backup-basics.html

FreeBSD操作系统的详细使用手册

<div class="SECT3">
<h3 class="SECT3"><a id="AEN25028" name="AEN25028">16.11.8.1 Before the Disaster</a></h3>

<p>There are only four steps that you need to perform in preparation for any disaster
that may occur.</p>

<p>First, print the disklabel from each of your disks (e.g. <tt class="COMMAND">disklabel
da0 | lpr</tt>), your file system table (<tt class="FILENAME">/etc/fstab</tt>) and all
boot messages, two copies of each.</p>

<p>Second, determine that the boot and fix-it floppies (<tt
class="FILENAME">boot.flp</tt> and <tt class="FILENAME">fixit.flp</tt>) have all your
devices. The easiest way to check is to reboot your machine with the boot floppy in the
floppy drive and check the boot messages. If all your devices are listed and functional,
skip on to step three.</p>

<p>Otherwise, you have to create two custom bootable floppies which have a kernel that
can mount all of your disks and access your tape drive. These floppies must contain: <tt
class="COMMAND">fdisk</tt>, <tt class="COMMAND">disklabel</tt>, <tt
class="COMMAND">newfs</tt>, <tt class="COMMAND">mount</tt>, and whichever backup program
you use. These programs must be statically linked. If you use <tt
class="COMMAND">dump</tt>, the floppy must contain <tt class="COMMAND">restore</tt>.</p>

<p>Third, create backup tapes regularly. Any changes that you make after your last backup
may be irretrievably lost. Write-protect the backup tapes.</p>

<p>Fourth, test the floppies (either <tt class="FILENAME">boot.flp</tt> and <tt
class="FILENAME">fixit.flp</tt> or the two custom bootable floppies you made in step
two.) and backup tapes. Make notes of the procedure. Store these notes with the bootable
floppy, the printouts and the backup tapes. You will be so distraught when restoring that
the notes may prevent you from destroying your backup tapes (How? In place of <tt
class="COMMAND">tar xvf /dev/sa0</tt>, you might accidentally type <tt
class="COMMAND">tar cvf /dev/sa0</tt> and over-write your backup tape).</p>

<p>For an added measure of security, make bootable floppies and two backup tapes each
time. Store one of each at a remote location. A remote location is NOT the basement of
the same office building. A number of firms in the World Trade Center learned this lesson
the hard way. A remote location should be physically separated from your computers and
disk drives by a significant distance.</p>

<div class="EXAMPLE"><a id="AEN25056" name="AEN25056"></a>
<p><b>Example 16-3. A Script for Creating a Bootable Floppy</b></p>

<pre class="PROGRAMLISTING">
#!/bin/sh
#
# create a restore floppy
#
# format the floppy
#
PATH=/bin:/sbin:/usr/sbin:/usr/bin

fdformat -q fd0
if [ $? -ne 0 ]
then
     echo "Bad floppy, please use a new one"
     exit 1
fi

# place boot blocks on the floppy
#
disklabel -w -B /dev/fd0c fd1440

#
# newfs the one and only partition
#
newfs -t 2 -u 18 -l 1 -c 40 -i 5120 -m 5 -o space /dev/fd0a

#
# mount the new floppy
#
mount /dev/fd0a /mnt

#
# create required directories
#
mkdir /mnt/dev
mkdir /mnt/bin
mkdir /mnt/sbin
mkdir /mnt/etc
mkdir /mnt/root
mkdir /mnt/mnt          # for the root partition
mkdir /mnt/tmp
mkdir /mnt/var

#
# populate the directories
#
if [ ! -x /sys/compile/MINI/kernel ]
then
     cat &#60;&#60; EOM
The MINI kernel does not exist, please create one.
Here is an example config file:
#
# MINI -- A kernel to get FreeBSD onto a disk.
#
machine         "i386"
cpu             "I486_CPU"
ident           MINI
maxusers        5

options         INET                    # needed for _tcp _icmpstat _ipstat
                                        #            _udpstat _tcpstat _udb
options         FFS                     #Berkeley Fast File System
options         FAT_CURSOR              #block cursor in syscons or pccons
options         SCSI_DELAY=15           #Be pessimistic about Joe SCSI device
options         NCONS=2                 #1 virtual consoles
options         USERCONFIG              #Allow user configuration with -c XXX

config          kernel  root on da0 swap on da0 and da1 dumps on da0

device          isa0
device          pci0

device          fdc0    at isa? port "IO_FD1" bio irq 6 drq 2 vector fdintr
device          fd0 at fdc0 drive 0

