The md5sum command is a tool that allows you to calculate and check the MD5 (Message Digest Algorithm 5) sum value of files. MD5 is a one-way hash function that produces a fixed-length 128-bit (32 hexadecimal characters) digest from an input string. This hash is often used to verify the integrity of files, since even a small change in the file results in a completely different hash value. In this tutorial, we'll cover the basic usage of the md5sum command on a Debian system.