How can I tell if two files on different filesystems are the same?
The obvious way is to fetch a copy of one of the files onto the filesystem of the other and then use cmp or diff. However, that may be slow if the files are big, or impossible if the two filesystems are not connected by a network. Surprisingly, there is still a reliable way to tell if the files are the same: file checksums. With good checksum algorithms, the probability of two different files having the same checksum is vanishingly small: it would not happen by chance in the lifetime of the universe. It is common practice in announcements of new software releases to report such checksums, either in e-mail, or in small files distributed with the software. Our FTP archives at ftp://ftp.math.utah.edu/pub have such files, and as a further precaution, the software distributions are accompanied by digital signature files.
