[SOLVED] How can I shrink a working root file system for embedded Linux

Hello,

I have a JFFS2 root file system that takes about 20MB on the NAND flash of my ARM9 processor, and it is working fine with Linux 3.2 (Ångström distro).

I want to convert the JFFS2 into a RAM file system, but before that, I must minimize its size so that it won't make the overall kernel too large. The problem is, I don't know how to do that.

This forum thread explains the necessary components of a root file system pretty well. It suggests, for instance, that the /lib directory is needed only if the executables are linked dynamically.

I build my executable with

gcc -static ...

so I expect it to be statically linked only. When I issue the

ldd <program>.out

command, I get: "not a dynamic executable". However, if I type:

file <program>.out

I get:

ELF 32-bit LSB executable, ARM, EABI5, version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux.so.3, for GNU/Linux 2.6.16, not stripped

So does my program need any shared object in the /lib directory (like pthread, for example)?

I tried removing all shared objects in the /lib directory, which resulted in all programs (including shell commands) malfunctioning, stating that needed shared libraries are missing.

Long story short, how can I know which files in my 20-MB root file system (not just library files, but files of any kind) are expendable?

Thanks in advance,
OkCalis

Originally Posted by OkCalis ELF 32-bit LSB executable, ARM, EABI5, version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux.so.3, for GNU/Linux 2.6.16, not stripped So does my program need any shared object in the /lib directory (like pthread, for example)?

No, but as the file command shows, the shared library loader (/lib/ld-linux.so.3) is needed for your program, even though it has nothing to do.

I tried removing all shared objects in the /lib directory, which resulted in all programs (including shell commands) malfunctioning, stating that needed shared libraries are missing. Long story short, how can I know which files in my 20-MB root file system (not just library files, but files of any kind) are expendable?

Mostly by trial and error. Most of the supplied system binaries in /*bin will be shared executables so most of the basic /lib (and probably /usr/lib) libraries will be needed for them. But most savings can be made in the /usr tree (and luckily that mostly is the largest one). But then again, 20MB is already quite small, my /lib is about 250 MB

BTW: not using shared libraries will increase the size of your own executables by quite a bit, so maybe you should experiment with NOT compiling them as static executables.
One of the reasons for shared executables is that one time all functions takes up less space then all of the executables having separate copies of some of those functions.
Of course, this does depend on how many executables you build, but as most shared libraries are there anyway, why not use them?

Thanks, Ehartman, your explanation was very useful.
I'm going to remove the /bin and /sbin executables step by step until I see something goes wrong.
Also, I'll remove the "-static" option from my makefile, since it does not seem to offer any advantages.

Have a good day,
OkCalis