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Solved: “Instance reachability check failed” when launching an AWS EC2 instance from a custom AMI


  1. You have created your own Linux AMI from a snapshot, and
  2. You launch an EC2 instance from your AMI, and
  3. The Instance reachability status check fails when you try to start up the machine


Sample screenshot

Under these circumstances, you are unable to access the instance at all.


How to troubleshoot

  1. In the EC2 “Instances” screen, select the instance
  2. From the “Actions” menu choose “Get System Log”
  3. Scroll to the bottom and look for error messages


A solution to a common error

Under the above scenario, a common error you may receive is:

couldn't mount because of unsupported optional features (240)
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(8,1)

This is caused due to not specifying the Kernel and/or RAM ID when creating the AMI from your snapshot. To solve:

  1. In the EC2 “Instances” screen, select the instance that you wish to create an AMI from
  2. In the “Description” tab, find the Kernel ID and RAM disk ID
  3. Create a new AMI from your snapshot
  4. In the AMI creation wizard, be sure to select the Kernel ID and RAM disk ID that you got above
  5. Finish the process

The instance should start now that the AMI is properly configured.


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6 Responses

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  1. Troy says

    This was exactly my issue, and this fixed it. THANKS SO MUCH!!! Note for me, I actually didn’t have a RAM Disk ID, so chose Default.

  2. sai.pathi6 says

    I taken a space in AWS AMAZON. As per my client request, installing Active Directory in that machine. i connected remotely to that system , trying to installing active directory. But unfortunately i changed the ip address and , subnet mask and Dns in that system (where i connected in remotely , cloud system), immediately its disconnected. And i am unable to connect to it in remote. i went to that website and login , the server os is running and its hows the “instance failure” message. but its showing the os is running. How can i start my system, please help me. if any one give phone number , i will explain it.

    please help me .

  3. Orchidngo says

    Thank you so much.

    It worked for me.

  4. Filippo says

    Yes this worked perfectly! Thanks.

  5. BPD says

    If it is on the same subnet, you could try remoting to it from an instance within the same network and use the “Private DNS” as your host name.

    eg: remote into a working instance, then mstsc ip-165-87-4-245.ap-southeast-2.compute.internal

  6. Vikas Bhatt says

    Thank you soo much it fixed..i was using Paravirtual ..actually it was hvm