GNU/Linux distributions have many different uses. Over the years, the
software has claimed many different roles, from the usual Internet server to
high-end animation workstations, proving itself capable of undertaking almost
any computer-related task.
One special feature of GNU/Linux--that it can run from a read-only
system--has surfaced in the last few years as LiveCDs. Though credit for the
popularization goes to the famous multimedia LiveCD Knoppix, the concept
belonged to the late 1990s. Slackware and Red Hat had always produced LiveCDs for
installations and basic troubleshooting, but the self-configuring LiveCDs
started with the Linux Bootable Business Card (BBC) and peaked with Knoppix.
LiveCDs supply users with a full-blown operating system; not only the bare-bones
command prompt, but also the eye candy GUI, a whole range of applications (more than 2GB
on a single CD), full networking support with browsers and instant messaging,
the ability to read to and write from Windows shares, and, perhaps most
importantly, easier hardware configuration.
The GNU/Linux community embraced the new LiveCD, using it in everyday tasks
including showing off to Windows users. After some time, even some Windows
admins began carrying Knoppix CDs to use in case of emergency. This was not
enough for some developers, especially those who appreciate lean and mean
systems. Thinking that 700MB is just too big, Damn Small Linux strips Knoppix
to the bare minimum and builds up from there, supplying a GUI-based,
self-configuring desktop plus troubleshooting LiveCD within just 50MB. DSL
produced the leanest, meanest Linux LiveCD.
Inspired by DSL, Feather Linux
concentrates on desktop workstations, including a media player capable of
playing everything from MP3s to DivX movies. In 64MB (14MB more than DSL), Feather also supplies more troubleshooting and emergency utilities.
With its small footprint, Feather Linux downloads in just over an hour on a
128Kbps line. It is even possible to download via a 56Kbps modem, making it the ideal
emergency LiveCD for almost everyone. Its low resource needs makes it an ideal
distro for recycling legacy PCs with modest hardware, even machines with
486-DX100 CPUs or 48MB of memory. There are also active Feather Linux forums.
To demonstrate how well Feather Linux works as a rescue CD, I'm going to pose
a common administrative problem and demonstrate how to solve it with the
LiveCD. Think of it like a MacGyver computer exercise, with a Feather CD as
the Swiss Army knife. While doing this, we will practice the Unix Way, taking
full advantage of its tools: bash, Perl, pipes, redirections, and the rest of
the arcane Unix heritage.
(For those with low bandwidth, most of the things described here are possible
not only with Feather Linux, but also with Knoppix or most of the other Linux
LiveCDs you may already have. We like the lean, mean method, but using
Knoppix would not be overkill.)
Reinstalling an OS, Not the Data
GNU/Linux systems have always provided good backup solutions. Suppose you
want to erase your Red Hat 9 partition and install Debian Woody instead. In the
common case, all you have to do is to back up /home to have all your
default userspace files and configurations. /etc and /var may
also be handy. Then install Woody.
This is the simpler of the two basic approaches.
Another approach is to back up the partition as a whole: the operating
system, the user files, and the configurations (if they are on the same
partition). In this case, whenever you want to revert to your old system, you
can restore the image.
This second scheme is more delicate. First, you need a host operating system
from which to restore the image. In fact, you may not be able to make the
snapshot easily from the live system, so it's possible you can't do this at all from
your current operating system.
Feather Linux for Snapshots
Obviously you'll have to use a boot disk or CD or another OS already
installed. That's why we have this nice, tiny Feather Linux LiveCD ready. You
also need a program to make an image from a disk and something that can restore
an image to a disk. You can use dd to do this the pure Unix Way, but Feather Linux has a wonderful disk imager called PartImage. Written by
Francois Dupoux and Franck Ladurelle, PartImage has two very nice features:
You can restore your partitions in case of any problem. It's handy if you
fear losing an NTFS partition to the newest teenage mutant RPC worm.
You can install many PCs simultaneously. If you have 50 PCs with the same
hardware, just install the first, configure it, take the image, and restore it
to the rest.
Unknowingly, you have everything ready! You can use partimage
in the traditional "restore the backup image from a network drive" way, or you
can use its client-server installation method. The fascinating thing is that the
developers of PartImage even thought of encrypting that server-client
deployment communication.
Enough theory. Let's start the first Feather Linux mission: to back up and
restore an entire partition.
