User provided kernels

If you need a custom kernel on your Amazon EC2 instances, you can start with an AMI that is close to what you want, compile the custom kernel on your instance, and update the bootloader to point to the new kernel. This process varies depending on the virtualization type that your AMI uses. For more information, see Linux AMI virtualization types in the Amazon EC2 User Guide.

HVM AMIs (GRUB)

HVM instance volumes are treated like actual physical disks. The boot process is similar to that of a bare metal operating system with a partitioned disk and bootloader, which enables it to work with all currently supported Linux distributions. The most common bootloader is GRUB or GRUB2.

By default, GRUB does not send its output to the instance console because it creates an extra boot delay. For more information, see Instance console output in the Amazon EC2 User Guide. If you are installing a custom kernel, you should consider enabling GRUB output.

You don't need to specify a fallback kernel, but we recommend that you have a fallback when you test a new kernel. GRUB can fall back to another kernel in the event that the new kernel fails. Having a fallback kernel enables the instance to boot even if the new kernel isn't found.

The legacy GRUB for Amazon Linux uses /boot/grub/menu.lst. GRUB2 for AL2 uses /etc/default/grub. For more information about updating the default kernel in the bootloader, see the documentation for your Linux distribution.

Paravirtual AMIs (PV-GRUB)

AMIs that use paravirtual (PV) virtualization use a system called PV-GRUB during the boot process. PV-GRUB is a paravirtual bootloader that runs a patched version of GNU GRUB 0.97. When you start an instance, PV-GRUB starts the boot process and then chain loads the kernel specified by your image's menu.lst file.

PV-GRUB understands standard grub.conf or menu.lst commands, which allows it to work with all currently supported Linux distributions. Older distributions such as Ubuntu 10.04 LTS, Oracle Enterprise Linux, or CentOS 5.x require a special "ec2" or "xen" kernel package, while newer distributions include the required drivers in the default kernel package.

Most modern paravirtual AMIs use a PV-GRUB AKI by default (including all of the paravirtual Linux AMIs available in the Amazon EC2 Launch Wizard Quick Start menu), so there are no additional steps that you need to take to use a different kernel on your instance, provided that the kernel you want to use is compatible with your distribution. The best way to run a custom kernel on your instance is to start with an AMI that is close to what you want and then to compile the custom kernel on your instance and modify the menu.lst file to boot with that kernel.

You can verify that the kernel image for an AMI is a PV-GRUB AKI. Run the following describe-images command (substituting your kernel image ID) and check whether the Name field starts with pv-grub:

aws ec2 describe-images --filters Name=image-id,Values=aki-880531cd

Limitations of PV-GRUB

PV-GRUB has the following limitations:

Configure GRUB for paravirtual AMIs

To boot PV-GRUB, a GRUB menu.lst file must exist in the image; the most common location for this file is /boot/grub/menu.lst.

The following is an example of a menu.lst configuration file for booting an AMI with a PV-GRUB AKI. In this example, there are two kernel entries to choose from: Amazon Linux 2018.03 (the original kernel for this AMI), and Vanilla Linux 4.16.4 (a newer version of the Vanilla Linux kernel from https://www.kernel.org/). The Vanilla entry was copied from the original entry for this AMI, and the kernel and initrd paths were updated to the new locations. The default 0 parameter points the bootloader to the first entry it sees (in this case, the Vanilla entry), and the fallback 1 parameter points the bootloader to the next entry if there is a problem booting the first.

default 0
fallback 1
timeout 0
hiddenmenu

title Vanilla Linux 4.16.4
root (hd0)
kernel /boot/vmlinuz-4.16.4 root=LABEL=/ console=hvc0
initrd /boot/initrd.img-4.16.4

title Amazon Linux 2018.03 (4.14.26-46.32.amzn1.x86_64)
root (hd0)
kernel /boot/vmlinuz-4.14.26-46.32.amzn1.x86_64 root=LABEL=/ console=hvc0
initrd /boot/initramfs-4.14.26-46.32.amzn1.x86_64.img

You don't need to specify a fallback kernel in your menu.lst file, but we recommend that you have a fallback when you test a new kernel. PV-GRUB can fall back to another kernel in the event that the new kernel fails. Having a fallback kernel allows the instance to boot even if the new kernel isn't found.

PV-GRUB checks the following locations for menu.lst, using the first one it finds:

Note that PV-GRUB 1.03 and earlier only check one of the first two locations in this list.

Amazon PV-GRUB Kernel Image IDs

PV-GRUB AKIs are available in all Amazon EC2 regions, excluding Asia Pacific (Osaka). There are AKIs for both 32-bit and 64-bit architecture types. Most modern AMIs use a PV-GRUB AKI by default.

We recommend that you always use the latest version of the PV-GRUB AKI, as not all versions of the PV-GRUB AKI are compatible with all instance types. Use the following describe-images command to get a list of the PV-GRUB AKIs for the current region:

aws ec2 describe-images --owners amazon --filters Name=name,Values=pv-grub-*.gz

PV-GRUB is the only AKI available in the ap-southeast-2 Region. You should verify that any AMI you want to copy to this Region is using a version of PV-GRUB that is available in this Region.

The following are the current AKI IDs for each Region. Register new AMIs using an hd0 AKI.

Update PV-GRUB

We recommend that you always use the latest version of the PV-GRUB AKI, as not all versions of the PV-GRUB AKI are compatible with all instance types. Also, older versions of PV-GRUB are not available in all regions, so if you copy an AMI that uses an older version to a Region that does not support that version, you will be unable to boot instances launched from that AMI until you update the kernel image. Use the following procedures to check your instance's version of PV-GRUB and update it if necessary.