How to write recovery command to misc.img at Android?

cgsong

I upload custom RK3288 Android image and linux image to the Firefly for dual OS. But, there is some problem "switch system" in custom Android firmware. The custom Android image is not Firefly official image. When I connect to PC with "adb shell", "reboot recovery" command works well for switching Android to Linux. So I'd like to know how to write "recovery command" to misc.img that is /dev/block/mtd/by-name/misc at Android without PC.

cgsong

In addition, I'd like to know how to setup "switch system" at Android power menu with "(echo -n boot-recovery | busybox dd bs=16k seek=1 conv=sync; busybox dd if=/dev/zero bs=16k count=1)??> /dev/block/mtd/by-name/misc". I don't know how to put script at Android's switch system menu. Please let let me know how to put recovery command script that you told me. I'm using custom Android. So, where can I modify system file to switching system?