saturday, May 27, 2017 - 20:45

Assigning folders in the Android file system

To sort and move files on the internal drive, you need to know the purpose of the folders in the file system. In the article we will learn in detail in which folders user information is stored, and where data is the application, the removal / relocation of which will disrupt the work of installed programs.

Android Memory Sections

Since Android is a Linux-based OS, the file system includes six partitions. By default, the user can only access the internal memory section - data. Access or modification of files from other partitions without ROOT rights is prohibited.

• Boot Inside the folder is stored the system kernel, virtual disk and other files needed to launch a mobile device.
• System. Used to store operating system files, user interface graphics and pre-installed programs.
• Recovery. Folder with backup data for recovery and system boot.
• Data. The internal memory section where user information is stored: media files, games, applications, etc.
• Cache The folder is necessary for the system to temporarily store frequently used data and application components.
• Misc. It stores data on the system settings, user-defined configurations, network parameters of the cellular operator. Also, various parameters that are displayed in the system in the form of switches.

Folders in the data section

• Android Inside there are two folders - obb and data. The first stores the cache of games, the second data is installed applications. Deleting or moving folders will result in the loss of settings and incorrect operation of programs.
• Alarms, Ringtones, Notifications. Folders are designed to store sounds and musical compositions, for alarm clocks, ringtones and notifications. The placed files in these folders will be displayed in the system when selecting melodies. Otherwise, the sounds will have to choose using the player or file manager.
• Bluetooth The folder contains files received via a wireless Bluetooth connection.
• DCIM. The folder stores photos and videos taken with the standard application. If “MicroSD file storage” is selected in the program settings, then the footage will go to the DCIM folder on the external drive.
• Documents. A place to store text documents.
• Downloads. Download folder. Downloaded files via Chrome or other Google services automatically fall into this section. Third-party applications also save files in the Downloads folder, but more often use their own folders.
• Pictures, Music, Movies, Video. Folders for storing multimedia files that are used by default players. Placed there music or video will automatically appear when you start the corresponding application. Otherwise, you must specify the path for the files manually. Also in the Pictures folder are screenshots.
• Podcasts. The folder is used by applications in the case of listening to podcasts.

It should be noted, not used folders remain empty. Third-party applications often create their own directories to store temporary and permanent files, such as Viber or Titanium Backup.

Conclusion

Deleting any folder or file in the internal memory section results in only the loss of some data. Therefore, to disrupt or damage a mobile device by such actions will not work. The next time you launch it, the application will download and write the missing files.

But deleting / moving files outside the data section is guaranteed to violate the integrity of the system and make the device unstable. In this case, help reset to factory settings or re-record firmware. Therefore, in the presence of ROOT rights, it is not desirable to touch the files of the system partition.

It is difficult to find constructive and competently submitted information about the device of the Android operating system on the Runet’s open spaces. For the most part, the information is fragmented and incomplete, there is no introduction to basic concepts, which makes it difficult for newcomers to understand and understand. In the absence of basic knowledge of the device and the algorithm of the Android operating system, it is impossible to debug or customize the firmware, to develop under the Android OS. This is what prompted me to write this article, in which I will try, in a simple and understandable language, to bring "complex" things.

The material is directed, first of all, to the study of ordinary users and is presented as an introductory excursion into the world of Android operating systems. Therefore, there will be presented compressed and superficial information without technical indentations and nuances. This material will be useful to anyone who is engaged in flashing and customizing firmware, developing under the Android OS, repairing mobile computer systems and the average user to better understand the principles of operation and capabilities of their Android.

Android internal memory partitions

The internal memory of the device on the android is divided into several logical disks (partitions). We give the classic markup of memory:

Bootloader  - here is a program (bootloader) that allows you to run the Android operating system, Recovery and other service modes.

Recovery  - as the name implies, there is an engineering menu of recovery or simply Recovery.

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

System  - the system partition, in which there are all necessary for the Android OS, files, it is like the Windows folder on your C: \\ drive (hereinafter, we will associate with Windows)

Data  - a section for installing applications and storing their data. (Program files)

User  - this is a well-known sdcard or, more simply, a place for user files (My Documents). Here we are forced to retreat, because The placement of this section has several options:

• The partition is not in the internal memory, and instead it uses an external drive - the most popular option. (pic. 1)
• In devices with large built-in memory, this section is seen as a sdcard, and the external memory card is seen as a sdcard2 or extsd (there may be other variants of the name). Usually found on devices with Android 3.2. (Fig.2 Option 1)
• This option has replaced the previous version, along with Android 4.0. The User section was replaced with the media folder on the Data section, which allowed us to use all the memory available to the user for installing programs and storing data, and not the amount allocated to us by the manufacturer. In other words, sdcard and data are one. (Fig.2 Option 2)

Now that we know what and where is located, let's find out why it is there and how this information can be useful to us.

Let's start with the bootloader. This is the bootloader that launches Android, recovery, etc. When we press the power button, the bootloader starts and, if there are no additional commands (the keys are held down), it starts the boot boot. If the key combination was clamped (it has its own for each device), it starts, depending on the command, recovery, fastboot or apx. The figure below clearly shows what the Bootloader starts and how the sections are interconnected.

As can be seen in Figure 3, the Recovery section does not affect the download of the Android OS, but why is it needed then? Let's try to figure it out.

Recovery (recovery) is essentially a small utility on the Linux kernel and is loaded regardless of Android. Its regular functionality is not rich: you can reset the device to the factory settings or update the firmware (previously downloaded on the sdcard). But, thanks to the craftsmen, we have modified recovery, through which you can install modified (custom) firmware, customize android, create backup copies and much more. The presence or absence of recovery, as well as its version does not affect the performance of the Android OS (a very common question on the forums).

