Md5sum

Content sourced from Wikipedia, licensed under CC BY-SA 3.0.

Md5sum is a small program that creates and checks 128-bit MD5 hashes for files. An MD5 hash is like a fingerprint of a file: if the file changes, the hash usually changes. MD5 is fast, but it’s no longer considered secure. Don’t rely on it for security purposes; for verification against tampering, use a newer hash like sha256sum.

Md5sum is commonly used to verify file integrity after a transfer or storage, by comparing the current hash with a saved one. It’s included in most Unix-like systems as part of GNU coreutils or compatible tools like BusyBox. The original C code was written by Ulrich Drepper and came from glibc in 2001. When you run md5sum, you typically get lines with a hash and a filename.

Note: on FreeBSD and OpenBSD, the utilities have slightly different names (md5, sha1, sha256, sha512) and options. FreeBSD also offers other digests such as SKEIN.