Bootloader unlocking

The bootloader is a special program on a device that loads the operating system when the device is turned on. Bootloaders are typically set by the manufacturer and shipped to retailers and consumers in a "locked" state, in which the bootloader can only load the manufacturer's operating system (OS). Unlocking a bootloader disables the checks that force the use of a particular operating system, allowing the use of third-party operating systems such as Linux or Android without Google software.

Unlocking the bootloader of a smartphone enables the user to install alternative operating systems, colloquially known as "custom ROM".^[1]

Difference from Rooting

Rooting a device allows users to bypass OS restrictions while the device is running. Conversely, bootloader unlocking allows rewriting the storage drive where the OS is installed, but does not grant any further abilities after the OS is loaded. Bootloader unlocking, however, allows users to enable root access by either manually editing the loaded operating system or using an app to do so automatically.^{[citation needed (12 Mar 2026)]}

See Jailbreak for more info.

Most custom ROMs do not contain any components that send data to manufacturers, Google, or their partner companies.^[2] In some cases, they even contain components that prevent individual apps from doing so, such as:

• /e/'s Advanced Privacy
• CalyxOS's Datura Firewall
• iodéOS's blocker

Default Android systems deeply integrate with Google Play Services (and Google Mobile Services (GMS)). This is a system process that requires access to files, contacts, storage, call logs, SMS messages, location, camera, and microphone. Without this process running, many apps will not function.^[3] Alternative systems avoid this process entirely, or use a privacy-preserving workaround such as:

• GrapheneOS's Sandboxed Google Play
• MicroG^[4]
• Unified Push

Most custom ROMs do not contain bloatware and can thus be used to extend the longevity of phones that have become unusable due to later updates requiring more performance and storage. Especially on low-end phones, these updates often exhaust the built-in storage after as little as two years.^{[citation needed]} This renders the device slow and unstable, without room for user data. Custom ROMs are typically much smaller than the manufacturer's software.^{[citation needed]} Consequently, many old phones can run even faster with a custom ROM than they did when new, extending their useful lifespan.^{[citation needed - Low verifiability (12 Mar 2026)][5][6]}

Low-end devices usually receive only a few years or even months of security updates.^[7] Since most custom ROMs are built by the open-source community, installing one allows users to receive security updates for the Android system and default components, such as web browser engines and PDF readers, as long as custom ROMs are developed. Popular custom ROMs such as LineageOS and GrapheneOS have lasted over 10 years, and are open source, allowing anyone to maintain them and continue their development. ^[8][9]

Some applications cannot be easily removed in the default OS. A custom ROM gives users complete control over what is in their operating system, such as preinstalled apps and system themes. ^{[10][citation needed]}

A locked bootloader protects the device from an Evil Maid Attack. This attack occurs when a person with physical access to a device manipulates the operating system, typically when the device is left unattended or when handed over for inspection by authorities. Locking the bootloader ensures that the operating system remains intact and cannot be altered from the state in which the manufacturer released it.^{[citation needed (12 Mar 2026)]}

Some devices hold DRM keys, which are deleted when the bootloader is unlocked. Other devices go so far as to wipe proprietary drivers. ^[11] This allows manufacturers to force the use of their software and maintain control over devices, preventing unsupported devices from receiving updates, removing some apps and services, and bypassing other DRM, such as the iPhone's component DRM.^{[citation needed (12 Mar 2026)]}

Some mobile carriers have completely restricted the unlocking of bootloaders on specific models of cellphones that they sell to prevent bypassing carrier restrictions.^{[citation needed]}

Unlocking the bootloader is possible on some, but not all, Android devices.

Apple products such as iPhones do not support unlocking the bootloader or verifying the authenticity of the firmware and bootloader with digital signatures, making bootloader unlocking difficult.^[12] Instead, People jailbreak their iPhones using 3rd party software.^[13][14]

These include, but are not limited to:

• GrapheneOS
• IodéOS
• /e/OS
• LineageOS
• CalyxOS

• AOSP (Android Open Source Project) , also known as "stock" Android.^[15][2]