Open-Source Robotics and Process Control Cookbook by Edwards Lewin

Author:Edwards, Lewin [Edwards, Lewin A.R.W.]
Language: eng
Format: epub
ISBN: 978-0-08-047981-1
Publisher: Elsevier Science
Published: 2005-06-16T16:00:00+00:00

4.4 Creating a Root Filesystem for our Embedded System

At the end of the previous section, we had the system successfully booting off the CompactFlash card, at least as far as loading the kernel. This isn’t enough, though—in order to do anything useful, we also need to build at least a basic root filesystem to live in the RAM disk.

In order to generate the root filesystem image, we need to be running with a kernel that supports the loopback device, so that we can mount and manipulate disk image files just as if they were physical storage devices. The kernel configuration I supplied for you on the CD-ROM has this support enabled. If you’re using a different computer to build your Linux software, you may need to recompile your kernel and add loopback support; you’ll find it under “Block devices” in 2.4.x kernels, or in “Device Drivers—Block devices” in 2.6.x.

Let’s first create an empty file called /initrd.img, exactly 8 MB in size, to contain our root filesystem image. We use dd(1) to achieve this (dd is one of several *NIX commands that are apparently officially depreciated, but without which people don’t seem to be able to live):

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