Backing Up a Partition
First, boot your computer with Feather Linux. Chose the "boot from CD"
option in your BIOS, if necessary; insert the CD; and start. The boot prompt
is the regular Knoppix one with different clip art. At the prompt, I prefer to
write:
knoppix 2 toram
knoppix 2 boots Feather Linux into a black terminal screen, not
the GUI, supplying the fastest boot. toram tells Feather to copy
the disc to RAM and operate from there. This avoids the CD-ROM from spinning
whenever you start a new program. Second, it allows you to eject the Feather
CD and even burn the image to a CD. If you have more than 96MB of RAM, I strongly
advise you to use this option.
Here comes another basic problem. You have booted from Feather and will take
the backup image of the partition, but you need some place to put it. It wouldn't be very wise to put the backup into the same disk, so a better option is to
store it somewhere on the network.
The method of transfer varies; you can use SSH, FTP, or even Samba. Let's
do the hardest and presume that we have a Samba server or a native Windows
share on the network. The first step is to make a mount point:
# mkdir /root/mnt/k
Next, mount the share:
# mount -t smbfs -o username=user1,password=pass //192.168.1.190/E$ /root/mnt/k
This is the regular way to mount a windows share (E$) via Samba to the
filesystem under /root/mnt/k.
Running partimage from the shell produces something similar to the result shown in
Figure 1. From there, choose the partition from which to make the image. I
advise non-English users to use the default C locale, because I experienced
problems using the lang=tr option. This may be due to a conflict
with the Turkish locale and partimage. Otherwise, you may not be
able to use the regular arrow keys to navigate in the menus.
Figure 1. Choosing a partition to back up
After choosing the right partition, decide on the image name. Then choose
whether to back up to an image or restore an image. After the configuration, press F5 to proceed to the next screen.
Now you have the choice of a compression algorithm, as seen in Figure 2. I
prefer to use gzip or no compression. Unless you have to fit the image into a
limited space on a CD-R or such, I advise against using bzip. Though it will
bring superior compression, it may not be worth the effort, especially if the
partition has lots of multimedia files.
Figure 2.
Choosing a compression type
If you want, you can divide the image into pieces. Again, this is useful for
writing onto removable media or if the destination drive is a VFAT partition. (FAT32 has a 2GB file limit.)
The next prompt, shown in Figure 3, asks for an description of the saved
partition, and then the imaging process begins. The length of this step depends on
the size of the partition and the compression algorithm. In my tests it took
45 minutes to save the image of a 15GB NTFS partition without compression.
Figure
3. Describing the backup image
partimage can save many different partitions, including
ext2/ext3, FAT16/32, Reiserfs, JFS, HPFS, UFS, HFS, and NTFS. NTFS support is
still experimental, as the PartImage web site explains:
The NTFS (Windows NT File System) is currently not fully supported:
this means you will be able to save an NTFS partition if system files are not
very fragmented, and if system files are not compressed. In this case, you will
be able to save the partition into an image file, and you will be able to
restore it after. If there is a problem when saving, an error message will be
shown and you won't be able to continue. If you have successfully saved an NTFS
NTFS partition, you shouldn't have problems as you restore it (except in the
case of bugs). Then the best way is to try to save a partition to know if it is
possible. If not, try to defragment it with diskeeper or another tool, and try
to saving the partition again."
There is little risk; if you can take the image, you can restore it. Figure
4 shows a happy success screen.
Figure 4. A
successful backup
Command-Line partimage
You may prefer to use partimage from the command line, without the GUI. To
take an image of /dev/hda4 with compression and save it to
/root/mnt/k/imagefile, the command is:
# partimage -z1 -o -d save /dev/hda4 /root/mnt/k/imagefile
To restore the image, use:
# partimage restore /dev/hda4 /root/mnt/k/dosya
Let me remind you that if you want to restore an NTFS partition, you have to
make some adjustments after restoring and booting from the Windows boot CD.
That process is beyond the scope of this article.
If this is a Linux partition and you are using LILO as your bootloader, then
you should reinstall the LILO, booting via Feather:
# mount /dev/hda4 /mnt/new
# chroot /mnt/new
# /sbin/lilo
With this done, you can now take an image of almost any partition and
restore it. Don't forget that this is a last resort, not a regular
backup option.
KIVILCIM Hindistan
works as a full time computer security consultant with a CISSP, using Linux and Free Software as weapons of choice.
