Embedded Android

Appendix A. Legacy User-Space

As I explained in Chapter 2, despite being based on the Linux kernel, Android bears little resemblance to any other Linux system out there. Indeed, as you can see in Figure 2-1, Android’s user-space, which we explored in Chapters 6 and 7, is a custom creation of Google. Hence, if you’re familiar with “legacy” Linux systems or come from an embedded Linux background, you may find yourself reminiscing about classic Linux tools and components you’ve been using for a long time. This appendix will show you how to get a legacy Linux user-space to coexist side by side with the AOSP on top of the same Linux kernel.

Basics

To start, we need to agree on what exactly a “legacy” Linux user-space is. For the present discussion, we’ll assume we’re talking about a Filesystem Hierarchy Standard (FHS)-compliant root filesystem. As I mentioned earlier, Android’s root filesystem isn’t FHS-compliant, and it crucially doesn’t use key FHS directories such as /bin and /lib, allowing us to superimpose, side by side with it, a root filesystem that does use these directories.

Now, I’m not saying you’ll be able to use these instructions to get yourself a root filesystem that houses both the AOSP and, say, a large distribution like Ubuntu. There are a lot more details about Ubuntu as a distribution and the AOSP that you’d need to take into account than resolving how to match a few of the top-level directories of the root filesystem. Nevertheless, if you are familiar with how to create ...