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  Backup-With-MSDOS mini-HOWTO
  Christopher Neufeld,
  v, 5 August 1997

  This HOWTO describes how to use a Linux-compatible tape drive
  installed on an MS-DOS machine to back up the filesystem of a Linux

  Table of Contents

  1. Preface/Introduction

  2. The technique

  3. Notes

  4. Copyright


  1.  Preface/Introduction

  Earlier I posed the question on the Net, how does one back up a Linux
  machine to a Colorado Jumbo 250 tape drive on an MS-DOS machine.  From
  the email I received, it seems that this is a frequently pondered
  problem.  Now that I've figured it out, I'm posting the method.  If
  anybody wants to massage this into a HOWTO document, let me know.  I
  should thank Jim Nance ( for pointing out that an
  MS-DOS machine need not always be an MS-DOS machine.  This technique
  should also work for any other tape drive supported by the ftape
  module, and for SCSI tape drives with suitable obvious changes (i.e.
  substituting /dev/st0 for /dev/ftape).

  The criteria I set were that the resulting setup should be as secure
  as possible and should be fairly simple, and take up little or no
  space on the MS-DOS machine's hard drive. It should also be capable of
  recovering from the worst system corruptions, up to and including the
  theft of the hard disk, requiring a restore to a bare Linux file
  system.  The technique described here uses no hard drive space on the
  MS-DOS machine, though it requires that that machine be assigned an
  IP#.  You will need three formatted, blank 1.44MB diskettes.

  2.  The technique

  Throughout this description I will refer to two machines as ``msdos''
  and ``linux''. ``msdos'' is the name of the machine which has the tape
  drive and is usually running MS-DOS.  ``linux'' is the Linux machine
  whose disk you are trying to back up or restore to the tape drive.
  For simplicity I will refer to the first machine as ``msdos'' even
  when it is booted into and running Linux.  Further, all path names in
  this document should be considered to be relative to the Linux machine
  with the Search-And-Rescue (SAR) disks mounted somewhere on the
  system.  That means that the file /etc/passwd is the password file for
  your Linux machine's hard drive, while, for instance,
  /tape144/etc/passwd is the corresponding file on the floppy disk.

  I am using Karel Kubat's backup scripts, version 1.03, available at


  Throughout this document I will refer to these simply as ``the backup
  scripts''.  You do not have to use these scripts for your own backups
  to tape.  I like these scripts as they use afio to form an uncom�
  pressed archive of compressed files, rather than a compressed archive
  of uncompressed files.  The former is much safer if there is a media
  read error during the restore.  I understand that Karel is no longer
  supporting backup, and now has produced 'tob', or tape oriented
  backup.  While I haven't tried the new package myself, it cannot make
  a significant difference to the procedure outlined here.

  First of all, obtain the ftape module. It is a part of all modern
  kernels, but if you are using an older kernel you can find the module


  Next, get a Slackware boot disk (I got the net disk, but it doesn't
  make much difference) and the tape144 root disk, and put the images
  onto 3"1/2 floppies.

  The ftape module will only work if it is installed in the kernel which
  was running when you compiled it.  I could not get it to work with the
  ftape.o module on the tape144 root disk, I think because that module
  has been stripped of symbols and won't install.  So, you now have to
  make a new kernel with network and ftape support, and if you're
  running an old kernel, a new ftape.o.  Read the directions which ship
  with the ftape archive for directions at this stage.  Remember that
  the kernel you compile must support the Ethernet cards on both the
  Linux machine and the MS-DOS machine.

  Copy the newly created kernel image over top of the one on the Net
  boot disk.  Use /bin/cp, do not create a boot disk with the ``dd''
  command as you would to create a bootable kernel image.  Write protect
  the boot disk, and label it: SAR#1.

  Now, mount the tape144 root disk.  I'll assume that the mount point is
  /tape144, to avoid confusion in file names.  We need to free some
  space on it, so delete the following files:


  Now, create a new file:


  which contains the following line:

       /mnt    msdos(ro)

  Where ``msdos'' should be replaced with the name or IP# of the MS-DOS
  machine which has the tape drive installed.

