The three major backup programs are dump(8), tar(1), and cpio(1).
The traditional UNIX® backup programs are dump and restore. They operate on the drive
as a collection of disk blocks, below the abstractions of files, links and directories
that are created by the file systems. dump backs up an entire
file system on a device. It is unable to backup only part of a file system or a directory
tree that spans more than one file system. dump does not write
files and directories to tape, but rather writes the raw data blocks that comprise files
and directories.
Note: If you use dump on your root directory, you
would not back up /home, /usr or many
other directories since these are typically mount points for other file systems or
symbolic links into those file systems.
dump has quirks that remain from its early days in Version 6
of AT&T UNIX (circa 1975). The default parameters are suitable for 9-track tapes
(6250 bpi), not the high-density media available today (up to 62,182 ftpi). These
defaults must be overridden on the command line to utilize the capacity of current tape
drives.
It is also possible to backup data across the network to a tape drive attached to
another computer with rdump and rrestore. Both programs rely upon rcmd(3) and ruserok(3) to access
the remote tape drive. Therefore, the user performing the backup must be listed in the
.rhosts file on the remote computer. The arguments to rdump and rrestore must be suitable to use
on the remote computer. When rdumping from a FreeBSD computer to
an Exabyte tape drive connected to a Sun called komodo, use:
# /sbin/rdump 0dsbfu 54000 13000 126 komodo:/dev/nsa8 /dev/da0a 2>&1
Beware: there are security implications to allowing .rhosts
authentication. Evaluate your situation carefully.
It is also possible to use dump and restore in a more secure fashion over ssh.
Example 18-1. Using dump over ssh
# /sbin/dump -0uan -f - /usr | gzip -2 | ssh -c blowfish \
[email protected] dd of=/mybigfiles/dump-usr-l0.gz
Or using dump's built-in method, setting the environment
variable RSH:
Example 18-2. Using dump over ssh with RSH set
# RSH=/usr/bin/ssh /sbin/dump -0uan -f [email protected]:/dev/sa0 /usr
tar(1) also dates back
to Version 6 of AT&T UNIX (circa 1975). tar operates in
cooperation with the file system; it writes files and directories to tape. tar does not support the full range of options that are available
from cpio(1), but it does
not require the unusual command pipeline that cpio uses.
On FreeBSD 5.3 and later, both GNU tar and the default bsdtar are available. The GNU version can be invoked with gtar. It supports remote devices using the same syntax as rdump. To tar to an Exabyte tape drive
connected to a Sun called komodo, use:
# /usr/bin/gtar cf komodo:/dev/nsa8 . 2>&1
The same could be accomplished with bsdtar by using a
pipeline and rsh to send the data to a remote tape drive.
# tar cf - . | rsh hostname dd of=tape-device obs=20b
If you are worried about the security of backing up over a network you should use the
ssh command instead of rsh.
cpio(1) is the
original UNIX file interchange tape program for magnetic
media. cpio has options (among many others) to perform
byte-swapping, write a number of different archive formats, and pipe the data to other
programs. This last feature makes cpio an excellent choice for
installation media. cpio does not know how to walk the directory
tree and a list of files must be provided through stdin.
cpio does not support backups across the network. You can use
a pipeline and rsh to send the data to a remote tape drive.
# for f in directory_list; do
find $f >> backup.list
done
# cpio -v -o --format=newc < backup.list | ssh user@host "cat > backup_device"
Where directory_list is the list of directories
you want to back up, user@host is the user/hostname combination that will be
performing the backups, and backup_device is where
the backups should be written to (e.g., /dev/nsa0).
pax(1) is IEEE/POSIX®'s answer to tar and cpio. Over the years the various versions of tar and cpio have gotten slightly
incompatible. So rather than fight it out to fully standardize them, POSIX created a new archive utility. pax attempts to read and write many of the various cpio and tar formats, plus new formats of
its own. Its command set more resembles cpio than tar.
Amanda (Advanced Maryland Network Disk Archiver) is a
client/server backup system, rather than a single program. An Amanda server will backup to a single tape drive any number of
computers that have Amanda clients and a network connection to
the Amanda server. A common problem at sites with a number of
large disks is that the length of time required to backup to data directly to tape
exceeds the amount of time available for the task. Amanda
solves this problem. Amanda can use a “holding
disk” to backup several file systems at the same time. Amanda creates “archive sets”: a group of tapes used
over a period of time to create full backups of all the file systems listed in Amanda's configuration file. The “archive set” also
contains nightly incremental (or differential) backups of all the file systems. Restoring
a damaged file system requires the most recent full backup and the incremental
backups.
