android app, libraries, and system permissions

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 System apps

A System application is NOT an application which is signed by the OS’s platform signatures.

/system is read-only without root so it prevents uninstalling applications from /system/app and /system/priv-app. Applications that are critical are put there so that they can't be uninstalled. 

/system/priv-app also allows apps installed there to use signatureOrSystem and other privileged permissions.

As for why apps might be critical, that depends on the ROM. HTC's Sense is heavily dependent on their built-in apps from what I hear, for example. They simply didn't design their UI such that it would work natively with third party apps.Updates for some system apps can be downloaded via the Play Store, such as Google Maps.

All System applications are stored in system/app directory. We from this folder we can add any application as system application and also remove.

Some application may be in system/private app or system/vendor/app directory.

when we open this app folder we get as

System Libraries

Android.mk

• 
  

This page describes the syntax of the Android.mk build file, which glues your C and C++ source files to the Android NDK.

The Android.mk file resides in a subdirectory of your project's jni/ directory, and describes your sources and shared libraries to the build system

The syntax of the Android.mk allows you to group your sources into modules. A module is either a static library, a shared library, or a standalone executable.

All system libraries are stored in system/lib directory in form of. so files are.

System Permission 

All system permission files are located in system/etc/permission directory. Here we can mention all system permission like wifi, camera etc.

Break pattern and password lock

Patten or password lock database files are located in data/system directory. 

Break pattern lock

Pattern lock database file is located with the gesture.key 

Here we are removing gesture.key database file by ADB command but your device should be rooted.

password lock

password lock database file is located with the password.key name.

Similarly, we can also remove the password.key database file by using ADB command.

Create an application as system application

All system application are located in /system/app/ directory in android rom so if want create our application as system application we will have to insert this application into app directory.

try {

Runtime.getRuntime()

.exec(new String[] { "su", "-c","mount -o remount,rw -t yaffs2 /dev/block/mtdblock3 /system/" });

Runtime.getRuntime().exec(new String[] { "su", "-c", "chmod 777 /system/" });

Runtime.getRuntime().exec(new String[] {"su","-c","cat "+ f + " > /system/app/"+name });

Toast.makeText(getApplicationContext(),"You Suceesfully set"+" "+name+" "+"system app",Toast.LENGTH_LONG).show();

} catch (IOException e) {

Toast.makeText(getApplicationContext(),"You need to root access", Toast.LENGTH_LONG).show();

}

Remove an application System application

Similarly we have to remove application form app directory.

try {

Runtime.getRuntime().exec(new String[] { "su", "-c","mount -o remount,rw -t yaffs2 /dev/block/mtdblock3 /system/" });

Runtime.getRuntime().exec(new String[] { "su", "-c", "chmod 777 /system/" });

Runtime.getRuntime().exec(new String[] {"su","-c","rm"+" system/app/"+”application name” });

Toast.makeText(getApplicationContext(),"Successfully remove" +" "+name2+" "+"app",Toast.LENGTH_LONG).show();

} catch (IOException e) {

Toast.makeText(getApplicationContext(),"You need to root access", Toast.LENGTH_LONG).show();

}

Copy system application 

Similarly we can keep backup of any system application.

try {

Runtime.getRuntime().exec(new String[] { "su", "-c","mount -o remount,rw -t yaffs2 /dev/block/mtdblock3 /system/" });

Runtime.getRuntime().exec(new String[] { "su", "-c", "chmod 777 /system/" });

Runtime.getRuntime().exec(new String[] { "su", "-c","cat"/system/app/applicationname" > /sdcard/SystemApps/"+name2 });

Toast.makeText(getBaseContext(), "SuceesFully Copy"+name2, Toast.LENGTH_LONG).show();

} catch (IOException e) {

Toast.makeText(getApplicationContext(),"You need to root access", Toast.LENGTH_LONG).show();

}