Introducing the init programs

The three init programs that you are most likely to encounter in embedded devices are BusyBox init, System V init, and systemd. Buildroot has options to build all three with BusyBox init as the default. The Yocto Project allows you to choose between System V init and systemd, with System V init the default.

The following table gives some metrics to compare the three:

	BusyBox init	System V init	systemd
Complexity	Low	Medium	High
Boot-up speed	Fast	Slow	Medium
Required shell	ash	ash or bash	None
Number of executables	0	4	50(*)
libc	Any	Any	glibc
Size (MiB)	0	0.1	34(*)

(*) Based on the Buildroot configuration of system.

Broadly speaking, there is an increase in flexibility and complexity as you go from BusyBox init to systemd.