420 lines
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420 lines
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<TITLE>Backup-With-MSDOS mini-HOWTO: The technique</TITLE>
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<H2><A NAME="s2">2. The technique</A></H2>
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<P>Throughout this description I will refer to two machines as ``<CODE>msdos</CODE>''
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and ``<CODE>linux</CODE>''. ``<CODE>msdos</CODE>'' is the name of the machine
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which has the tape drive and is usually running MS-DOS.
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``<CODE>linux</CODE>'' is the Linux machine whose disk
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you are trying to back up or restore to the tape drive.
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For simplicity I will refer to the first machine as ``<CODE>msdos</CODE>''
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even when it is booted into and running Linux.
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Further, all path names in this document should be considered
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to be relative to the Linux machine with the Search-And-Rescue (SAR)
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disks mounted somewhere on the system.
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That means that the file <CODE>/etc/passwd</CODE> is the password file for
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your Linux machine's hard drive, while, for instance,
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<CODE>/tape144/etc/passwd</CODE> is the corresponding file on the floppy disk.
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<P>
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<P>I am using Karel Kubat's backup scripts, version 1.03, available at
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<BLOCKQUOTE><CODE>
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<A HREF="ftp://sunsite.enc.edu:/pub/Linux/system/Backup/backup-1.03.tar.gz">ftp://sunsite.enc.edu:/pub/Linux/system/Backup/backup-1.03.tar.gz</A></CODE></BLOCKQUOTE>
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Throughout this document I will refer to these simply as
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``<CODE>the backup scripts</CODE>''.
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You do not have to use these scripts for your own backups to tape.
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I like these scripts as they use afio to form
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an uncompressed archive of compressed files,
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rather than a compressed archive of uncompressed files.
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The former is much safer if there is a media read error during the restore.
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I understand that Karel is no longer supporting backup,
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and now has produced 'tob', or tape oriented backup.
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While I haven't tried the new package myself,
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it cannot make a significant difference to the procedure outlined here.
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<P>First of all, obtain the ftape module. It is a part of all modern kernels,
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but if you are using an older kernel you can find the module at:
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<BLOCKQUOTE><CODE>
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<A HREF="ftp://sunsite.unc.edu/pub/Linux/kernel/tapes/ftape-2.05.tar.gz">ftp://sunsite.unc.edu/pub/Linux/kernel/tapes/ftape-2.05.tar.gz</A></CODE></BLOCKQUOTE>
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Next, get a Slackware boot disk
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(I got the net disk, but it doesn't make much difference) and
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the <CODE>tape144</CODE> root disk,
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and put the images onto 3"1/2 floppies.
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<P>The <CODE>ftape</CODE> module will only work
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if it is installed in the kernel which was running when you compiled it.
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I could not get it to work with the <CODE>ftape.o</CODE> module on
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the <CODE>tape144</CODE> root disk,
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I think because that module has been stripped of symbols and won't install.
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So, you now have to make a new kernel with network and ftape support,
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and if you're running an old kernel, a new <CODE>ftape.o</CODE>.
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Read the directions which ship with the <CODE>ftape</CODE> archive for
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directions at this stage.
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Remember that the kernel you compile must support the Ethernet cards
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on both the Linux machine and the MS-DOS machine.
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<P>Copy the newly created kernel image over top of the one on the Net boot disk.
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Use <CODE>/bin/cp</CODE>, do not create a boot disk with the ``<CODE>dd</CODE>''
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command as you would to create a bootable kernel image.
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Write protect the boot disk, and label it: SAR#1.
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<P>Now, mount the <CODE>tape144</CODE> root disk.
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I'll assume that the mount point is <CODE>/tape144</CODE>,
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to avoid confusion in file names.
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We need to free some space on it, so delete the following files:
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<BLOCKQUOTE><CODE>
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<PRE>
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/tape144/bin/dialog
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/tape144/bin/elvis
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/tape144/bin/vi
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/tape144/boot/ftape.o
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</PRE>
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</CODE></BLOCKQUOTE>
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<P>Now, create a new file:
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<BLOCKQUOTE><CODE>
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<PRE>
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/tape144/etc/exports
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</PRE>
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</CODE></BLOCKQUOTE>
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which contains the following line:
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<BLOCKQUOTE><CODE>
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<PRE>
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/mnt msdos(ro)
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</PRE>
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</CODE></BLOCKQUOTE>
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Where ``<CODE>msdos</CODE>'' should be replaced with the name or IP#
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of the MS-DOS machine which has the tape drive installed.
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<P>Next, so that you don't have to rely on a name server,
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add lines to the file <CODE>/tape144/etc/hosts</CODE> with
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the names and IP numbers of the Linux and MS-DOS machines.
