Backup-With-MSDOS.pdf

Backup−With−MSDOS mini−HOWTO

Table of Contents

Backup−With−MSDOS mini−HOWTO. ..........................................................................................................1

Christopher Neufeld, neufeld@physics.utoronto.ca. ...............................................................................1

1. Preface/Introduction. ............................................................................................................................1

2. The technique. ......................................................................................................................................1

3. Notes. ...................................................................................................................................................1

4. Copyright. ............................................................................................................................................1

1. Preface/Introduction. ............................................................................................................................1

2. The technique. ......................................................................................................................................1

3. Notes. ...................................................................................................................................................7

4. Copyright. ............................................................................................................................................8

Backup−With−MSDOS mini−HOWTO

Christopher Neufeld, neufeld@physics.utoronto.ca

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 machine.

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 ( jlnance@isscad.com ) 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

Backup−With−MSDOS mini−HOWTO

Backup−With−MSDOS mini−HOWTO

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

ftp://sunsite.enc.edu:/pub/Linux/system/Backup/backup−1.03.tar.gz

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 uncompressed

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 at:

ftp://sunsite.unc.edu/pub/Linux/kernel/tapes/ftape−2.05.tar.gz

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:

/tape144/bin/dialog

/tape144/bin/elvis

/tape144/bin/vi

/tape144/boot/ftape.o

Now, create a new file:

/tape144/etc/exports

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.

Backup−With−MSDOS mini−HOWTO

Backup−With−MSDOS mini−HOWTO

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:

128.100.75.114 caliban.physics.utoronto.ca caliban caliban.physics

128.100.75.111 ariel.physics.utoronto.ca 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 128.100.75.111 broadcast 128.100.75.0 netmask 255.255.255.0

/etc/route add −net 128.100.75.0 netmask 255.255.255.0

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 :

in.rshd

rpc.mountd

rpc.nfsd

rpc.portmap

services

tcpd

Create a new script, /tape144/bin/tapesetup , which consists of the following: (change `` linux '' to

reflect your Linux machine name).

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