  Next, so that you don't have to rely on a name server, add lines to
  the file /tape144/etc/hosts with the names and IP numbers of the Linux
  and MS-DOS machines.  For instance, mine contains the following two
  lines: caliban caliban.physics ariel ariel.physics

  Now, there's some sort of problem with the inetd configuration.  We
  have to put the full path name of the rsh daemon in it.  Change line
  19 of /tape144/etc/inetd.conf to read:

       shell   stream  tcp     nowait  root    /usr/etc/tcpd   /usr/etc/in.rshd

  Add local net routing information to /tape144/etc/rc.d/rc.inet1 to
  enable the MS-DOS machine to use the network.  The format of this
  depends on your network configuration, you can just copy the
  appropriate format out of your Linux /etc/rc.d/rc.inet1.  For my
  network, the lines that have to be added are:

       /etc/ifconfig eth0 broadcast netmask
       /etc/route add -net netmask

  The IP# in the ifconfig entry is that of the MS-DOS machine.

  Now, copy this file into /tape144/etc/rc.d/rc.inet1-l, and change the
  IP# in the new file to reflect that of the Linux machine rather than
  the MS-DOS machine.

  Next, clip out lines 3 to 11 of /tape144/etc/rc.local.  That's an if
  statement which executes the rc.inet* files.  We don't want this to
  happen during the bootup.

  Create a new file: /tape144/root/.rhosts containing the line:

       linux root

  where, again, ``linux'' is replaced with the full machine name
  (including domain) or the IP# of the Linux machine.

  Fill in the password field in /tape144/etc/passwd for the root login
  to keep people from logging onto the MS-DOS machine while you're doing
  the backup.  You can do this by copying the corresponding field from
  your Linux machine's /etc/passwd file.

  Copy /usr/bin/rsh into /tape144/usr/bin.

  Copy the following files from /usr/etc into /tape144/usr/etc:


  Create a new script, /tape144/bin/tapesetup, which consists of the
  following: (change ``linux'' to reflect your Linux machine name).

       #! /bin/sh

       /bin/sh /etc/rc.d/rc.inet1
       /bin/sh /etc/rc.d/rc.inet2

       /bin/mount linux:/nfs /mnt
       /bin/insmod /mnt/ftape.o

  Note that newer kernels will not require the insmod line.

  Next, create another new script, /tape144/bin/msdosset, as follows:
  (change ``linux'' to reflect your Linux machine name).

       #! /bin/sh

       /bin/sh /etc/rc.d/rc.inet1
       /bin/sh /etc/rc.d/rc.inet2

       mount linux:/mnt /mnt
       /bin/insmod /mnt/ftape.o

  As above, newer kernels will not require the insmod line.

  Create a readable file, /tape144/root/notes, which contains this
  helpful information for use in full recovery:

  For a full recovery to a trashed hard disk,
  boot the Linux machine with the SAR disks #1 and #2
  then type the following:

     /bin/sh /etc/rc.d/rc.inet1-l
     /bin/sh /etc/rc.d/rc.inet2


  Next, insert SAR disk #3 and type:

     mount /dev/fd0 /mnt

  Create a new mount point, with:

     mkdir /mnt2

  and mount your Linux hard disk partition on this point.
  You may have to reformat the partition first, if so,
  follow the directions in the Linux Installation HOWTO.
  The SAR disks contain all the files necessary to do the reformat.

  Finally, use disks SAR#1 and SAR#2 to boot up
  the MS-DOS machine and run the /bin/msdosset script on that machine.
  It will take about a minute to run that script because it is getting
  an NSF file from a floppy drive, so be patient.
  Now, recover the tape to /mnt2 on the Linux machine.

  If you are using the backup scripts you will need to copy 'afio' into
  the /tape144/local/bin subdirectory.  It is not necessary to have the
  rest of the backup script files on the recovery disks, an archive can
  be recovered using only 'afio' and 'gzip'.

  I was unable to use the backup scripts as they come shipped.  The tape
  archive appears to build cleanly, but it is unrecoverable.  I found
  that removing the block size and conversion statements fixed it.  Here
  is the patch to the ``netbackup'' script.  Apply this patch to the
  Linux machine's hard disk copy of 'netbackup' as well as to the copy
  on the SAR disks.