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For instance, mine contains the following two lines:
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<BLOCKQUOTE><CODE>
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<PRE>
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128.100.75.114 caliban.physics.utoronto.ca caliban caliban.physics
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128.100.75.111 ariel.physics.utoronto.ca ariel ariel.physics
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</PRE>
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</CODE></BLOCKQUOTE>
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<P>Now, there's some sort of problem with the inetd configuration.
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We have to put the full path name of the rsh daemon in it.
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Change line 19 of <CODE>/tape144/etc/inetd.conf</CODE> to read:
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<BLOCKQUOTE><CODE>
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<PRE>
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shell stream tcp nowait root /usr/etc/tcpd /usr/etc/in.rshd
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</PRE>
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</CODE></BLOCKQUOTE>
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<P>Add local net routing information to <CODE>/tape144/etc/rc.d/rc.inet1</CODE>
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to enable the MS-DOS machine to use the network.
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The format of this depends on your network configuration,
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you can just copy the appropriate format out of your Linux
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<CODE>/etc/rc.d/rc.inet1</CODE>.
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For my network, the lines that have to be added are:
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<BLOCKQUOTE><CODE>
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<PRE>
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/etc/ifconfig eth0 128.100.75.111 broadcast 128.100.75.0 netmask 255.255.255.0
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/etc/route add -net 128.100.75.0 netmask 255.255.255.0
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</PRE>
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</CODE></BLOCKQUOTE>
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The IP# in the ifconfig entry is that of the MS-DOS machine.
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<P>Now, copy this file into <CODE>/tape144/etc/rc.d/rc.inet1-l</CODE>,
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and change the IP# in the new file to reflect that of
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the Linux machine rather than the MS-DOS machine.
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<P>Next, clip out lines 3 to 11 of <CODE>/tape144/etc/rc.local</CODE>.
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That's an if statement which executes the <CODE>rc.inet*</CODE> files.
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We don't want this to happen during the bootup.
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<P>Create a new file: <CODE>/tape144/root/.rhosts</CODE> containing the line:
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<BLOCKQUOTE><CODE>
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<PRE>
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linux root
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</PRE>
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</CODE></BLOCKQUOTE>
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where, again, ``<CODE>linux</CODE>'' is replaced with the full machine name
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(including domain) or the IP# of the Linux machine.
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<P>Fill in the password field in <CODE>/tape144/etc/passwd</CODE>
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for the root login to keep people from logging onto the MS-DOS machine
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while you're doing the backup.
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You can do this by copying the corresponding field from your Linux machine's
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<CODE>/etc/passwd file</CODE>.
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<P>Copy /usr/bin/rsh into /tape144/usr/bin.
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<P>Copy the following files from <CODE>/usr/etc</CODE> into <CODE>/tape144/usr/etc</CODE>:
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<BLOCKQUOTE><CODE>
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<PRE>
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in.rshd
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rpc.mountd
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rpc.nfsd
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rpc.portmap
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services
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tcpd
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</PRE>
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</CODE></BLOCKQUOTE>
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<P>Create a new script, <CODE>/tape144/bin/tapesetup</CODE>,
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which consists of the following:
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(change ``<CODE>linux</CODE>'' to reflect your Linux machine name).
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<BLOCKQUOTE><CODE>
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<PRE>
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#! /bin/sh
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/bin/sh /etc/rc.d/rc.inet1
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/bin/sh /etc/rc.d/rc.inet2
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/bin/mount linux:/nfs /mnt
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/bin/insmod /mnt/ftape.o
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</PRE>
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</CODE></BLOCKQUOTE>
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Note that newer kernels will not require the insmod line.
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<P>Next, create another new script, <CODE>/tape144/bin/msdosset</CODE>, as follows:
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(change ``<CODE>linux</CODE>'' to reflect your Linux machine name).
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<BLOCKQUOTE><CODE>
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<PRE>
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#! /bin/sh
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/bin/sh /etc/rc.d/rc.inet1
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/bin/sh /etc/rc.d/rc.inet2
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mount linux:/mnt /mnt
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/bin/insmod /mnt/ftape.o
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</PRE>
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</CODE></BLOCKQUOTE>
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As above, newer kernels will not require the insmod line.
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<P>Create a readable file, <CODE>/tape144/root/notes</CODE>,
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which contains this helpful information for use in full recovery:
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<BLOCKQUOTE><CODE>
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<PRE>
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For a full recovery to a trashed hard disk,
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boot the Linux machine with the SAR disks #1 and #2
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then type the following:
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/bin/sh /etc/rc.d/rc.inet1-l
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/bin/sh /etc/rc.d/rc.inet2
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/usr/etc/rpc.portmap
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/usr/etc/rpc.mountd
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/usr/etc/rpc.nfsd
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Next, insert SAR disk #3 and type:
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mount /dev/fd0 /mnt
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Create a new mount point, with:
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mkdir /mnt2
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and mount your Linux hard disk partition on this point.
