I am trying to SSH through a jumpbox, but SSH seems to be intent on checking host keys for the jumpbox, even though I'm telling it not to, using the normal -o StrictHostKeyChecking=no -o UserKnownHostsFile=no command line options.

If I SSH directly to the jumpbox, I can have SSH ignore the error as expected:

ssh -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null -i ~/.ssh/id_jumpuser_rsa jumpuser@jumpbox

However, if I add the proxy jump option, I suddenly get the error. The error is NOT coming from the jumpbox there are no known_hosts files in any .ssh directory on the jumpbox, nor am I logging in as the jumpuser:

ssh -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null -i ~/.ssh/id_jumpuser_rsa -J jumpuser@jumpbox jumpuser@

The error message:

Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that a host key has just been changed.
The fingerprint for the ECDSA key sent by the remote host is
Please contact your system administrator.
Add correct host key in /home/user/.ssh/known_hosts to get rid of this message.
Offending ECDSA key in /home/user/.ssh/known_hosts:10
  remove with:
  ssh-keygen -f "/home/user/.ssh/known_hosts" -R jumpbox
ECDSA host key for jumpbox has changed and you have requested strict checking.
Host key verification failed.
ssh_exchange_identification: Connection closed by remote host

Where user is my regular user, not the user I am attempting to SSH as.

I have no clue what's going on here. Does SSH have a special override forcing hostkey checking for proxy jump situations? If so, it's supremely irritating, as it's going to make local VM provisioning a real pain.

3 Answers 3


The ProxyJump issues another ssh process, that does not inherit the command-line arguments that you specify on the command-line of the first ssh command. There are two possible ways out:

  • Use these options in configuration file in ~/.ssh/config -- it can save you a lot of typing too!

    Host jumpbox
      User jumpuser
      IdentityFile ~/.ssh/id_jumpuser_rsa

    and then you can connect just as ssh -J jumpbox jumpuser@

  • Use ProxyCommand option instead -- it does the same job, but more transparently so you can see what is actually going on there:

    ssh -o ProxyCommand="ssh -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null -i ~/.ssh/id_jumpuser_rsa -W %h:%p jumpuser@jumpbox" -i ~/.ssh/id_jumpuser_rsa jumpuser@

  • After mucking about with Ansible and nested quotes, I was able to get this to work correctly. I did not realize there is a subprocess, though it makes sense.
    – siride
    Mar 22, 2017 at 21:38
  • BTW, since you are an OpenSSH maintainer, do you know if this is something that could be fixed in the implementation? I don't see why those flags can't be passed on to the derived process.
    – siride
    Mar 22, 2017 at 21:50
  • 2
    It is quite new feature. I don't know about any plans to change it, but I will have a look tomorrow, if it will be useful and possible.
    – Jakuje
    Mar 22, 2017 at 21:53
  • So I tried the ssh -J jumpbox kind of approach by adding StrictHostKeyChecking no in the Host jumpbox part of my config. And I continue to get the Offending ECDSA Key in ~/.ssh/known_hosts:line# message. Could it be the jumpbox server is overriding the option? Using local ssh version OpenSSH_7.6p1, LibreSSL 2.6.2
    – dlamblin
    Feb 21, 2018 at 5:23
  • And is the jumbox hostkey changed or the target server one?
    – Jakuje
    Feb 21, 2018 at 8:22

From @Jakuje excellent answer, I made this script for generic file retrieval through a bastion host:

#!/usr/bin/env bash
set -e

ME=$(basename $0)
log_() { echo "[$ME] $@"; }


log_ Copying ${USER}@${PRIVATE_IP}:${SOURCE} to ${TARGET} via ${BASTION_USER}@${BASTION}

scp -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null \
    -o ProxyCommand="ssh -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null -l ${BASTION_USER} -W ${PRIVATE_IP}:22 ${BASTION}" \

It is useful if you are provisioning a private host inside a data center.


Being an avid Google'er, and this my first result for stackoverflow.

To ssh through a jumpbox/bastion without all the hassle, and without system modifications, etc. Then you must use StrictHostKeyChecking=no both for the proxied session, the jumper. Also you must use StrictHostKeyChecking=no in your proxy_command.

Additionally, don't get too smart for yourself and try to use UserKnownHostsFile=/dev/null for either session or proxy_command, because the your shell will lose context when piping and just fail. I didn't troubleshoot any further.

This command was discovered while cleanly downloading a file from newly minted instance to my local workstation via Terraform local-exec provisioner

ssh -i ssh_server_key.pem -o StrictHostKeyChecking=no -o ProxyCommand="ssh -o StrictHostKeyChecking=no -i ssh_server_key.pem ec2-user@<BASTION_IP> nc <INTERNAL_IP> 22" ubuntu@<INTERNAL_IP>
  • I would not recommend this. It's not necessarily, first of all. And secondly, it breaks a security feature. You also don't need to use nc now that SSH supports jumping directly. Use the accepted answer.
    – siride
    Feb 18, 2019 at 3:50

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