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A file can be “summarized” into a short string. That string can be compared with the file again to determine if it’s the same file. This is often used when downloading a file to check it after the fact. This sort of thing is built into compression software, but using md5sum is way faster/easier because it doesn’t need to put the file in a container and uncompress it to use it.

There are various other programs which do similar things, like sha256sum. These all come with almost all Linux distributions.

Checking a file, using a filename ∞

Is your ISO ok? If you don’t know, do this:

md5sum -c $MD5_FILENAME

-c for md5 on NetBSD 3.0 ∞

The md5 command in NetBSD 3.0 does not support the -c option for automatically checking MD5 sums. The following script will allow you to automatically check MD5 sums.

See md5-dash-c-on-netbsd-3.0.sh

Alternatives ∞

• cfv

  • Tests/creates .sfv, .csv, .crc, .md5(sfv-like), md5sum, bsd md5, sha1sum, and .torrent files.
  • I prefer this.