Develop Reference

Why is the output of an adb command different when run from adb shell and run from Android Application?

I am relatively new to android and I just came across adb shell commands which provide a lot of useful things. My issue is that when I execute the command "top -bn1" using adb shell from terminal it gives me a bunch of processes with users - root, system and other users. But when I run the same command from an application using Runtime.getRuntime().exec("top -bn1") the ouput is totally different and only processes for a particular user are displayed.
Here is the adb output -
And here is the code in the app and its output -
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
process = Runtime.getRuntime().exec("top -bn1");
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(process.getInputStream()));
String msg = bufferedReader.lines().collect(Collectors.joining("\n"));
Log.d("Data", msg);
} catch (IOException e) {
e.printStackTrace();
}
}
Can somebody please explain -
Why is there a difference in the outputs as such?
How can I get the entire output by running the command from application?
What all requirements are there for the same?

adb shell is member of a lot of groups so it has a lot of privileges. It is not root, but it is as close as it gets. You can see the list of groups that the shell user is added by running id command from the terminal or check out this answer. On the other hand, your application runs in a sandbox and have very limited privileges. That's why you see a limited info when you run a command from the app code.
If you want to have unlimited access to the system from within your application, you need to request root access. You can do that by running the su command in a rooted phone:
Runtime.getRuntime().exec("su");

Complete terminal control on android

I have been trying to run a few Linux commands on my android phone with
Process process = Runtime.getRuntime().exec(COMMAND);
BufferedReader in = new BufferedReader(new InputStreamReader(process.getInputStream()));
And noticed that I can only run specific commands and get the proper output even if the device is rooted with SuperSU (I have also tested it with a device without SuperSU on it).
For example, if I run ls and try to put it on a screen (through a TextView) as follows:
public void onBtnClick(View view) {
try {
EditText commandLine = findViewById(R.id.commandText);
Process process = Runtime.getRuntime().exec(commandLine.getText().toString());
BufferedReader in = new BufferedReader(new InputStreamReader(process.getInputStream()));
((TextView) findViewById(R.id.mainTextView)).setText(((TextView) findViewById(R.id.mainTextView)).getText() + "\n" + in.readLine());
commandLine.setText("");
} catch (IOException e) {
e.printStackTrace();
}
}
the output is acct which makes sense.
But on the other hand, if lets say I run pwd it gives me the following error:
W/System.err: java.io.IOException: Error running exec(). Command:
[pwd] Working Directory: null Environment: null
I did some research online and stumbled upon Termux that can have complete control over the phone through a terminal which is exactly what I'm looking to make (for my own learning and testing purposes).
And although it's just an emulator it can do exactly what I want but the only problem is that it requires I input the commands through the terminal.
What I'm here for is to sort of replicate what Termux does for myself so that I could run Linux commands properly from the Java code of the application, not requiring the user to actually input commands.
Can anyone help me with where to start and the basics of running those commands properly on my device?

Termux states that it doesn't work as a traditional Linux bash does since it sets its own virtual-ish environment when first setting up in its data directory in /data/data/com.termux/files/usr see here and here
Also, according to the official android docs, the exec(command) method,
Executes the specified string command in a separate process.
This is a convenience method. An invocation of the form exec(command)
behaves in exactly the same way as the invocation exec(command, null,
null).
So if it's a separate process, when executing a command, it will run it inside that process' directory (Each process in Linux gets its directory and is assigned an PID which os uses). So what the ls command gives you is simply whatever's inside that process' directory. You should be somewhere like /proc/31415/ and there's only a acct file (cgroup in regular Linux).
What you should be doing is running the command inside a directory by declaring it when invoking getRuntime().exec() see the link above to find the right one you'll need. I'd suggest using the override which handles all the parameters.
You'll need something like this:
String[] cmd = {"mkdir", "testDir"};
File env = new File(getFilesDir().getAbsolutePath());
Runtime.getRuntime().exec(cmd, null, env);
Also, it doesn't hurt to take a look at Termux's installer code (exec(). It'll give you a good overlook to setting up your environment as well as working with basic commands.
Also, I think you've done it already but double check to make sure that you're requesting WRITE_EXTERNAL_STORAGE permission for your application.

How to run root commands from Android application?

I want to write an application which roots the device on which it is installed, I mean by installing this app you will be able to root your device without a computer, just like the app in the following link,
http://www.kingoapp.com/root-tutorials/how-to-root-android-without-computer.htm
I've searched a lot on how to do that using Java code for Android devices, but there was no clear solution to me. Based on my research, I think we need the following steps:
1- Being able to use shell commands in Android using Runtime.getRuntime().exec();
2- Executing a command that gains root privileges (I think su, but this needs a rooted device to be executed).
3- Initiate a root command that will root the device.
I couldn't find a code explanation on how to do the steps above. I want to understand this process first, the commands that can be used in it, then I want to try to implement it by myself. Since there are many apps on the store that offer this feature, then implementing it must be feasible.
Could anyone please explain to me how to implement this process?
Also, is there a possibility to write a code for the opposite process, which is unrooting the device?
Any help is appreciated.
Thanks.

To run root commands, you have to use the following format:
public void RunAsRoot(String[] cmds){
Process p = Runtime.getRuntime().exec("su");
DataOutputStream os = new DataOutputStream(p.getOutputStream());
for (String tmpCmd : cmds) {
os.writeBytes(tmpCmd+"\n");
}
os.writeBytes("exit\n");
os.flush();
}
where you pass in an array of strings, each string being a command that needs to be executed. For example:
String[] cmds = {"sysrw", "rm /data/local/bootanimation.zip", "sysro"};

Remount Android file system through java

I need to remount android file system as read write instead of read only. I know how to do it through command prompt and also how to go about it for application development.
But I am into tweaking the android source code and there if I use
Process proc=Runtime.getRuntime.exec("su");
it doesnot work. Therefore I need to use android.os.process object for the same and I am stuck here can anybody help me with it.

Try this code to get superuser access (you'll need a rooted phone with superuser installed):
try {
// Perform su to get root privledges
Process p = Runtime.getRuntime().exec("su");
DataOutputStream os = new DataOutputStream(p.getOutputStream());
os.writeBytes("<..... here you may write commands ....>\n");
// Close the terminal
os.writeBytes("exit\n");
os.flush();
} catch (IOException e) {
toastMessage("not root");
}
Once you have superuser access, you may start adbd listening on some TCP port using:
setprop service.adb.tcp.port 5555
adbd &
setprop service.adb.tcp.port -1
Open a TCP connection to the selected port and issue remount command.

Actually, it's difficult to understand what are you going to do. But if you're tweaking android sources (aosp) then it's will be easier for you to modify init.rc (which is under system/core/rootdir) file to get system image rw. If you want to change the state during the runtime you need to create your own native application (for instance, look into the run-as command), change inside it the uid of the process, make it as suid, embed it into the sources, and call it from your application.

android : how to run a shell command from within code

I am trying to execute a command from within my code,
the command is "echo 125 > /sys/devices/platform/flashlight.0/leds/flashlight/brightness"
and I can run it without problems from adb shell
I am using Runtime class to execute it :
Runtime.getRuntime().exec("echo 125 > /sys/devices/platform/flashlight.0/leds/flashlight/brightness");
However I get a permissions error since I am not supposed to access the sys directory.
I have also tried to place the command in a String[] just in case spaces caused a problem but it didn't make much differense.
Does anyone know any workaround for this ?

The phone needs to be rooted, afterwards you can do something like:
public static void doCmds(List<String> cmds) throws Exception {
Process process = Runtime.getRuntime().exec("su");
DataOutputStream os = new DataOutputStream(process.getOutputStream());
for (String tmpCmd : cmds) {
os.writeBytes(tmpCmd+"\n");
}
os.writeBytes("exit\n");
os.flush();
os.close();
process.waitFor();
}

If you're just trying to set brightness, why don't you do so through the provided API (AKA, is there a reason you are trying to do it the way you are).
int brightness = 125;
Settings.System.putInt(
ftaContext.getContentResolver(),
Settings.System.SCREEN_BRIGHTNESS,
brightness);

Agreed you probably need to root the phone to write to system files. I'm surprised the brightness isn't exposed through the SDK.
For details on running shell commands from code, check out this project:

You also may remout /system with permissions to write..

I think the device will need to be "rooted" for this to work. Have a search on google and see how other developers have dont this, there is no shortage of flashlight apps.

The adb shell can behave as a superuser without rooted devices.
it's a debug bridge. you can do whatever you want through it.
BUT, when your calling Runtime.getRuntime().exec, you don't have the same premissions. some shell commands aren't even available from exec.
so not only you need a rooted device, you also need su premmisions.