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You may have to reformat the partition first, if so,
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follow the directions in the Linux Installation HOWTO.
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The SAR disks contain all the files necessary to do the reformat.
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Finally, use disks SAR#1 and SAR#2 to boot up
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the MS-DOS machine and run the /bin/msdosset script on that machine.
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It will take about a minute to run that script because it is getting
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an NSF file from a floppy drive, so be patient.
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Now, recover the tape to /mnt2 on the Linux machine.
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</PRE>
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</CODE></BLOCKQUOTE>
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<P>If you are using the backup scripts you will need to
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copy 'afio' into the <CODE>/tape144/local/bin</CODE> subdirectory.
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It is not necessary to have the rest of the backup script files
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on the recovery disks, an archive can be recovered using only 'afio' and 'gzip'.
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<P>I was unable to use the backup scripts as they come shipped.
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The tape archive appears to build cleanly, but it is unrecoverable.
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I found that removing the block size and conversion statements fixed it.
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Here is the patch to the ``<CODE>netbackup</CODE>'' script.
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Apply this patch to the Linux machine's hard disk copy of 'netbackup'
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as well as to the copy on the SAR disks.
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<BLOCKQUOTE><CODE>
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<PRE>
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*** netbackup.orig Mon Jan 9 17:22:32 1995
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--- netbackup Mon Jan 9 17:23:25 1995
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***************
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*** 35,41 ****
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"'mknod", devname, "p'");
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exec ("su -", USERNAME, "-c",
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"'rsh ", REMOTE_HOST,
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! "\"dd", "of=" REMOTE_DEVICE, "obs=20k", "conv=sync\"",
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"<", devname,
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"'&"
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);
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--- 35,41 ----
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"'mknod", devname, "p'");
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exec ("su -", USERNAME, "-c",
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"'rsh ", REMOTE_HOST,
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! "\"dd", "of=" REMOTE_DEVICE, "\"",
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"<", devname,
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"'&"
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);
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***************
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*** 50,56 ****
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"'mknod", devname, "p'");
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exec ("su", USERNAME, "-c",
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"'rsh ", REMOTE_HOST,
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! "\"dd", "if=" REMOTE_DEVICE, "ibs=20k", "conv=sync\"",
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">", devname,
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"'&"
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);
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--- 50,56 ----
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"'mknod", devname, "p'");
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exec ("su", USERNAME, "-c",
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"'rsh ", REMOTE_HOST,
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! "\"dd", "if=" REMOTE_DEVICE, "\"",
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">", devname,
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"'&"
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);
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</PRE>
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</CODE></BLOCKQUOTE>
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<P>You have now finished your SAR disk #2.
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Write protect it.
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<P>Next, mount a clean, formatted disk
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(create it with <CODE>fdformat</CODE> and <CODE>mkfs</CODE>).
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Copy the <CODE>ftape.o</CODE> file onto it, and label it SAR#3.
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For some reason things go badly if you write protect this disk,
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so leave it write-enabled.
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<P>On the Linux machine, create a new directory for NFS file serving.
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I made a directory:
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<BLOCKQUOTE><CODE>
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<PRE>
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/nfs
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</PRE>
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</CODE></BLOCKQUOTE>
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Put the <CODE>ftape.o</CODE> (unstripped, about 500+ kB) into this subdirectory.
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Create an entry in your Linux's exports file <CODE>/etc/exports</CODE>:
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<BLOCKQUOTE><CODE>
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<PRE>
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/nfs msdos(ro)
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</PRE>
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</CODE></BLOCKQUOTE>
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Note that all files in your NFS directory and it's subdirectories
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are not secure.
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Somebody else could boot the MS-DOS machine into Linux with
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his own boot disks and mount this directory,
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so be certain that you don't put anything sensitive in your NFS subdirectory.
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<P>Restart your NFS daemons, <CODE>rpc.mountd</CODE> and <CODE>rpc.nfsd</CODE>.
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They don't seem to take kindly to a <CODE>SIGHUP</CODE> restart,
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so kill them and reinvoke them.
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If you're not activating these daemons in your <CODE>/etc/rc.d/rc.inet2</CODE>
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you might want to do so now.
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<P>OK, now we're all set to back up and recover.
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To make a full backup from the Linux machine,
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boot the MS-DOS machine with SAR#1.
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When prompted for the second disk, load SAR#2. Log in as root,
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and execute the script: <CODE>/bin/tapesetup</CODE>.
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Log out of the MS-DOS machine.
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If you're using the backup scripts, the netbackup command will now work.
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You can also use the ``<CODE>-f msdos:/dev/ftape</CODE>'' switch on GNU
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<CODE>tar</CODE>, <CODE>cpio</CODE>, or <CODE>mt</CODE>, and make your backup this way.
