问题2 ：安装了recovery.img的位置？ （/某个某个_in_filesystem）
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)
adb shell flash_image recovery <path-to-recovery-image>, where the path is normally something like
/sdcard/custom_recovery.img(wherever you put the image)
Recovery mode is a minimal OS that boots from another partition. It does run a Linux kernel without some display/network/3g modules. On some ROMS you can actually start adb shell while the device is in recovery mode and see the kernel running (adb shell ps)
the recovery.img image is installed in a block device (partition) usually /dev/mmcblk[x]p[y]