About the android recovery mode Question 1: what's the android recovery mode? Does it run a full linux kernel?
Question 2: where the recovery.img is installed? (/somewhere_in_filesystem)
Recovery mode is used mainly by carriers/manufacturers for replacing bad firmware that causes the phone to be otherwise unbootable.  Users can install signed update.zip packages (such as OTA updates) through it as well.  It does not run a full Linux kernel.  Custom recovery modes such as Clockworkmod exist also, which allow more complex things such as full backup and restore of the device software and data.
I'm not sure where recovery.img is unpacked to, but you can let the system handle that by using the following: adb shell flash_image recovery &lt;path-to-recovery-image&gt;, where the path is normally something like /sdcard/custom_recovery.img (wherever you put the image)