Alestic.com - A Personal AWS Blog by Eric Hammond

You can examine and edit files on the root EBS volume on an EC2 instance even if you are in what you considered a disastrous situation like:

• You lost your ssh key or forgot your password

• You made a mistake editing the /etc/sudoers file and can no longer gain root access with sudo to fix it

• Your long running instance is hung for some reason, cannot be contacted, and fails to boot properly

• You need to recover files off of the instance but cannot get to it

On a physical computer sitting at your desk, you could simply boot the system with a CD or USB stick, mount the hard drive, check out and fix the files, then reboot the computer to be back in business.

A remote EC2 instance, however, seems distant and inaccessible when you are in one of these situations. Fortunately, AWS provides us with the power and flexibility to be able to recover a system like this, provided that we are running EBS boot instances and not instance-store.

The approach on EC2 is somewhat similar to the physical solution, but we’re going to move and mount the faulty “hard drive” (root EBS volume) to a different instance, fix it, then move it back.

In some situations, it might simply be easier to start a new EC2 instance and throw away the bad one, but if you really want to fix your files, here is the approach that has worked for many:

The official Ubuntu images for EC2 do not allow ssh directly to the root account, but instead provide access through a normal “ubuntu” user account. This practice fits the standard Ubuntu security model available in other environments and, admittedly, can take a bit of getting used to if you are not familiar with it.

This document describes how to work inside this environment using the “ubuntu” user and the sudo utility to execute commands as the root user when necessary.