I have a running amazon ec2 linux instance associated with a keypair (p1) and I have downloaded the private key to my home desktop. Now at work, I created a keypair (p2) on my work desktop and imported the public key to Amazon via the AWS console.

At home, I want to add the public key of keypair p2 to be added to authorized_keys of my AMI instance (which I can currently access only from home). However, I forgot to bring the public key of p2 with me, so is it possible to somehow export this public key from Amazon.


5 Answers 5


Nice puzzle, thanks! Here's one answer:

  1. Start a new, temporary EBS boot t1.micro instance A, specifying keypair p2. Specify an availability zone where you have another instance B already running and to which you have access. (Start a temporary one if needed).

  2. Stop (not terminate) the instance A after it has been in the running state for a few minutes, so it has a chance to save the public key to its authorized_keys file.

  3. Detach the root EBS volume from the stopped instance A. Attach and mount it to your running instance B.

  4. Copy the public key from the mounted file system.

  5. Detach and delete the EBS volume. Terminate the temporary instance A.

  • 1
    Not sure how this actually solves the original question... it is definitely one way to deal with AWS EC2 instances if and only if you're using EBS-backed instances. Dec 19, 2011 at 22:08
  • You don't have to be using EBS boot instances except for the one time you run the temporary instance to get the public key off of it. All you want to do is get the public key which this approach does. Dec 19, 2011 at 22:18
  • 1
    If you have the private key you can regenerate the public key without going through such measures. Dec 20, 2011 at 2:06
  • 2
    Jeremy: Based on the original question, the private key is back at his office where he cannot get it. And once he gets back to the office, he can't get in to the EC2 instance because it does not have the public key for that office private key. That's why he wants to get the public key from Amazon, and the only way to do that is to start an instance with that public key. Then you have to get the public key off of that instance which is the tricky part. Dec 20, 2011 at 3:50
  • 1
    wow! lot of work to get the public key. It would have been easier for Amazon to put an "Export public key" option.
    – Jus12
    Dec 20, 2011 at 9:28

The correct ssh-keygen command is however:

ssh-keygen -y -f /path/to/privatekey > /path/to/publickey
  • This should be a comment or proposed edit on the previous answer. You are correct though.
    – JCotton
    Jan 11, 2012 at 20:52
  • You are right this should have been a comment. Unfortunately, I have not earned the privileges to comment yet :-(
    – rsmoorthy
    Jan 13, 2012 at 17:14
  • haha, well there you go. Thanks for chiming in with the correction.
    – JCotton
    Jan 13, 2012 at 17:53
  • This answer would work if he had access to the private key, but in the original question, that private key is at a different location and not accessible. Dec 20, 2013 at 20:34
  • 1
    run chmod 400 your_private_key.pem if you get "Permissions are too open error"
    – crizCraig
    Jul 19, 2014 at 0:31

I already provided one answer which uses EBS volumes to get at the ssh public key, but here's another way you can get at it by starting a temporary EC2 instance with a user-data script that sends the public key to the console output. Here are the steps:

Save the following code to a file named output-ssh-key.userdata on your local computer. DO NOT RUN THESE COMMANDS LOCALLY!

#!/bin/bash -ex
exec> >(tee /var/log/user-data.log|logger -t user -s 2>/dev/console) 2>&1
adminkey=$(GET instance-data/latest/meta-data/public-keys/ | 
  perl -ne 'print $1 if /^0=[^a-z0-9]*([-.@\w]*)/i')
cat <<EOF
SSHKEY:$(cat /home/ubuntu/.ssh/authorized_keys)
SSHKEY:Halting in 50min ($(date --date='+50 minutes' +"%Y-%m-%d %H:%M UTC"))
sleep 3000

Run a stock Ubuntu 10.04 LTS instance with the above file as a user-data script. Specify the keypair for which you want to retrieve the public ssh key:

ec2-run-instances \
  --instance-type t1.micro \
  --instance-initiated-shutdown-behavior terminate \
  --user-data-file output-ssh-key.userdata \

Keep requesting the console output from the instance until it shows your public ssh key. Specify the instance id returned from the run-instances command:

ec2-get-console-output YOURINSTANCEID | grep SSHKEY: | cut -f3- -d:

Within 2-10 minutes you will get output like this:

ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEA6rn8cl41CkzaH4ZBhczOJZaR4xBBDI1Kelc2ivzVvCB
Halting in 50min (2011-12-20 05:58 UTC)

The temporary instance will automatically terminate itself in under an hour, but you can terminate it yourself if you'd like to make sure that you aren't charged more than the two cents this will cost to run.

  • I tried this with a modern installation of awscli, and it worked with your user-data script. However I had to adapt the commands slightly. This worked for eu-west-1 region: aws ec2 run-instances --key-name mykey --instance-type t1.micro --instance-initiated-shutdown-behavior terminate --user-data file://output-ssh-key.userdata --image-id ami-c1167eb8; aws ec2 get-console-output --instance-id i-0ce56c0e02086160d; aws ec2 terminate-instances --instance-id i-0ce56c0e02086160d
    – holmb
    Feb 11, 2018 at 17:18
  • (Edited) Ok formatting is horrible here, I'll post as different answer.
    – Bernhard
    May 29, 2018 at 13:58

If you have the private SSH key you can re-generate the public key component simply by running the following ssh-keygen command:

 ssh-keygen -i -f /path/to/private-key > /path/to/public-key

That much is the simple part... The AWS console and API does not support pushing 2 keypairs when starting an EC2 instance. This is an exercise left for the system administrator to do through other means.

If you have access to the identity key already authorized you could simply perform the following ssh-copy-id command:

 ssh-copy-id -i /path/to/public-key user@EC2-instance

This will copy the given public key to the server and into the ~user/.ssh/authorized_keys file automatically for you and ensure proper permissions on the file.

The more elegant way would be to include the additional identity keys in your configuration management processes. In my case this entails adding the additional keys to the Puppet configuration for the node.

As a side note, personal preference but would would utilize a better SSH key management method than simply having to include separate keys for work and home location. As I mentioned in a previous question I maintain my keys on a USB drive that I keep with me rather than on any computer I utilize.


Another option would be to add a short script in user_data that just adds another ssh key to root:


touch ~/.ssh/authorized_keys
chmod 400 ~/.ssh/authorized_keys

echo "<KEY>" >> ~/.ssh/authorized_keys

Then you can log into the machine as root with ssh -l root -i <KEYFILE> URL and just read out the key from authorized_keys of the user ec2_user, ubuntu or however it is called.

Only thing - you need to make the machine publicly reachable, and make sure access to port 22 is possible from outside.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.