+.TH SUM 1L \" -*- nroff -*-
+.SH NAME
+sum \- checksum and count the blocks in a file
+.SH SYNOPSIS
+.B sum
+[\-rs] [\-\-sysv] [file...]
+.SH DESCRIPTION
+This manual page
+documents the GNU version of
+.BR sum .
+.B sum
+computes a 16-bit checksum for each named file, or the standard input
+if none are given or when a file named `\-' is given. It prints the
+checksum for each file along with the number of blocks in the file
+(rounded up), and the file name unless no arguments were given. By
+default, the GNU
+.B sum
+computes checksums using an algorithm that is compatible with the BSD
+.B sum
+and prints file sizes in units of 1K blocks.
+.SS OPTIONS
+.TP
+.I \-r
+Use the default (BSD compatible) algorithm. This option is included
+for compatibility with the System V
+.BR sum .
+Unless the
+.I \-s
+option was also given, it has no effect.
+.TP
+.I "\-s, \-\-sysv"
+Compute checksums using an algorithm that is compatible with the one
+the System V
+.B sum
+uses by default
+and print file sizes in units of 512-byte blocks instead of 1K.
+.PP
+The long-named options can be introduced with `+' as well as `\-\-',
+for compatibility with previous releases. Eventually support for `+'
+will be removed, because it is incompatible with the POSIX.2 standard.