Android NDK running native processes.

Question

I want to run tcpdump on the NDK using Process.start() and want to capture this output to a buffer.Can anybody show me how i can do this?Also is the process created in the same Dalvik Vm as the JNI call or is it in a different VM?

Answer 1

Running native processes is not really a supported use of the ndk, but you wouldn't be the first person to do it.

Also note that tcpdump may need to be run as root or setuid root to be useful. And you do have a version of tcpdump compiled and linked appropriately for android?

I think that you actually want android.os.Exec.createSubprocess which is um, not public, rather than Process.start. There's a right way to do it using reflection, and a wrong way to do it by copying the Exec.java (which has declarations of the native methods) into your project. You can use a pipe to recover the results, or you can launch it through the shell and redirect the output to a file which you read from java.

See the source of an android terminal emulator with a local shell option for an example of how to do it.

(Actually, I should restate this - the right way to do it is to duplicate the native functionality of the non-public Exec methods in your own jni lib, so that you are immune to changes in that non-public part of the platform).