device          ncr0

device          scbus0

device          sc0 at isa? port "IO_KBD" tty irq 1 vector scintr
device          npx0    at isa? port "IO_NPX" irq 13 vector npxintr

device          da0
device          da1
device          da2

device          sa0

pseudo-device   loop            # required by INET
pseudo-device   gzip            # Exec gzipped a.out's
EOM
     exit 1
fi

cp -f /sys/compile/MINI/kernel /mnt

gzip -c -best /sbin/init &#62; /mnt/sbin/init
gzip -c -best /sbin/fsck &#62; /mnt/sbin/fsck
gzip -c -best /sbin/mount &#62; /mnt/sbin/mount
gzip -c -best /sbin/halt &#62; /mnt/sbin/halt
gzip -c -best /sbin/restore &#62; /mnt/sbin/restore

gzip -c -best /bin/sh &#62; /mnt/bin/sh
gzip -c -best /bin/sync &#62; /mnt/bin/sync

cp /root/.profile /mnt/root

cp -f /dev/MAKEDEV /mnt/dev
chmod 755 /mnt/dev/MAKEDEV

chmod 500 /mnt/sbin/init
chmod 555 /mnt/sbin/fsck /mnt/sbin/mount /mnt/sbin/halt
chmod 555 /mnt/bin/sh /mnt/bin/sync
chmod 6555 /mnt/sbin/restore

#
# create the devices nodes
#
cd /mnt/dev
./MAKEDEV std
./MAKEDEV da0
./MAKEDEV da1
./MAKEDEV da2
./MAKEDEV sa0
./MAKEDEV pty0
cd /

#
# create minimum file system table
#
cat &#62; /mnt/etc/fstab &#60;&#60;EOM
/dev/fd0a    /    ufs    rw  1  1
EOM

#
# create minimum passwd file
#
cat &#62; /mnt/etc/passwd &#60;&#60;EOM
root:*:0:0:Charlie &#38;:/root:/bin/sh
EOM

cat &#62; /mnt/etc/master.passwd &#60;&#60;EOM
root::0:0::0:0:Charlie &#38;:/root:/bin/sh
EOM

chmod 600 /mnt/etc/master.passwd
chmod 644 /mnt/etc/passwd
/usr/sbin/pwd_mkdb -d/mnt/etc /mnt/etc/master.passwd

#
# umount the floppy and inform the user
#
/sbin/umount /mnt
echo "The floppy has been unmounted and is now ready."
</pre>
</div>
</div>

<div class="SECT3">
<h3 class="SECT3"><a id="AEN25059" name="AEN25059">16.11.8.2 After the Disaster</a></h3>

<p>The key question is: did your hardware survive? You have been doing regular backups so
there is no need to worry about the software.</p>

<p>If the hardware has been damaged, the parts should be replaced before attempting to
use the computer.</p>

<p>If your hardware is okay, check your floppies. If you are using a custom boot floppy,
boot single-user (type <var class="LITERAL">-s</var> at the <samp
class="PROMPT">boot:</samp> prompt). Skip the following paragraph.</p>

<p>If you are using the <tt class="FILENAME">boot.flp</tt> and <tt
class="FILENAME">fixit.flp</tt> floppies, keep reading. Insert the <tt
class="FILENAME">boot.flp</tt> floppy in the first floppy drive and boot the computer.
The original install menu will be displayed on the screen. Select the <var
class="LITERAL">Fixit--Repair mode with CDROM or floppy.</var> option. Insert the <tt
class="FILENAME">fixit.flp</tt> when prompted. <tt class="COMMAND">restore</tt> and the
other programs that you need are located in <tt class="FILENAME">/mnt2/stand</tt>.</p>

<p>Recover each file system separately.</p>

<p>Try to <tt class="COMMAND">mount</tt> (e.g. <tt class="COMMAND">mount /dev/da0a
/mnt</tt>) the root partition of your first disk. If the disklabel was damaged, use <tt
class="COMMAND">disklabel</tt> to re-partition and label the disk to match the label that
you printed and saved. Use <tt class="COMMAND">newfs</tt> to re-create the file systems.
Re-mount the root partition of the floppy read-write (<tt class="COMMAND">mount -u -o rw
/mnt</tt>). Use your backup program and backup tapes to recover the data for this file
system (e.g. <tt class="COMMAND">restore vrf /dev/sa0</tt>). Unmount the file system
(e.g. <tt class="COMMAND">umount /mnt</tt>). Repeat for each file system that was
damaged.</p>

<p>Once your system is running, backup your data onto new tapes. Whatever caused the
crash or data loss may strike again. Another hour spent now may save you from further
distress later.</p>
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