specifically checks the disk usage of directories and files rather than entire filesystems, making it suitable for analyzing space usage for specific paths but not as a comprehensive overview of mounted filesystems. "lsblk" lists information about block devices and their mount points but does not provide direct statistics about disk usage. "free" is used to display memory usage information, providing an overview of system RAM and swap space rather than disk usage.