SHA256 is a cryptographic hash function in the SHA2 family. It takes an arbitrary amount of data and maps it to 512 bits.
It’s often used to validate the integrity of large or important data
intended to be transfered over a network. For example, Linux and BSD ISO
download pages often include a SHA checksum which you can use to verify that downloaded the complete file without any corruption. If the SHA’d value of your downloaded file is the same as the provided checksum, you can be sure it matches the file on the server.
OSX includes a program called
shasum that can be used
to compute the SHA256 (and SHA 1, 224, 384, and 512) hash of a file.
shasum uses SHA1, but it can be used for SHA256
shasum -a 256 example.txt
On Linux: Linux includes a suite of tools for calculating SHA checksums named after the hashes they computer. They are sha1sum, sha224sum, sha256sum, sha384sum, and sha512sum. The shasum program mentioned above for OSX is also available on Linux.
To calculate the SHA256 hash of a file named “example.txt”, run: