lets all user-installed applications run privileged commands typically unavailable to the devices in the stock configuration. Rooting is required for more advanced and potentially dangerous operations including modifying or deleting system files, removing pre-installed applications, and low-level access to the hardware itself (rebooting, controlling status lights, or re-calibrating touch inputs.) A typical rooting installation also installs the Superuser application, which supervises applications that are granted root or superuser rights by requesting approval from the user before granting said permissions. A secondary operation, unlocking the device’s bootloader verification, is required to remove or replace the installed operating system.
In contrast to iOS jailbreaking, rooting is not needed to run applications distributed outside of the Google Play Store, sometimes called sideloading. The Android OS supports this feature natively in two ways: through the “Unknown sources” option in the Settings menu and through the Android Debug Bridge. However, some US carriers, including AT&T, prevented the installation of applications not on the Play Store in firmware, although several devices are not subject to this rule, including the Samsung Infuse 4G, AT&T lifted the restriction on most devices by the middle of 2011.
As of 2011, the Amazon Kindle Fire defaults to the Amazon Appstore instead of Google Play, though like most other Android devices, Kindle Fire allows sideloading of applications from unknown sources, and the “easy installer” application on the Amazon Appstore makes this easy. Other vendors of Android devices may look to other sources in the future. Access to alternate apps may require rooting but rooting is not always necessary.
Rooting an Android phone lets the owner add, edit or delete system files, which in turn lets them perform various tweaks and use apps that require root access.
Advantages of rooting include the possibility for complete control over the look and feel of the device. As a superuser has access to the device’s system files, all aspects of the operating system can be customized with the only real limitation being the level of coding expertise. Immediately expectable advantages of rooted devices include the following: Support for themes, allowing everything to be visually changed from the color of the battery icon, to the boot animation that appears while the device is booting, and more.
Full control of the kernel, which, for example, allows overclocking and underclocking the CPU and GPU.
Full application control, including the ability to backup, restore, or batch edit applications, or to remove bloatware that comes pre-installed on many phones.
Custom automated system-level processes through the use of third-party applications.
Ability to install a custom firmware (also known as a custom ROM) that allows additional levels of control on a rooted device.
Some rooting methods involve use of the command prompt and development interface called Android Debug Bridge (ADB), while other methods may use specialized applications and be as simple as clicking one button. Devices, or sometimes even different variants of the same device, can have different hardware configurations. Thus, if the guide, ROM, or root method used is for a device variant with a different hardware setup, there is a risk of bricking the device.
The process of rooting varies widely by device, but usually includes exploiting one or more security bugs in the firmware of (i.e., in the version of the Android OS installed on) the device. Once an exploit is discovered, a custom recovery image can be flashed which will skip the digital signature check of firmware updates. Then a modified firmware update can be installed which typically includes the utilities needed to run apps as root. For example, the su binary can be copied to a location in the current process’ PATH (e.g., /system/xbin/) and granted executable permissions with the chmod command. A third-party supervisor application, like Superuser or SuperSU, can then regulate and log elevated permission requests from other applications. Many guides, tutorials, and automatic processes exist for popular Android devices facilitating a fast and easy rooting process.
The process of rooting a device may be simple or complex, and it even may depend upon serendipity. For example, shortly after the release of the HTC Dream (HTC G1), it was discovered that anything typed using the keyboard was being interpreted as a command in a privileged (root) shell. Although Google quickly released a patch to fix this, a signed image of the old firmware leaked, which gave users the ability to downgrade and use the original exploit to gain root access. By contrast, the Google-branded Android phones, the Nexus One, Nexus S, Galaxy Nexus, Nexus 4, Nexus 5, Nexus 6, Nexus 5X and Nexus 6P, as well as their tablet counterparts, the Nexus 7, second-generation Nexus 7, Nexus 9 and Nexus 10, can be boot-loader unlocked by simply connecting the device to a computer while in boot-loader mode and running the Fastboot protocol with the command fastboot oem unlock. After accepting a warning, the boot-loader is unlocked, so a new system image can be written directly to flash without the need for an exploit.
In the past, many manufacturers have tried to make non-rootable phones with more elaborate protections (like the Droid X), but they are usually still rootable in some way. There may be no root exploit available for new or recently updated phones, but one is usually available within a few months.