Boot modes - Amazon Elastic Compute Cloud
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Boot modes

When a computer boots, the first software that it runs is responsible for initializing the platform and providing an interface for the operating system to perform platform-specific operations.

In Amazon EC2, two variants of the boot mode software are supported: Unified Extensible Firmware Interface (UEFI) and Legacy BIOS.

Possible boot mode parameters on an AMI

An AMI can have one of the following boot mode parameter values: uefi, legacy-bios, or uefi-preferred. The AMI boot mode parameter is optional. For AMIs with no boot mode parameter, the instances launched from these AMIs use the default boot mode value of the instance type.

Purpose of the AMI boot mode parameter

The AMI boot mode parameter signals to Amazon EC2 which boot mode to use when launching an instance. When the boot mode parameter is set to uefi, EC2 attempts to launch the instance on UEFI. If the operating system is not configured to support UEFI, the instance launch will be unsuccessful.

UEFI Preferred boot mode parameter

You can create AMIs that support both UEFI and Legacy BIOS by using the uefi-preferred boot mode parameter. When the boot mode parameter is set to uefi-preferred, and if the instance type supports UEFI, the instance is launched on UEFI. If the instance type does not support UEFI, the instance is launched on Legacy BIOS.

Warning

Some features, like UEFI Secure Boot, are only available on instances that boot on UEFI. When you use the uefi-preferred AMI boot mode parameter with an instance type that does not support UEFI, the instance will launch as Legacy BIOS and the UEFI-dependent feature will be disabled. If you rely on the availability of a UEFI-dependent feature, set your AMI boot mode parameter to uefi.

Default boot modes for instance types

  • Graviton instance types: UEFI

  • Intel and AMD instance types: Legacy BIOS

Running Intel and AMD instances types on UEFI

Most Intel and AMD instance types can run on both UEFI and Legacy BIOS. To use UEFI, you must select an AMI with the boot mode parameter set either to uefi or uefi-preferred, and the operating system contained in the AMI must be configured to support UEFI.

Boot mode topics