  *** netbackup.orig      Mon Jan  9 17:22:32 1995
  --- netbackup   Mon Jan  9 17:23:25 1995
  *** 35,41 ****
                    "'mknod", devname, "p'");
        exec ("su -", USERNAME, "-c",
                    "'rsh ", REMOTE_HOST,
  !                       "\"dd", "of=" REMOTE_DEVICE, "obs=20k", "conv=sync\"",
                          "<", devname,
  --- 35,41 ----
                    "'mknod", devname, "p'");
        exec ("su -", USERNAME, "-c",
                    "'rsh ", REMOTE_HOST,
  !                       "\"dd", "of=" REMOTE_DEVICE, "\"",
                          "<", devname,
  *** 50,56 ****
                    "'mknod", devname, "p'");
        exec ("su", USERNAME, "-c",
                    "'rsh ", REMOTE_HOST,
  !                       "\"dd", "if=" REMOTE_DEVICE, "ibs=20k", "conv=sync\"",
                          ">", devname,
  --- 50,56 ----
                    "'mknod", devname, "p'");
        exec ("su", USERNAME, "-c",
                    "'rsh ", REMOTE_HOST,
  !                       "\"dd", "if=" REMOTE_DEVICE, "\"",
                          ">", devname,

  You have now finished your SAR disk #2.  Write protect it.

  Next, mount a clean, formatted disk (create it with fdformat and
  mkfs).  Copy the ftape.o file onto it, and label it SAR#3.  For some
  reason things go badly if you write protect this disk, so leave it

  On the Linux machine, create a new directory for NFS file serving.  I
  made a directory:


  Put the ftape.o (unstripped, about 500+ kB) into this subdirectory.
  Create an entry in your Linux's exports file /etc/exports:

       /nfs    msdos(ro)

  Note that all files in your NFS directory and it's subdirectories are
  not secure.  Somebody else could boot the MS-DOS machine into Linux
  with his own boot disks and mount this directory, so be certain that
  you don't put anything sensitive in your NFS subdirectory.

  Restart your NFS daemons, rpc.mountd and rpc.nfsd.  They don't seem to
  take kindly to a SIGHUP restart, so kill them and reinvoke them.  If
  you're not activating these daemons in your /etc/rc.d/rc.inet2 you
  might want to do so now.

  OK, now we're all set to back up and recover.  To make a full backup
  from the Linux machine, boot the MS-DOS machine with SAR#1.  When
  prompted for the second disk, load SAR#2. Log in as root, and execute
  the script: /bin/tapesetup.  Log out of the MS-DOS machine.  If you're
  using the backup scripts, the netbackup command will now work.  You
  can also use the ``-f msdos:/dev/ftape'' switch on GNU tar, cpio, or
  mt, and make your backup this way.  If you have a backup program,
  which is only capable of writing to a local file, do the following.
  Assume that the backup program is called ``localbackup'' and writes to
  the file represented by its command line argument:

       mknod /tmp/tapepipe p
       rsh msdos dd of=/dev/ftape < /tmp/tapepipe &
       localbackup /tmp/tapepipe

  when it's done, delete /tmp/tapepipe.

  Recovering to a live Linux machine: the netbackup script, tar, cpio,
  and so on will all work without special actions on the part of the
  operator.  If you have a local recovery program which recovers from a
  file, do this:

       mknod /tmp/tapepipe p
       rsh -n msdos dd if=/dev/ftape >> /tmp/tapepipe &
       localrecovery /tmp/tapepipe

  and delete /tmp/tapepipe when you're done.

  Notice that I'm using 'rsh' to the root user on the MS-DOS machine.
  This works with a correct .rhosts entry.  The configuration on the
  'tape144' disk allows rsh to root, but does not allow telnet or rlogin
  to root, logins are restricted to the console.  This is good for

  If you are worried about a root .rhost file, you can create a new user
  on SAR#2, ``tapeuser'', with permissions to operate the tape drive but
  not the disks (create a new group and put tapeuser in that group, then
  chown and chmod the files /dev/rft* and /dev/nrft*).  Your backup
  program then has to know to rsh to that username rather than to root.
  Of course, now there must be an .rhosts file in ~tapeuser on SAR#2.
  For my own use, I have chosen this course, rather than a root .rhosts.

