Hack 84. Recover from Debian Disaster 
Restore your Debian system from even the most
seemingly unrecoverable disaster.
We all make mistakes, but the worst accident
on a Debian system (or any Debian-based system, such as Knoppix) is
one that causes you to lose the contents of your
/var/lib/dpkg directory. Once that directory is
gone, you can no longer update or install software. These things
happen even to the best of us, so here's a procedure
to get your Debian system back where it was (or close), without
losing any of your data or having to reinstall all of Debian from
scratch.
OK, so you lost the /var/lib/dpkg directory.
Heck, if you had /var on its own partition, you
might have lost everything under the /var
directory. If that's the case,
you'll have a lot more work to do than restoring
your Debian package database. Unfortunately, because every system
differs, it's up to you to figure out what you need
to restore directories other than those required by Debian. At
minimum, you'll need to create the following
directories to start your recovery process. Log in as root, and run
these commands:
# mkdir -p /var/cache/apt/archives
# mkdir -p /var/cache/debconf
# mkdir -p /var/log
# mkdir -p /var/lib/dpkg/info
# mkdir -p /var/lib/dpkg/parts
# mkdir -p /var/lib/dpkg/alternatives
# mkdir -p /var/lib/dpkg/methods
# mkdir -p /var/lib/dpkg/updates
The next thing you need to do is find out what version of
libc6 you have installed. Check the
documentation for this information. For example, the first line of
the README file in the documentation directory
for libc6 often tells you the version:
# less /usr/share/doc/libc6/README
This directory contains the version 2.3.2 release of the GNU C Library.
Now fire up your favorite editor to create the
/var/lib/dpkg/status file. Enter the following
text in this file (substitute the version of your particular
libc6 for the version in our example):
Package: libc6
Status: install ok installed
Version: 2.3.2
Save this file and exit the editor.
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Be sure to press Enter after you enter the version number in this
file. A new line must appear after the version number for this
recovery method to work.
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Now you need to run the following commands. You
will get error messages and warnings, and the
apt-get dist-upgrade command will not actually
install any files, as it should. It will simply download packages.
Don't worry. Just plow through these commands,
ignoring the warnings and errors:
# dpkg --clear-avail
# apt-get update
# apt-get dist-upgrade
These commands cause your Debian system to download some critical
packages. Change to the directory where these packages are installed
and install them manually with the dpkg command.
(Ironically, Debian might complain that dpkg
isn't installed, but it works anyway.) Note the
* at the end of the package names in the following
commands. This is just a wildcard that saves you the trouble of
specifying the full package filenames. Here are the commands to
manually install the minimum required packages
you'll need for installing packages in a more
automated fashion:
# cd /var/cache/apt/archives
# dpkg -i libncurses*
# dpkg -i perl-base*
# dpkg -i libstdc++*
# dpkg -i dselect*
# dpkg -i dpkg*
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Read the error messages you encounter and be prepared to be flexible
if one or more steps give you trouble. I can almost guarantee
there's a solution to every glitch, so keep at it.
Remember that not all the error messages you see are important.
Ignore the complaints about insufficient information regarding
libc6. These error messages go away by the end
of the procedure.
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Now you're ready to get rid of that annoying message
about insufficient information regarding libc6.
Type in the following command:
# apt-get install -reinstall libc6
Finally, you can run the dist-upgrade command once
again. This causes Debian to install all the base packages required
for a bare-bones Debian distribution, because Debian
doesn't know they already exist:
# apt-get dist-upgrade
At this point, you have only rebuilt the Debian database such that it
"knows" about only the most
fundamental packages you have installed. It doesn't
know you have things such as KDE installed, or various productivity
applications. These programs are on your system and they will work,
but Debian doesn't know to upgrade them as new
versions appear. The only way to get Debian to know about the
packages you have installed is to install them again.
Don't worry. You won't have to
reconfigure the packages you reinstall. But if you want your Debian
package database to know they exist, you have to install them again.
You can install your favorite programs any way you want, but this
suggestion should make the process easier. Install the
synaptic program:
# apt-get install synaptic
Then start up a graphical desktop, and run
synaptic from a run dialog or terminal window.
synaptic is a graphical, friendly package
installer for Debian that sorts the available packages by category.
You can browse through the various categories and checkmark all the
programs you want on your system. Then have synaptic (re)install all
of them in one big batch. Voilà. You
have just recovered from one of the most disastrous types of damage
one can inflict upon a Debian system.
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