Embedded Linux System Development [pdf] {Zer07}

Operating systems based on the Linux kernel are used in embedded systems such as consumer electronics (i.e. set-top boxes, smart TVs, in-vehicle infotainment (IVI), networking equipment (such as wireless routers), machine control, industrial automation, navigation equipment, spacecraft flight software, and medical instruments in general).
Linux is making steady progress in the embedded arena. Because Linux is covered under the GPL, anyone interested in customizing Linux to his/her PDA, palmtop, or wearable device can download the kernel and applications freely from the Internet and begin porting or developing. Many Linux flavors cater to the embedded/realtime market.