sum calculates and displays a 16-bit checksum for the named file and displays the size of the file in kilobytes. It is typically used to look for bad spots, or to validate a file communicated over some transmission line. The checksum is calculated by an algorithm which may yield different results on machines with 16-bit ints and machines with 32-bit ints, so it cannot always be used to validate that a file has been transferred between machines with different-sized ints.

See largefile(5) for the description of the behavior of sum when encountering files greater than or equal to 2 Gbyte ( 2³¹ bytes).

See attributes(5) for descriptions of the following attributes:

sum(1), wc(1), attributes(5), largefile(5)

Read error is indistinguishable from EOF on most devices; check the block count.

sum and /usr/bin/sum (see sum(1)) return different checksums.

This utility is obsolete.