Checksums are used verify data integrity and in some cases, authenticity.
It is especially important to run checksums on large files, such as operating systems, where 100% completeness is desired. As file size increases, so will the possibility of errors during transmission.
To check a single file on Mac OS X, simply run:
shasum -a 256 file.iso
To check multiple files using a SHA256SUMS file:
cd ~/Downloads shasum -a 256 -c 1.4.3_SHA256SUMS 2>&1 | grep OK
If the file was verified you should see: