Citation:
This last stage is the only process that must be run on the actual device before the first boot, using the emsecondstage script which requires a working chroot environment. Typically, emsecondstage is run from some kind of minimal bootloader environment that has sufficient support for mounting subsystems like proc and filesystems like the root filesystem partition and can chroot into the root filesystem.
Je ne connais rien à l'embarqué ni à emsandbox ni à emsecondstage, mais ils disent clairement que emsecondstage doit tourner