how to create a native daemon and run from init.rc in Android

Android’s init is located at the root of the filesystem i.e. /init and also it uses different naming conventions than normal linux init, so its advised to first try and understand the details of android init Language, from system/core/init/readme.txt you can also check in the source code you have or click the link here.

Now, if you have a compiled source code, create a directory called exampleservice inside external folder,

$ mkdir external/exampleservice

$ cd external/exampleservice

$ create an Android.mk as below,

LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_SRC_FILES := exampleservice.c
LOCAL_MODULE := exampleservice
LOCAL_MODULE_TAGS := debug
LOCAL_SYSTEM_SHARED_LIBRARIES := libc
LOCAL_SHARED_LIBRARIES := liblog
include $(BUILD_EXECUTABLE)

$ cd ../../

$ make exampleservice

Once, you compiled above code, you may get a binary in out folder at out/target/product/generic/system/bin/exampleservice or you can use a command like $ find out/ -name exampleservice to find exact location.

Now, modify init.rc as below, you can also append below code to the end of init.rc

service exampleservice /system/bin/exampleservice
user exampleservice
group exampleservice
oneshot

Boot android by pushing changed init.rc at /init.rc and exampleservice binary to /system/bin/exampleservice

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