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I could really use some advice. I started a new instance on EC2 using Amazon's AMI and during the deployment process I selected a Kernel ID of "Use Default". I then configured my server the way that I wanted to and took a snapshot of it. I then created my own AMI to create new servers with. When I try and create a new server with this AMI the server fails to start and I get the error: EXT3-fs: sda1: couldn't mount because of unsupported optional features (240).

Which appears to happen because I am selecting a kernel id of "Use default" again when building my second server. I have read that in order for this to work I need to choose the same kernel id that was used in my original server. I have deleted my original server and don't know what it was using.

What is the best process to follow in order to not have these issues? Should I choose "Use Default" for my original server? How do you know which kernel it selected? Then should I just document this and always specify this during the deployment of my next servers using my custom AMI? OR should I choose a custom kernel id during the initial build and always use this one moving ahead hoping Amazon never retires it?
Thanks for any advice!

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It's probably because the kernel in the AMI supports ext2 and ext3 by default, but not ext4. I would try creating a new instance and mounting the volume that won't boot. I'll bet it's ext4. In that case, probably the fastest way to get back up-and-running is to copy data off of that volume and onto a new one.

I always use Amazon Linux instances, and I always choose the default kernel. I haven't gotten bitten by this, but you have me thinking about when I should document the kernel ID. Hope this helps.

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Thanks for the response, its actually ext3 and ext4. I did not choose these filesystem types, they came with the Amazon core AMI that I used, which is the frustrating part. Do you know how to see what kernel is being used after my first instance has been deployed? –  roacha Nov 9 '12 at 21:02
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