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If you have a backup program,
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which is only capable of writing to a local file,
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do the following.
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Assume that the backup program is called ``<CODE>localbackup</CODE>'' and
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writes to the file represented by its command line argument:
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<BLOCKQUOTE><CODE>
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<PRE>
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mknod /tmp/tapepipe p
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rsh msdos dd of=/dev/ftape < /tmp/tapepipe &
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localbackup /tmp/tapepipe
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</PRE>
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</CODE></BLOCKQUOTE>
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when it's done, delete <CODE>/tmp/tapepipe</CODE>.
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<P>Recovering to a live Linux machine:
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the <CODE>netbackup</CODE> script, <CODE>tar</CODE>, <CODE>cpio</CODE>,
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and so on will all work without special actions on the part of the operator.
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If you have a local recovery program which recovers from a file, do this:
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<BLOCKQUOTE><CODE>
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<PRE>
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mknod /tmp/tapepipe p
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rsh -n msdos dd if=/dev/ftape >> /tmp/tapepipe &
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localrecovery /tmp/tapepipe
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</PRE>
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</CODE></BLOCKQUOTE>
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and delete <CODE>/tmp/tapepipe</CODE> when you're done.
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<P>Notice that I'm using '<CODE>rsh</CODE>' to the root user on the MS-DOS machine.
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This works with a correct <CODE>.rhosts</CODE> entry.
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The configuration on the '<CODE>tape144</CODE>' disk allows <CODE>rsh</CODE> to root,
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but does not allow <CODE>telnet</CODE> or <CODE>rlogin</CODE> to root,
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logins are restricted to the console.
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This is good for security.
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<P>If you are worried about a root <CODE>.rhost</CODE> file,
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you can create a new user on SAR#2, ``<CODE>tapeuser</CODE>'',
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with permissions to operate the tape drive but not the disks
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(create a new group and put tapeuser in that group,
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then <CODE>chown</CODE> and <CODE>chmod</CODE> the files <CODE>/dev/rft*</CODE> and
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<CODE>/dev/nrft*</CODE>).
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Your backup program then has to know to <CODE>rsh</CODE> to that username
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rather than to root.
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Of course, now there must be an <CODE>.rhosts</CODE> file in
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<CODE>~tapeuser</CODE> on SAR#2.
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For my own use, I have chosen this course, rather than a root <CODE>.rhosts</CODE>.
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<P>Finally, the directions for a complete recovery to a trashed hard disk.
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This assumes that the Linux partition is completely unrecoverable.
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If necessary, reformat that partition as described in the Linux
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Installation HOWTO. Boot the Linux machine from SAR disk #1.
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When prompted, insert disk #2.
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Now, follow the directions in the file <CODE>/root/notes</CODE>
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(this was <CODE>/tape144/root/notes</CODE> when it was mounted on
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your Linux machine).
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Once both machines have been booted up, run the recovery routine you need.
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If you are running the backup scripts you can do it as follows:
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<OL>
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<LI>change directory to the mount point of the hard disk partition
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which you will be recovering.</LI>
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<LI>if any mounted volumes are on the backup,
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and you want to recover them,
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create the mount points within the hard disk partition and
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mount the volumes.</LI>
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<LI>Enter the command:
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<BLOCKQUOTE><CODE>
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<PRE>
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rsh -n msdos dd if=/dev/ftape | afio -i -v -Z -c 1024 -
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</PRE>
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</CODE></BLOCKQUOTE>
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or
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<BLOCKQUOTE><CODE>
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<PRE>
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rsh -n -l tapeuser msdos dd if=/dev/ftape | afio -i -v -Z -c 1024 -
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</PRE>
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</CODE></BLOCKQUOTE>
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or
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<BLOCKQUOTE><CODE>
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<PRE>
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mknod /tmp/backpipe p
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rsh -n msdos dd if=/dev/ftape >> /tmp/backpipe &
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afio -i -v -Z -c 1024 /tmp/backpipe
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</PRE>
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</CODE></BLOCKQUOTE>
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</LI>
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</OL>
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This reads the tape on the remote machine, writing the result to stdout,
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where <CODE>afio</CODE> picks it up.
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The '<CODE>-i</CODE>' switch tells it to recover the files relative to
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the current working directory (which is the root of the hard disk partition). '<CODE>-v</CODE>' is verbose, listing the files as they are recovered. '<CODE>-Z</CODE>' tells afio that this is an archive of individually compressed files. '<CODE>-c 1024</CODE>' tells it to use a 5 MB streaming buffer
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to avoid a lot of tape rewinding.
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<HR>
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<A HREF="Backup-With-MSDOS-3.html">Next</A>
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<A HREF="Backup-With-MSDOS-1.html">Previous</A>
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