Learn how to organize folders and files on Android

Android is the mobile operating system most widely used in the world, known for its enormous versatility, its open source nature, and its ability to run on a multitude of devices. However, for those who want to understand how it stores and manages information, Android's file hierarchy and directory structure can seem like a real labyrinth. If you've ever wondered where Android stores your data, apps, user files, settings, or how apps interact with the system, this article will make everything crystal clear.

We are going to delve into the Android file structure, its main directories, with a pleasant and very complete approach. the organizational logic of your files and the file systems you useWhether you're a developer, an experienced user, or just curious, this guide is designed to help you master the Android file hierarchy and its inner workings once and for all.

What is the file structure in Android?

Android uses a file structure based on Linux, organized as a tree with root directory "/"This hierarchy organizes content into main and subdirectories, each with a specific purpose, ensuring both optimal system performance and data security and privacy.

Main Android directories and their function

Before we get into the technical details, it's essential to understand what each folder is for. Knowing what each system directory stores helps you understand how applications, the system, and the user interact..

• / System: The heart of the operating system. This is where the pre-installed applications, base configurations and critical elements. Sports, calculator, scoreboard, and other basic functions reside here. It's protected: it can only be modified if you have permission. root, precisely to avoid accidents or safety risks.
• /date: The "user and app drawer." This is where apps store user data, custom settings and Temporary filesEach app has its own subdirectory, preventing interference between them and increasing security.
• / cache: Space reserved for storage temporary. App cache, thumbnails, and recurring information are stored here. Deleting this directory can free up space and improve performance, as critical data is no longer stored.
• / sdcard o /storage: User area and external storage. These directories store your photos, videos, downloaded documents and other personal filesDepending on the device, /sdcard may refer to internal memory or an SD card.
• / Dev: Contains files that represent devices hardware (such as storage, sensors, etc.) It is essential for the operating system to interact with the hardware.
• / Etc: The folder of the system settings. Configure from network to options Boot. It is usually a symbolic link to /system/etc.
• / lib: It houses the system libraries, necessary for applications to function properly. Inside, /lib/modules contains the kernel modules, activated only when needed.
• /vendor: Here they are saved additional libraries and manufacturer-specific files, such as custom firmware and drivers.
• / Mnt: Classic directory for external partition mount points (USB, SD cards, etc.). It is usually a bridge to other areas where these external devices are accessed.
• / Proc: It does not contain "real" files but a representation of processes and system status in real time. Ideal for advanced diagnostics.
• / Root: Superuser directory. On Android, it's usually empty, but on traditional Linux, it serves as the root user's home directory.
• / sbin: Critical executable programs, used during boot and for advanced system operations.

Some directories like / efs (with sensitive data such as IMEI), / preload (empty on some devices) or /factory (with essential hardware information) may also appear, but their handling is delicate and they are not usually accessible to the normal user.

Digging deeper: The layers and components of Android architecture

The file structure is just one part of Android's architecture., which is made up of different layers that communicate with each other to provide stability and power:

• Linux kernel: It's the foundation. It's responsible for managing hardware access, security, memory, and file system support.
• Native Libraries: Programmed in C/C++, they provide support for multimedia, graphics and databases (e.g., OpenGL ES and SQLite). To better understand how these layers interact, you can check out (https://www.hwlibre.com/what-is-redux/).
• Android Runtime (ART): This is the current runtime environment for Android apps (previously Dalvik). Compile apps at install time, speeding up execution and saving battery.
• Application Framework: It collects all the APIs and tools that developers need to create powerful apps with access to basic services (notifications, activity management, user interfaces, etc.).
• ApplicationsBoth system apps (phone, messaging, etc.) and those downloaded by the user are located in the top layer. They interact with the system and the user, but never directly access lower layers without control.
• Hardware Abstraction Layer (HAL): It allows the software to "talk" to the hardware, acting as an intermediary. This allows Android to run on dozens of different devices.

Each layer is insulated, ensuring security and preventing problems in one from affecting the others. For example, an app cannot, except through root, modify critical files in /system or access other apps' data in /data.

Most used file systems on Android

Android can work with several file systems, each tailored to different storage types and needs:

• EXT4 (Extended File System 4): The standard on most modern Android versions. It allows you to manage large volumes of data and is optimized for speed, security and error recovery.. Supports integrity checking and automatic fault recovery.
• VFAT: Based on FAT32 but improved. It is mainly used on external partitions such as SD cards.. It supports large files and maintains compatibility with external devices and PCs.
• YAFFS2 (Yet Another Flash File System 2): Specialized in NAND flash memory, It was widely used in older devices but since Android "Gingerbread" it has been replaced by EXT4. Provides data integrity even in the event of unforeseen power outages.
• F2FS (Flash-Friendly File System): Developed by Samsung. Optimized for NAND flash memory with improved efficiency, speed, and lower wear to extend memory lifespanLess common than EXT4, but gaining ground on some premium devices.
• RFS (Robust File System): Typical of older Samsung devices. Faster than previous options, but with lower wear resistance, which could lead to data loss. There. It is currently in disuse.

File access permissions and security

One of the aspects that most concerns users is privacy. Android has been tightening permission management so that apps cannot freely access system data or other apps' files.How is this achieved?

• default permissions: Each app can only access its own space in /data and external storage if the user authorizes it. To access /system or information from other apps, it needs special permissions (root).
• Internal vs. external storage: Internal storage (/data/data/) is private to each app, is deleted when you uninstall it, and cannot be accessed by other apps. External storage (/ sdcard o /storage) is accessible after authorizing the corresponding permissions.
• Permit models: Since Android 11, apps have much more restricted access to external storage, promoting the use of private access routes and discouraging global access to all storage (except in very justified cases and with permission) MANAGE_EXTERNAL_STORAGE).
• SELinuxAndroid incorporates SELinux, an advanced security layer that prevents unauthorized access to critical system resources, even if an app attempts to bypass permission controls.

What storage options are available for developers?

When storing information, developers can choose from several options depending on the nature and purpose of the data:

• App-specific storage: Ideal for private or temporary files. The methods are used getFilesDir() o getCacheDir() for internal storage and getExternalFilesDir() o getExternalCacheDir() for private external storage of the app.
• Shared storage: Perfect for media files or documents that other apps can access. Requires permissions and is managed through Media Store or Storage Access FrameworkTo learn more about file management, check out what data management is on Android.
• Preferences and databasesFor structured or configuration data, you can use app preferences (key-value pairs) or SQLite databases using Jetpack's Room library.

The type of storage chosen depends on whether the data should be private, shared, large, temporary, etc. When the app is deleted, all the information stored in your private space disappears automatically.

Where do apps usually save their files?

Apps take advantage of Android's directory hierarchy to organize their information.:

• /data/data/: Private app directory, stores preferences, databases, and internal files.
• /sdcard/Android/data/: App-specific external storage space, useful for generated/downloaded media files or documents.
• / cache: Temporary information.
• Media Store: When the app wants to save images, videos, or audio so that the user can easily access them from the gallery or other apps.

It is recommended that developers avoid using fixed access routes, as the location may vary depending on the device and version. It's always recommended to use the APIs provided by Android.