[pocket-linux] Libc.so.6 problems in Chapter 3: Maybe a solution

[Benoît Depaire]

Hi everybody, 

I've been working with the pocket linux guide for a couple of weeks
now, and have been stuck lately at chapter 3. I got the well known
boot problem with the c library (the shared library was not found).

I've been looking for a solution, reading the previous mails on this
mailing list. Ofcourse, I could have just passed this problem and go
on with chapter 4 (using the available images), but I wanted to
understand why my approach was failing.  After quite some testing, I
might have an idea what the problem is and decided that I know enough
now to proceed. However, not sure if my solution will or if I found
the real reason for the problem (I am planning to check this in the
future), I still want to share my thoughts with the rest.

In another conversation on this topic, David Horton mentioned the
possible problem was the fact that the used c library was build for a
i686 and it was used on a i386 machine. However, another person (sorry
forgot the name, and too lazy to look it up), mentioned the disks
didn't work either on the original machine used to build the disks
(and from which libc was taken).

However, I suspect that the problem is somewhere in the same line. I
suspect that the library is not "found" because it was build against a
different kernel than that used on the bootdisk. Let me tell you why I
think so:

I created a new partition on my laptop (which i use to build the
boot/root disks) and copied the rootdisk to this partition. Next I
copied the vmlinuz (for i386 machine, taken from the bootdisk image
available at the pocket linux website) to the boot directory, where
the other kernels of this machine are located. Finally, I added a new
entry in the lilo.conf file. When rebooting the machine, choosing to
load the pocket linux kernel, it failed exactly the same way as on the
machine I use the disks on. Thus, the type of machine (laptop =
pentium M 1500mhz, other machine = desktop= pentium II 233 i believe)
can not be the reason.

Next I changed the pocket linux kernel in my boot directory with the
original kernel working on this laptop. Now, the booting process looks
pretty much the same, but now the bash shell shows up. Therefore, I
believe the problem has something to do with the kernel-libc
combination.

Another indication is a certain parameter, that can be set during the
compilation of glibc.

`--enable-kernel=version'
    This option is currently only useful on Linux systems. The version
parameter should have the form X.Y.Z and describes the smallest
version of the Linux kernel the generated library is expected to
support. The higher the version number is, the less compatibility code
is added, and the faster the code gets. '

Now, you must now that I'm running a Mandrake 10.0 distro, so I can
easily believe that my c library is optimized for my kernel and fails
to work with older kernels, which i believe the kernel on the boot
disk image clearly is.

To be sure this is the real cause, one should compile the gnu c
libraries (glibc) for the older kernel and see if that works. However,
because compiling the gnu c libraries for another system than the host
system, seems rather complicated, I postpone this thill after the
pocket linux experience :).

Finally I would like to mention that the program library how-to on the
linux documentation project was a great help in understanding how the
libraries work. I could recommend this reading to anybody who wants to
know how linux finds the shared libraries.

Cheers,
Benoît

PS: An idea i had lately, maybe interesting as addition to the pocket
linux guide. Maybe it's possible to use the gmailfs (gmail account as
file system) together with pocket linux