\"
\" This file is part of vbig.
\" Copyright (C) 2011 Richard Kettlewell
\" Copyright (C) 2013 Ian Jackson
\"
\" This program is free software: you can redistribute it and/or modify
\" it under the terms of the GNU General Public License as published by
\" the Free Software Foundation, either version 3 of the License, or
\" (at your option) any later version.
\"
\" This program is distributed in the hope that it will be useful,
\" but WITHOUT ANY WARRANTY; without even the implied warranty of
\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
\" GNU General Public License for more details.
\"
\" You should have received a copy of the GNU General Public License
\" along with this program.  If not, see <http://www.gnu.org/licenses/>.
\"
.TH vbig 1
.SH NAME
vbig \- create or verify a large but pseudo-random file
.SH SYNOPSIS
\fBvbig \fR[\fB--seed \fRSEED\fR] [\fB--both\fR|\fB--create\fR|\fB--verify\fR] \fIPATH \fR[\fISIZE\fR]
.br
\fBvbig \-\-help
.br
\fBvbig \-\-version
.SH DESCRIPTION
\fBvbig\fR creates a file of specified size full of predictable
psuedo-random data, and/or verifies that it has the expected contents.
The intended use is to test whether storage media really do what they
say on the tin.
.PP
By default vbig will generate a new random seed, write data to the
specified file or device until the device is full, read the data back
to check that everything written was properly stored, and report
the device's size.  Ideally, if you have privilege to do so, you
would also specify \fB-f\fR (to flush the operating system disk
cache between the write and read).  Also you probably want \fB-p\fR.
.PP
\fBPATH\fR can refer to an ordinary file on a mounted file system,
which vbig will create or truncate as necessary, or a block device.
Note that if its a file vbig won't delete it after it's done.  Also,
be careful when specifying a block device - don't accidentally
overwrite a filesystem you care about!  vbig doesn't do sanity checks
and is as dangerous as \fBdd\fR.
.PP
\fISIZE\fR may end with \fBK\fR, \fBM\fR or \fBG\fR to select (binary)
kilobytes, megabytes or gigabytes.
The size is mandatory when creating a file but optional when verifying
it, unless \-\-entire is specified.  If \fBSIZE\fR not specified when
writing-then-verifying, it is as if \fB\-\-entire\fR was specified.
.PP
If no seed or seed file is specified:
in \fB--both\fR mode a fresh random seed is read from the system's
random number generator; in other modes a fixed default seed is used.
.SH OPTIONS
.TP
.B --seed\fR, \fB-s \fISEED
Specifies the random seed to use.
Optional.
.TP
.B --seed-file\fR, \fB-S \fISEED-FILE
Specifies wehre the random seed should be read from.  The
first \fISEED-LENGTH\fR bytes will be used, or the whole file
if it is shorter.
.TP
.B --seed-length\fR, \fB-L \fISEED-LENGTH
Specifies the (maximum) seed length in bytes.
Optional; default is 2048.
.TP
.B --both\fR, \fB-b
Selects both mode.
\fIPATH\fR will be filled with \fISIZE\fR psuedo-random bytes and
then read to check that it contains the data just written.
This is the default.
.TP
.B --create\fR, \fB-c
Selects create mode.
\fIPATH\fR will be filled with \fISIZE\fR psuedo-random bytes.
.TP
.B --verify\fR, \fB-v
Selects verify mode.
Checks that \fIPATH\fR has exactly the contents that would be produced
by the equivalent \fB--create\fR call.
.TP
.B --flush\fR, \fB-f
Flush cached data after creating the file or before verifying it.
On some platforms, only root can use this option.
.TP
.B --progress\fR, \fB-p
Show the progress (in bytes) on stdout.
.TP
.B --entire\fR, \fB-e
When writing, keep going until the device is full (No space left
on device).  When reading, keep going until the end of the file
or device.  \fISIZE\fR should not be specified.  The actual size
written or verified will be printed to stdout.
.TP
.B --help\fR, \fB-h
Displays a usage message.
.TP
.B --version\fR, \fB-V
Displays the version strings.
.SH AUTHOR
Richard Kettlewell <rjk@greenend.org.uk>