sum is a legacy utility available on someUnix andUnix-likeoperating systems. This utility outputs a 16-bitchecksum of each argumentfile, as well as the number ofblocks they take on disk.^[1] Two different checksum algorithms are in use. POSIX abandonedsum in favor ofcksum.

Thesum program is generally only useful for historical interest. It is not part of POSIX. Two algorithms are typically available: aBSD checksum and aSYSV checksum. Both are weaker than the already weak 32-bit CRC used bycksum.^[2]

Thedefault algorithm on FreeBSD and GNU implementations is the BSD checksum. Switching between the two algorithms is done via command line options.^[2][1]

The two commonly used algorithms are as follows.

The BSD sum, -r in GNU sum and -o1 in FreeBSD cksum:

• Initialize checksum to 0
• For each byte of the input stream
  • Perform 16-bit bitwise right rotation by 1 bit on the checksum
  • Add the byte to the checksum, and apply modulo 2 ^ 16 to the result, thereby keeping it within 16 bits
• The result is a 16-bit checksum

The above algorithm appeared inSeventh Edition Unix.

The System V sum, -s in GNU sum and -o2 in FreeBSD cksum:

• checksum0 = sum of all bytes of the input stream modulo 2 ^ 32
• checksum1 = checksum0 modulo 2 ^ 16 + checksum0 / 2 ^ 16
• checksum = checksum1 modulo 2 ^16 + checksum1 / 2 ^ 16
• The result is a 16-bit checksum calculated from the initial 32-bit plain byte sum

Thesum utility is invoked from thecommand line according to the following syntax:

sum [OPTION]... [FILE]...

with the possible option parameters being:

• -r
  • useBSD checksum algorithm, use 1K blocks (defeats-s)
• -s,--sysv
  • useSYSV checksum algorithm, use 512 bytes blocks
• --help
  • display the help screen and exit
• --version
  • output version information and exit

When no file parameter is given, or when FILE is-, thestandard input is used as input file.

Example of use:

$echoHello>testfile$sumtestfile36978     1

Example of -s use in GNU sum:

$echoHello>testfile$sum-stestfile510 1 testfile

Example of using standard input, -r and printf to avoid newline:

$printfHello|sum-r08401     1

• GNU Core Utilities
• UnxUtils port to native Win32

• sum in The Single UNIX ® Specification, Version 2, 1997, opengroup.org – does not specify checksum algorithm
• C.4 Utilities in The Open Group Base Specifications Issue 7, 2018 edition, opengroup.org – indicates sum as removed
• sum(1) – Version 7 Unix Programmer'sManual
• sum(1) – manual pages fromGNUcoreutils
• sum(1) – FreeBSD General CommandsManual – states the sum algorithms in options -o1 and -o2 to cksum
• sum(1) – Linux UserManual – User Commands from Manned.org
• sum(1) – Solaris 11.4 User Commands ReferenceManual
• The Unix Tree, tuhs.org – the source code of old versions of Unix

• Linux package management-related software
• Unix package management-related software
• Linux security software
• Unix security-related software

• Articles with short description
• Short description is different from Wikidata