From - Tue Nov 12 16:41:31 1996
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From: fish@daacdev1.stx.com ("John R. Vanderpool")
Newsgroups: comp.sys.sgi.admin
Subject: Re: trying to read a tape ... about to give up...
Date: 7 Nov 1996 16:54:10 GMT
Organization: NASA Goddard Space Flight Center -- Greenbelt, Maryland USA
Lines: 102
Message-ID: <55t47i$504@post.gsfc.nasa.gov>
References: <55o31s$gjk@r02n01.cac.psu.edu>
NNTP-Posting-Host: daacdev1.stx.com
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bauer@eetsg08.bd.psu.edu (Kenneth J. Bauer) writes:

>We do work for local companies, and they will bring a tape of their
>files in for us to load onto our SGI machines. Then we will look at 
>their files and do whatever to them. Well, usually an engineer will
>bring the tapes to us, and usually, they don't know how they were put
>onto the tape (tar, bru, .... option from their S/W program, etc.). 
>They hand the tape to me, and say here, get this up for us.

>Well, that is the case here. I can't seem to read this tape. It came from
>a Sun machine (I think), and I have tried everything I can think of.

>e.g.	tar -tvb 20; tar -tvb 16; tar -tvb 8 ; tar -tvf /dev/nrtape ....
>	bru -tvb 20; bru -tvf /dev/nrtape .....
>        dd if=/dev/rmt/tps0d7nrnsv bs=16b conv=swab | tar vtf -
>        dd if=/dev/rmt/tps0d7nrnsv bs=816b conv=swab | tar vtf -

maybe its not in tar or bru format - it might just be a straight file dump.
check out my mtutils package at ftp://daac.gsfc.nasa.gov/pub/system/mtutils.tar.Z

see if mtfile can guess the format (just uses standard file "magic"):
i probably should add a "swab" check to this script, but i rarely use it, only
wrote it cuz it seemed handy and was fun....

#!/bin/ksh
#
#       mtbs	- return blocksize of next block on magtape
#	mtfile	- run unix file "magic" on magtape
#
#  10-jul-1995 jrv initial release <john.vanderpool@gsfc.nasa.gov> (fish)
#
# note: no support for rmt w/ this utility (due to dd and mt blksize)
#

if [ "${1:-}" = "-i" ]; then shift; fi
tpdev="${1:-${TAPE:-/dev/nrtape}}"
self=`basename $0`

tmpdir="${TMPDIR:-/tmp}"
tmpfile=$tmpdir/mtutils.$$


if [ ! -c $tpdev -a ! -b $tpdev ]; then		# not a device file
  echo $tpdev is not a device file
  exit 1
fi


if [ `uname` = IRIX ]; then			# use irix blksize feature

  mt -t $tpdev blksize 1>/dev/null 2>&1		# reset irix/tps bug
  if [ $? -ne 0 ]; then
    echo "mt error encountered"
    mt -t $tpdev stat
    exit 1
  fi
  bs=`mt -t $tpdev blksize 2>&1 | grep Maximum | cut -f5 -d" "`	# get maxblksz

  let MAXDMASZ_BYTES="(1024-1)*4*1024"		# max default DMA on irix
  if [ bs -gt $MAXDMASZ_BYTES ]; then
    bs=$MAXDMASZ_BYTES
  fi

else
  bs=65533					# 64KB-3 is ok on most OS'es

fi


dd if=$tpdev of=$tmpfile count=1 bs=$bs >/dev/null 2>&1

if [ $? = 0 ]; then

  mt -t $tpdev bsr 1 >/dev/null 2>&1

  if [ $self = mtbs ]; then
    bytes=`ls -l $tmpfile | awk '{ print $5 }'`
    let mod=bytes%512
    if [ $mod -eq 0 ]; then
      let blocks=bytes/512
      echo bytes=$bytes blocks=$blocks
    else
      echo bytes=$bytes
    fi

  elif [ $self = mtfile ]; then
    file $tmpfile | sed "s%$tmpfile%$tpdev%"

  fi

  if [ -f $tmpfile ]; then /bin/rm $tmpfile; fi

else
 echo "dd error encountered"
 exit 1

fi
--
"it all looks fine to the naked eye,
  but it don't really happen that way at all..."      PT 

John R. <>< Vanderpool      <fish@daacdev1.stx.com>   NASA/GSFC/HSTX