adb remount
adb shell "echo 'boot-recovery ' > /cache/recovery/command"
adb shell "echo '--update_package=/sdcard/update.zip' >> /cache/recovery/command"
adb remount
adb shell "echo 'boot-recovery ' > /cache/recovery/command"
adb shell "echo '--update_package=/sdcard/update.zip' >> /cache/recovery/command"