执行 shell 命令

Question

I'm having some trouble getting my app to execute that command, it asks for root access but does not run the kill $(pidof cameraserver) part.

If I run kill $(pidof cameraserver) from the terminal on my phone it works, but not when I hit the button on my app.

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Button action = findViewById(R.id.buttonAction);

    action.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            try {
                Process process;
                Process secondProcess;
                process = Runtime.getRuntime().exec("su kill $pidof(cameraserver)");
                BufferedReader in = new BufferedReader
                        (new InputStreamReader(process.getInputStream()));
            }
            catch (IOException e){
                e.printStackTrace();
            }
        }
    });

}

Answer 1

I doubt that $(pidof cameraserver) will be expanded by the exec() method. This is a shell feature. It works in the terminal, because that's a shell. You would have to exec pidof cameraserver first and use the result of that for a second call to exec.

I also believe, that you can not use the single argument overload of exec this way. You would rather have to provide a string array that contains the command and its parameter as separate array items.

Answer 2

You're confused. Your post title is Executing shell commands , and yet what you're doing is.. not that.

Runtime.exec does not run shell commands .

It runs executables, with its own extremely crappy shell-like behaviour you should not rely on.

Just su , in bash, will apply aliases, check if it's a bash built-in, and if none of those apply, scans the PATH. Runtime.exec does almost none of those things (it kinda scans PATH, but don't rely on that). bash will expand ${pid} , * , and many other things. Runtime.exec doesn't do any of these things .

For starters, take Runtime.getRuntime().exec and put it on your verboten list. You should never ever call this method. Let it join Thread.stop and all those silent char-to-byte conversion methods that don't include a charset.

The right way to do process control is to use ProcessBuilder . This makes a lot more clear what is happening:

Java will run the exact application you provide (so, don't do su , do /bin/su ), and pass arguments verbatim with absolutely no parsing whatsoever. With the exec method you use, java will try to apply quote separation and otherwise treats spaces as separators, and does nothing more. This confusing mix of some bashisms (such as splitting your string on spaces and then treating each part as an argument) and lack of bashisms (not applying *.txt, or ${var} and friends, or supporting any of the built-ins) is just going to lead to a lot of confusion.

You have two general options:

1. Realize java just tells the OS to fire app A with argslist B with no processing whatsoever, and 'bash' is not built into the OS. There is simply no way to do any of these things directly, you have to program them. Whatever pidof does, you'd have to program it in java.

2. Start bash, not su. Then tell bash to run this command.

option 2 is possibly easier here:

ProcessBuilder pb = new ProcessBuilder();
pb.command("/bin/bash", "-c", "su kill $pidof(cameraserver)");
Process p = pb.start();

Then you're stuck trying to deal with the fact you're calling su , which goes out of its way to stop you from doing this. Having a script just casually pick up root rights is something that is just going to lead to a ton of security issues.

Find another way. For example, make a shell script that runs this command, then use some linux knowhow to give this shell SUID rights (so that it automatically and silently is run with the rights of the owner), then make it owned by root, and then use processbuilder to exec "/bin/bash" , "-c" , "/path/to/that/script" . This has a chance of being safe: That shell can only be written to by root (make sure of that,), and thus you have now decided, as operator of the hardware you run this on. that this specific job is acceptable even for non-root users to run.

NB: If you've configured your su to just let this happen without asking for passwords, go back. Undo that mistake. Keep your system safe. root access is hidden behind a few doors for a reason. Stop replacing the locks on your safe with paper and sticks.

Answer 3

I finally fixed the issue, I have my phone rooted with Magisk so all i had to do was use their 'su' file, I'm new to Java and android development so i don't really know how to explain myself in proper terms but here's the code:

ProcessBuilder pb = new ProcessBuilder();
                pb.command("/sbin/su", "-c","pkill cameraserver");
                Process p = pb.start();

This limits the user to use Magisk, but since this is for personal use it wont matter much.

Thanks to EricSchaefer and rzwitserloot for their knowledge and help.