Android from the inside or just about complicated

\ December 18, 2012 \ \ Dreamer ... \

Introduction

Communicating on forums and being curated multiple themes, often encounter a complete lack of understanding of beginners android device. "Well, and what the average user to know?" - you might say. And here I agree with you by asking another question: "And why would a normal user reaches into the wilds of firmware, root access and system tweaks, not realizing there's nothing?". That is what led me to write this article, which I will try, simple and understandable language, communicate complicated things.

The material is aimed primarily at casual users. Therefore, there will be presented a condensed and surface information without technical recesses and nuances.



Content:

1. Sections of internal memory.
   
2. Bootloader, recovery, adb and fastboot
   
3. Internal systems.
   
4. Root.
   

1. Sections of internal memory

Internal memory devices for android divided into multiple logical disks (partition).

I will give only the main ones:



Pic.1

Bootloader - here is the firmware (boot loader), allows you to run the operating system, and other service rekaveri modes.

Recovery - as the name implies, there is established an engineering recovery menu or just rekaveri.

Boot - the heart of the Android OS, here is the core driver and the processor and memory management settings.

System - the system partition, which contains everything needed to run the Android operating system, files, this is the Windows folder on your C: \ drive (hereinafter, will be conducting association with Windows)

Data - section for installing applications and data storage. (Program files)

User - Everyone knows sdcard or, more simply, a place for the user's files (My Documents). Here I must digress, because placement of this section has several options:

Key is not in the internal memory and instead use an external drive - the most popular option. (Fig.1)
In devices with a large built-in memory, this section is seen as sdcard, and an external memory card or seen as sdcard2 extsd (there may be other embodiments of the name). Usually found on devices with Android 3.2. (Embodiment 1 Fig.2)
This embodiment replaces the previous embodiment, together with 4.0 Android. User profile folder is changed media in the Data section, allowing the user to use all the available memory for installing programs and storing data, and not the quantity, that gave us the manufacturer. In other words sdcard data and are in one piece. (Embodiment 2 Fig.2)



Pic2

2. Bootloader, Recovery, adb and fastboot

Now that we know that where there is, let's see what it's there.

Let's start withBootloader . This loader which starts Android, etc. rekaveri When we press the power button, starts the boot loader, and if there are no additional teams (squeezed keys), starts downloading boot . If it was jammed key combination (each is its own device) that starts, depending on the command, recovery, fastboot or apx. The figure below shows clearly that launches Bootloader and both sections are interconnected.



Pic.3

As seen from the figure в„–3, sectionRecovery It does not affect the loading of Android OS, but why does he need? Let's try to understand.

Recovery (Rekaveri) is essentially a small utility on the Linux kernel is loaded and not dependent on Android. Its staff is not rich functionality: You can reset the device to factory default settings or to update the firmware (pre-downloaded to sdcard). But, thanks to the folk artists, we have modified rekaveri through which you can install modified (custom) firmware, configure android, backup and more. The presence or absence rekaveri, as well as its version does not affect the performance of the Android OS (very frequent question on the forums).

Particularly attentive readers may have noticed in Figure 3 aFastboot . This interface works directly with the internal memory partitions, using the command line. Through it can be sewn rekaveri kernel or a new firmware version, or format (erase all data) or that section.

Since we were talking about interfaces, I want to tell you about another fairly well-known -adb (Android debug bridge). This so-called debug mode and named it as a reason - through it you can keep track of the work as a whole system and individual applications. But that's not all, with the help of adb can get full access to the device's file system and change system files or pull important information when your device depending on the load. All functions of the debug mode will not describe because my goal is to convey general information, and not a detailed review of the functions of a particular regime.

3. Internal systems

Having dealt with the theory, let's run the Android OS.

Press the power button - starts Bootloader, which loads the kernel (boot), it is, in turn, starts the system (System), well, it has loads the program (data) and user space (user). (Fig.3)

Now move to the root directory and look at the insides of most Android OS:



(Fig.4)

In this scheme, I brought only the necessary for information, a directory. In fact there are many more on the review of only one System Folder will need a whole article.

And so, the folderdata . As you might guess from the name, it had something to do with the data, but with what? Yes, almost all, this data synchronization and accounts, passwords for wifi access points and configure the vpn, and so on. Among other things, here you can find the folder app, data and dalvik-cache - consider their purpose:

app - here are installed software and games.
data - Here are stored application data, their settings, saves games and other information.
dalvik-cache - program cache area for the Dalvik program. Dalvik is a Java virtual machine, which is the basis for the work of programs with * .apk extension. In order to make the launch of programs faster - their cache is created.

FolderSystem It keeps the system data and everything necessary for the OS. Let's look at some of these locations:

app - here are the system applications (SMS, phone, calendar, settings, etc.), as well as applications installed by the device manufacturer (branded widgets, live wallpapers, etc.).
fonts - System Fonts
media - contains the standard ringtones, notifications, alarms and interface sounds, as well as boot animation (bootanimation)
build.prop - This file is referred to, almost the first, in conversations and articles about fine-tuning the system. It contains a huge number of settings, such as screen density, latency proximity sensor, wifi management, the name and the manufacturer of the device and many other parameters.

4. Root

- Know that what folder is fine, but can we do something about it?

- Yes! But we need superuser (root) or if we draw an analogy with Windows, Administrator rights. Initially, all devices are on Android without root access for the end user, ie, buying the device, we are not in it full-fledged masters. This is done both to protect against malware, and from the user - in fact, in unskilled hands, full access to the system can lead to the "death" of the operating system and the subsequent need for a flashing device.

"Well, what is the use of such dangerous things?" - you ask.

Now I tell:

• The ability to make backups of your data and restore them after the firmware or accidental deletion.
  
• Fine-tune the system manually or by means of special programs.
  
• Removal of system applications, ringtones, wallpapers, etc.
  
• Change the appearance of the OS (e.g., a battery charge display percentage)
  
• Adding functionality (support for ad-hoc networks, for example)
  

This list could go on for a long time, but I think that these examples will suffice for the understanding of the possibilities and the breadth of the application root privileges.

- It's great, but now, any program can access to the "heart" of OSes and my data?

- No. You decide to allow, to a particular application, to gain root access or not. To do this, there is a program Superuser or advanced nurse SuperSU. Without this, or a similar program to use root is not possible.

Epilogue

As you can see, Android is not such a complicated thing. Hopefully, after reading the article, you have learned something new or were answered long been interested in the issue.