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+.\" Copyright (c) 1993
+.\"	The Regents of the University of California.  All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\" 3. Neither the name of the University nor the names of its contributors
+.\"    may be used to endorse or promote products derived from this software
+.\"    without specific prior written permission.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.Dd June 11, 2017
+.Dt GETBSIZE 3
+.Os
+.Sh NAME
+.Nm getbsize
+.Nd get preferred block size
+.Sh LIBRARY
+.Lb libc
+.Sh SYNOPSIS
+.In stdlib.h
+.Ft char *
+.Fn getbsize "int *headerlenp" "long *blocksizep"
+.Sh DESCRIPTION
+The
+.Fn getbsize
+function returns a preferred block size for reporting by system utilities
+.Xr df 1 ,
+.Xr du 1
+and
+.Xr ls 1 ,
+based on the value of the
+.Ev BLOCKSIZE
+environment variable.
+.Ev BLOCKSIZE
+may be specified directly in bytes, or in multiples of a kilobyte by
+specifying a number followed by ``K'' or ``k'', in multiples of a
+megabyte by specifying a number followed by ``M'' or ``m'' or in
+multiples of a gigabyte by specifying a number followed by ``G'' or
+``g''.
+Multiples must be integers.
+.Pp
+Valid values of
+.Ev BLOCKSIZE
+are 512 bytes to 1 gigabyte.
+Sizes less than 512 bytes are rounded up to 512 bytes, and sizes
+greater than 1 GB are rounded down to 1 GB.
+In each case
+.Fn getbsize
+produces a warning message via
+.Xr warnx 3 .
+.Pp
+The
+.Fn getbsize
+function returns a pointer to a null-terminated string describing
+the block size, something like
+.Dq 1K-blocks .
+The memory referenced by
+.Fa headerlenp
+is filled in with the length of the string (not including the
+terminating null).
+The memory referenced by
+.Fa blocksizep
+is filled in with block size, in bytes.
+.Sh SEE ALSO
+.Xr df 1 ,
+.Xr du 1 ,
+.Xr ls 1 ,
+.Xr systat 1 ,
+.Xr environ 7
+.Sh HISTORY
+The
+.Fn getbsize
+function first appeared in
+.Bx 4.4 .