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As Android was derived from the Linux kernel, rooting an Android device is similar in practice to accessing administrative permissions on Linux or any other Unix-like computer such as FreeBSD or OS X.
Description
Most devices running Android must be rooted in order to install custom versions of the Android system such as CyanogenMod. The stock configuration (unrooted), user-installed applications do not have direct access to the flash memory chip on the device and are not able to replace or modify the operating system itself. Rooting is also necessary for certain applications and widgets that require additional system and hardware rights such as rebooting the phone, certain backup utilities, and other access to other hardware such as status LEDs. Rooting is also needed to disable or remove manufacturer-installed applications such as City ID. Rooting the phone typically also includes installing an application called Superuser that supervises which applications are granted root rights.In contrast to iOS jailbreaking, rooting is not needed to run applications not distributed on the Google Play Store (sometimes referred to as "sideloading"). However some carriers, like AT&T, prevent the installation of applications not on the Store in firmware,[2] although the Samsung Infuse 4G from AT&T allows running applications not downloaded from the market.[3]
As of 2012 the Amazon Kindle Fire is locked to the Amazon app store instead of Google Play, and other vendors of Android devices may lock to other sources in the future. Access to alternate apps may require rooting but rooting is not always necessary. As an example, for the Kindle fire it is possible to load the "easy installer" app from the Amazon app store and then use it to "sideload" apps from any source.
One of the potential downsides to rooting is some phone makers consider it to be "modifying" the phone, which may void the warranty. However, if the phone is un-rooted before the user tries to use his or her warranty, there is no easy way for the warranty provider to know that the phone was previously rooted. The term "bricking" is used to describe a device which has had its software modified improperly to the point where it is no longer functioning.[4]
Process
The process of rooting varies widely by device. It usually includes exploiting a security weakness in the firmware shipped from the factory. For example, shortly after the T-Mobile G1 was released it was quickly 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 was leaked giving people the ability to downgrade and use the original exploit to gain root access. Once this exploit is found, a custom recovery image that does not check the digital signature of a firmware update package can be flashed. In turn, using the custom recovery, a modified firmware update can be installed that typically includes the utilities (for example the Superuser app) needed to run apps as root.The Google-branded Android devices, the Nexus One, Nexus S and the Galaxy Nexus, can have their boot-loaders unlocked by simply running the command "fastboot oem unlock" from a computer connected to the device while it is in boot-loader mode.[5] After accepting a warning the boot-loader will be unlocked so that a new system image can be written directly to flash without the need for an exploit.
Recently, Motorola, LG Electronics and HTC Corporation have added security features to their devices at the hardware level in an attempt to prevent retail Android devices from being rooted. For instance, the Motorola Droid X has a security boot-loader that will put the phone in "recovery mode" if unsigned firmware is loaded onto the device.
Industry reaction
Until recently, the response of tablet and smartphone manufacturers and mobile carriers has typically been unsupportive of third-party firmware development. Manufacturers had expressed concern about improper functioning of devices running unofficial software[6] and related support costs. Moreover, firmware such as CyanogenMod sometimes offers features for which carriers would otherwise charge a premium (e.g., tethering). As a result, technical obstacles such as locked bootloaders and restricted access to root permissions have commonly been introduced in many devices. For example, in late December 2011, Barnes and Noble and Amazon.com, Inc. began pushing automatic, over-the-air firmware updates, 1.4.1 to Nook Tablets and 6.2.1 to Kindle Fires, that removed users' ability to gain root access to the devices. The Nook Tablet 1.4.1 update also removed users' ability to sideload apps from sources other than the official Barnes and Noble app store (without modding).[7][8]However, as community-developed software has grown popular,[9][10] and following a statement by the Librarian of Congress (US) that permits the use of "jailbreaking" mobile devices,[11] manufacturers and carriers have softened their position regarding CyanogenMod and other unofficial firmware distributions, with some, including HTC,[12] Samsung,[13] Motorola[14] and Sony Ericsson,[15] even actively providing support and encouraging development.
In 2011, the need to circumvent hardware restrictions to install unofficial firmware lessened as an increasing number of devices shipped with unlocked or unlockable bootloaders, similar to the Nexus series of phones. Device manufacturer HTC has announced that it would support aftermarket software developers by making the bootloaders of all new devices unlockable.[6]
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