3.2. Design
Take another look at the Bootdisk-HOWTO and notice how many
utilities can be squeezed onto a 1.44M floppy. There are three things that
make this possible. One is the use of shared libraries. The second is
stripped binaries. And the third is the use of a compressed filesystem. We
can use all of these techniques to save space on our root disk.
3.2.1. Shared Libraries
First, in order to use shared libraries we will need to rebuild
the BASH shell. This time we will configure it without using the
--enable-static-link option. Once BASH is rebuilt we
need to figure out which libraries it is linked with and be sure to
include them on the root disk. The ldd command makes
this job easy. By typing ldd bash on the command-line
we can see a list of all the shared libraries that BASH uses. As long as
all these libraries are copied to the root disk, the new BASH build
should work fine.
3.2.2. Stripped Binaries
Next, we should strip any binaries that get copied to the root
disk. The manpage for strip does not give much
description of what it does other than to say, "strip discards all
symbols from the object files." It seems like removing pieces of a
binary would render it useless, but this is not the case. The reason it
works is because a large number of these discarded symbols are used for
debugging. While debugging symbols are very helpful to programmers
working to improve the code, they do not do much for the average
end-user other than take up more disk space. And since space is at a
premium, we should definitely remove as many symbols as possible from
BASH and any other binaries before we copy over them to the
ramdisk.
The process of stripping files to save space also works with
shared library files. But when stripping libraries it is important to
use the --strip-unneeded option so as not to break
them. Using --strip-unneeded shrinks the file size, but
leaves the symbols needed for relocation intact which is something that
shared libraries need to function properly.
3.2.3. Compressed Root Filesystem
Finally, we can tackle the problem of how to build a compressed
root filesystem. The Bootdisk-HOWTO suggests three ways of constructing
a compressed root filesystem using either a ramdisk, a spare hard drive
partition or a loopback device. This project will concentrate on using
the ramdisk approach. It seems logical that if the root filesystem is
going to be run from a ramdisk, it may as well be built on a ramdisk.
All we have to do is create a second extended filesystem on a ramdisk
device, mount it and copy files to it. Once the filesystem is populated
with all the files that the root disk needs, we simply unmount it,
compress it and write it out to floppy.
 | For this to work, we need to make sure the system used for
building has ramdisk support. If ramdisk is not available it is also
possible to use a loopback device. See the Bootdisk-HOWTO for more
information on using loopback devices. |
