How to use Runtime.getRuntime().exec("cmd")

Question

In my application I'm trying to execute a native code which is present on my SD card.

File sdCard = getExternalFilesDir(null); // directory where native file is placed
String nativeFile = "nativeFile";

String cmd = "shell /system/bin/chmod 0777 " + sdCard.getAbsolutePath() + "/" + nativeFile;
Process proc = Runtime.getRuntime().exec(cmd);

But as soon as Runtime.getRuntime().exec(cmd) is executed, it throws error:

java.io.IOException: Error running exec(). Command: [shell, /system/bin/chmod, 0777, /storage/emulated/0/Android/data/com.example.andridutilproject/files/native] Working Directory: null Environment: null

Any suggestions, how to resolve this?

Answer 1

First, you should wrap calls to exec in a try-catch-clause to catch IOExceptions.

Second, use exec(java.lang.String[]) to execute a command with parameters. For example, similar to

Runtime.getRuntime().exec(new String[]{ "shell", "/system/bin/chmod", "0777", sdCard.getAbsolutePath() + "/" + nativeFile });

Answer 2

The sdcard in an Android system is usually disabled for execution. Therefore even if you correctly execute the chmod command it will fail.

You can test that easily. Start the shell via USB (adb shell) and execute the chmod command. It will fail with an error message like "Bad mode".

Therefore you have to copy the file to a different location where you have write access and then set the executable bit on that copy. You can try to copy the file for example to "/data/local/tmp/" but I am not sure if that path is still usable.