Particularly attentive readers might notice in Figure 3 a certain Fastboot. This is an interface for working directly with internal memory partitions, using the command line. Through it, you can flash the recovery, the kernel or the new firmware version, or format (delete all the information) this or that section.

Since we are talking about interfaces, I want to talk about another, quite well-known, adb (android debugbridge). This is the so-called debugging mode and it is named so for a reason - through it you can monitor the work of both the system as a whole and individual applications. But that's not all, with adb you can get full access to the file system of the device and change the system files or extract important information when your device is frozen on the download. I will not describe all the functions of the debug mode. My goal is to convey general information, not a detailed overview of the functions of a particular regime.

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

Press the power button - the Bootloader starts up, which loads the Kernel (boot), it, in turn, starts the system (System), well, and it already loads the programs (data) and the user space (user). (Pic 3)

Now let's go to the root directory and look at the insides of the Android OS itself:

In this scheme we have resulted, only necessary for acquaintance, directories. In fact, there are many more of them and you will need a whole article to review only one System folder.

And so, the data folder. As you can guess from the name, it is somehow related to the data, but with what? Yes, with almost everyone, this includes data on synchronization and accounts, passwords to wifi access points and vpn settings, and so on. Among other things, you can find the folder app, data and dalvik-cache - consider their purpose:

• app - programs and games are installed here.
• data - application data, their settings, game saves and other information are stored here.
• dalvik-cache is the 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.

The System folder stores system data and everything you need for the OS to work. Let's look at some of these folders:

• 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 standard melodies of calls, notifications, alarms and interface sounds, as well as boot animation (bootanimation)
• build.prop - This file is mentioned, almost the first, in conversations and articles about fine-tuning the system. It contains a huge number of settings, such as the density of the screen, the delay time of the proximity sensor, wifi control, the name and manufacturer of the device, and many other parameters.

Root superuser rights in Android OS

As with any Linux-like system, in the Android operating system, access to system files and directories is provided with Root privileges. In this section, we decided to consider the principle of operating rights of the superuser of the Android OS, the ability to edit system files or logical partitions of the file space if you have the rights of the superuser Root.

- To know what folder is good in it, but can something be done about it?

- Yes! But we need superuser rights (root) or, if we draw an analogy with Windows, administrator rights. Initially, all devices on Android go without root rights for the end user, i.e. buying a device, we are not full-fledged owners in it. This is done both to protect against malicious programs, and from the user himself - after all, in inept hands, full access to the system can lead to the "death" of the operating system and the subsequent need to re-flash the device.

“So what's the use of such a dangerous thing?”  - you ask.

Now tell:

• The ability to backup data and restore them after flashing or accidentally deleting.
• Fine-tune the system manually or with the help of special programs.
• Remove system applications, ringtones, wallpapers, etc.
• Change the appearance of the OS (for example, display the battery charge in percent)
• Adding functionality (support for ad-hoc networks, for example)

This list can be continued for a long time, but I think these examples will be enough to give an idea of ​​the possibilities and breadth of root privileges.

- This is all great, but now any program can access the “heart” of the operating system and my data?

- Not. You decide to allow this or that application to get root access or not. For this, there is the Superuser program or its advanced sister SuperSU. Without this or a similar program, using root is not possible.

As you can see, Android is not such a complicated operating system for understanding the user. If you have previously had experience with Linux-like operating systems, you will find a lot of similarities with Android systems and this similarity is justified. The Android system is derived from and built on the Linux kernel. I hope, after reading the article, you have learned something new or received an answer to a long-interested question.

Where are the folders in Android and how to enter them?

If we use a desktop computer with Windows, then we are probably accustomed to the fact that everything in this system is distributed among the disks. For example, drive C has a system installed, and drive D is used to store personal files. Other disks can be used, for example, for removable flash drives and external hard drives (for example, Z or E).

The Android system, based on the Linux kernel, is organized in a different way. It provides a tree structure of files, the starting point of which is the root. In addition, the mobile operating system itself is very case-sensitive. So, if in Windows we cannot create ALBUM and Album folders in one place at the same time, then in Android it is quite possible.

The data section on Linux contains user data as well as personal settings, and the cache section contains temporary files, including system updates. Information about devices is stored in dev, and the files that are responsible for the IMEI ID are in efs (although the last section is not always the case). System folders are in the system. As for information about the kernel and its configuration, it is contained in the proc. We add that in order to see the root partitions under precisely such names, we will need root-rights, as well as a special file manager.

If we are interested in how to enter the folders in the android, and we do not have root-rights, you should not risk just to see the sections as it was originally presented on the Linux kernel. It is best to use one of the most common file managers like Total Commander. Through such a dispatcher, we can visually see what and where exactly is located.

How to enter the folder with the cache of games in Android?

For the game to work correctly, we can not do without a set of additional files, that is, without a cache. This is especially true for games of considerable volume with 3D graphics. Immediately after installing and opening the game, the cache starts loading over the Internet. In addition, we can download and download in advance to a mobile device by connecting it via USB. Unpack the cache using an archiver like WinRar.

We add that it is strongly recommended to load the cache over Wi-Fi. If right now we do not have access to a Wi-Fi point, however there is a stable and unlimited mobile Internet, as a last resort, you can use it, as well as an application called Reverse Tethering for Android.
We recommend that you separately read the instructions for installing the obb format cache. You can enter it usually at the following address: sdcard / Android / obb.

If we cannot find the obb folder because of its absence, we should create it ourselves. Another type of cache can be searched in sdcard / Android / data.