The configuration file provides fine control of backups and the network traffic that
Amanda generates. Amanda will use
any of the above backup programs to write the data to tape. Amanda is available as either a port or a package, it is not
installed by default.
“Do nothing” is not a computer program, but it is the most widely used
backup strategy. There are no initial costs. There is no backup schedule to follow. Just
say no. If something happens to your data, grin and bear it!
If your time and your data is worth little to nothing, then “Do nothing”
is the most suitable backup program for your computer. But beware, UNIX is a useful tool, you may find that within six months you
have a collection of files that are valuable to you.
“Do nothing” is the correct backup method for /usr/obj and other directory trees that can be exactly recreated by
your computer. An example is the files that comprise the HTML or PostScript® version of this Handbook. These document formats
have been created from SGML input files. Creating backups of the HTML or PostScript files is not necessary. The SGML files are backed up
regularly.
dump(8) Period. Elizabeth D. Zwicky torture
tested all the backup programs discussed here. The clear choice for preserving all your
data and all the peculiarities of UNIX file systems is dump. Elizabeth created file systems containing a large variety of
unusual conditions (and some not so unusual ones) and tested each program by doing a
backup and restore of those file systems. The peculiarities included: files with holes,
files with holes and a block of nulls, files with funny characters in their names,
unreadable and unwritable files, devices, files that change size during the backup, files
that are created/deleted during the backup and more. She presented the results at LISA V
in Oct. 1991. See torture-testing Backup and Archive Programs.
There are only four steps that you need to perform in preparation for any disaster
that may occur.
First, print the bsdlabel from each of your disks (e.g. bsdlabel
da0 | lpr), your file system table (/etc/fstab) and all
boot messages, two copies of each.
Second, determine that the boot and fix-it floppies (boot.flp and fixit.flp) 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.
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: fdisk, bsdlabel, newfs, mount, and whichever backup program
you use. These programs must be statically linked. If you use dump, the floppy must contain restore.
Third, create backup tapes regularly. Any changes that you make after your last backup
may be irretrievably lost. Write-protect the backup tapes.
Fourth, test the floppies (either boot.flp and fixit.flp 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 tar xvf /dev/sa0, you might accidentally type tar cvf /dev/sa0 and over-write your backup tape).
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.
Example 18-3. A Script for Creating a Bootable Floppy
#!/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
#
bsdlabel -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 << 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 > /mnt/sbin/init
gzip -c -best /sbin/fsck > /mnt/sbin/fsck
gzip -c -best /sbin/mount > /mnt/sbin/mount
gzip -c -best /sbin/halt > /mnt/sbin/halt
gzip -c -best /sbin/restore > /mnt/sbin/restore
gzip -c -best /bin/sh > /mnt/bin/sh
gzip -c -best /bin/sync > /mnt/bin/sync
cp /root/.profile /mnt/root
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 minimum file system table
#
cat > /mnt/etc/fstab <<EOM
/dev/fd0a / ufs rw 1 1
EOM
#
# create minimum passwd file
#
cat > /mnt/etc/passwd <<EOM
root:*:0:0:Charlie &:/root:/bin/sh
EOM
cat > /mnt/etc/master.passwd <<EOM
root::0:0::0:0:Charlie &:/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."
The key question is: did your hardware survive? You have been doing regular backups so
there is no need to worry about the software.
If the hardware has been damaged, the parts should be replaced before attempting to
use the computer.
If your hardware is okay, check your floppies. If you are using a custom boot floppy,
boot single-user (type -s at the boot: prompt). Skip the following paragraph.
If you are using the boot.flp and fixit.flp floppies, keep reading. Insert the boot.flp floppy in the first floppy drive and boot the computer.
The original install menu will be displayed on the screen. Select the Fixit--Repair mode with CDROM or floppy. option. Insert the fixit.flp when prompted. restore and the
other programs that you need are located in /mnt2/rescue (/mnt2/stand for FreeBSD versions older than 5.2).
Recover each file system separately.
Try to mount (e.g. mount /dev/da0a
/mnt) the root partition of your first disk. If the bsdlabel was damaged, use bsdlabel to re-partition and label the disk to match the label that
you printed and saved. Use newfs to re-create the file systems.
Re-mount the root partition of the floppy read-write (mount -u -o rw
/mnt). Use your backup program and backup tapes to recover the data for this file
system (e.g. restore vrf /dev/sa0). Unmount the file system
(e.g. umount /mnt). Repeat for each file system that was
damaged.
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.