  Finally, the directions for a complete recovery to a trashed hard
  disk.  This assumes that the Linux partition is completely
  unrecoverable.  If necessary, reformat that partition as described in
  the Linux Installation HOWTO. Boot the Linux machine from SAR disk #1.
  When prompted, insert disk #2.  Now, follow the directions in the file
  /root/notes (this was /tape144/root/notes when it was mounted on your
  Linux machine).  Once both machines have been booted up, run the
  recovery routine you need.  If you are running the backup scripts you
  can do it as follows:

  1. change directory to the mount point of the hard disk partition
     which you will be recovering.

  2. if any mounted volumes are on the backup, and you want to recover
     them, create the mount points within the hard disk partition and
     mount the volumes.

  3. Enter the command:

       rsh -n msdos dd if=/dev/ftape | afio -i -v -Z -c 1024 -


       rsh -n -l tapeuser msdos dd if=/dev/ftape | afio -i -v -Z -c 1024 -


       mknod /tmp/backpipe p
       rsh -n msdos dd if=/dev/ftape >> /tmp/backpipe &
       afio -i -v -Z -c 1024 /tmp/backpipe

  This reads the tape on the remote machine, writing the result to std�
  out, where afio picks it up.  The '-i' switch tells it to recover the
  files relative to the current working directory (which is the root of
  the hard disk partition).  '-v' is verbose, listing the files as they
  are recovered.  '-Z' tells afio that this is an archive of individu�
  ally compressed files.  '-c 1024' tells it to use a 5 MB streaming
  buffer to avoid a lot of tape rewinding.

  3.  Notes

  The commands listed in the /tape144/root/notes file could be run from
  a script.  When I tried, I got rpc setup errors.  I suspect it was
  just that the commands were run too quickly, and the portmapper hadn't
  properly installed itself.  I found that typing the sequence in
  manually worked fine, so I've recommended that.

  I think this setup is secure.  Note that somebody can still get access
  to all your files if they go to the tape drive and pull the tape out
  before you get there, then then read the tape themselves.  People with
  very sensitive data might consider encrypting the stream from the
  archiver.  Archive to standard output and pipe the output to the
  encrypter, and redirect the output of the encrypter to append to the
  named pipe /tmp/tapepipe as described above. Note that errors in the
  recovery process will result in all files after that point being
  unrecoverable, as the entire archive is now a single DES-encrypted
  stream.  It is possible to use options on afio to send each file in
  the archive first through gzip, then into an encryption program like
  des, but note that this compressing first does provide a fair amount
  of known plaintext for determined code breakers to work with, so a
  better approach might be to skip the gzip step and simply encrypt it
  with des, at the expense of significantly more tape area. Needless to
  say, DES encrypted files don't compress.

  The rc.inet1 directions I've included will allow only communication
  with the local network, not the rest of the world through a gateway.

  During a full recovery to a blank hard disk the SAR disk #3 provides
  ftape.o to the MS-DOS machine through NFS.  This is because some old
  versions of the ftape module can't control some tape drives when there
  is a disk mounted in the floppy drive. With newer kernels, the entire
  NFS stuff can be omitted.

  This is very important.  ***TEST*** the SAR recovery procedure.  I
  did, but don't leave anything to chance.  Make sure that you can
  recover at least one file from your tape to the Linux machine using
  only the SAR disks (i.e. without mounting the hard disk).  If you
  can't reboot the Linux machine without inconveniencing a lot of users,
  change the setup information on the SAR disks to assign the ``linux''
  identity to another MS-DOS machine and then boot the two MS-DOS
  machines into Linux to make sure everything works.  Then, change the
  ``linux'' identity back again so that you have usable SAR disks.

  4.  Copyright

  Copyright Jan 10, 1995 by Christopher Neufeld

  Modified Feb 6, 1996.

  Modified Aug 5, 1997.

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