Dev/Embedded/Rootfs/BusyBox/Example1

Minimal configuration

You can start with this example minimal config.
Some information about my choices :

• This configuration is based upon the "defaultconfig", but with many modifications (not all listed here)
• No "/usr" support (all binaries under /bin and /sbin)
• Archival utilities limited to tar with "xz" and "bz2" support
• Removed console utilities
• Removed most users handling utilities : users should be known when building the system (or added by direct editting of the files)
• Removed disk partitionning and formatting utilities save for UBIFS
• Removed runit support
• Removed all commands I never used on a full blown system

Compile using uClibc

The options selected for a minimal configuration should not impact the compilation process, unless you want a really small system, which is common when using BusyBox due to storage size constraints.
In this case using uClibc instead of the GNU libc is a good idea.
Most information about using uClibc in a cross-compilation toolchain can be found on uClibc website.
You will then need to use the cross-compilation prefix of your toolchain to build BusyBox.

With a stripped down BusyBox, you may well end up with :

Final link with: <none>

But note that in this case you'll still need the selected libc (uClibc) !

Directories and links

Here is a very simple set of directories for a configuration without "/usr", according to the minimal configuration given above :

mkdir -p dev etc lib/{modules,firmware} proc root run sys var/{log,spool/cron}

Then add some links :

ln -s run/tmp tmp 
ln -s ../run/tmp var/tmp

Libraries

As this is a very simple system the set of libraries should be very limited. You may need additional ones for your application binaries so I cannot give you a full list, but if you chose to have dynamically linked binaries (which is usually a good idea if your system has more than one or two binaries) you will always need these two :

• The dynamic linker/loader (name depending on the target architecture/triplet) : ld-linux-*.so.*
• the libc

In order to check for additional library requirements, have a look at this part in the second example below.

Once you know which libraries you need, you'll need to figure which files to put in which directory for each library.

Unless you specified an absolute or relative pathname during the linking stage of the compilation of your binaries, there is no "fixed" location for each library file, save maybe the dynamic linker/loader (ld-linux-*.so.*), which usually goes under "/lib", and the dynamic linker will end up looking for libraries in some "default" path which usually includes "/lib".

So the easy way is to create a single "/lib" directory (remember that we chose to desactivate the use of "/usr" in busybox configuration).

Bootup script

• inittab
• rc script(s) and /etc/init.d/rcS

TO BE COMPLETED

Configuration files

TO BE COMPLETED

• /etc/nologin
• /etc/securetty
• /etc/shells
• /etc/{passwd,shadow,groups}

Application binaries

TO BE COMPLETED

Application related files

TO BE COMPLETED