I'm trying to setup password-less SSH on an Ubuntu server with ssh-copy-id myuser@myserver, but I'm getting the error:

Warning: the ECDSA host key for 'myserver' differs from the key for the IP address ''

What's causing this, and how do I fix it? I tried deleting the .ssh directory on the remote machine, and running ssh-keygen -R "myserver" locally, but this doesn't resolve the error.

  • in my case, I change the server(ip) bind with the domain, then the The ECDSA host key for server has changed. My way is remove the related cache string about domain in ~/.ssh/known_hosts. Then the ssh works.
    – Ninja
    Commented Jul 11, 2017 at 3:59
  • I backed up the .ssh/known_hosts and let it to be recreated. Commented Apr 7, 2021 at 7:13

15 Answers 15


Remove the cached key for on the local machine:

ssh-keygen -R
  • 15
    Didn't work for me on newly install Debian server at work when SSHing in from home. Also, answer is pretty terse.
    – Krista K
    Commented Jan 16, 2014 at 7:29
  • 31
    You can update key instead of removing it. Use ssh-keyscan -t ecdsa my.server.domain >> ~/.ssh/known_hosts after that you don't need to verificate new key at first connecting to host.
    – Alex
    Commented Jul 13, 2016 at 10:01
  • 5
    For whom don't succeed to make it work: I've had registered multiples occurrences of the same IP : 1/ the said IP address (xx.xx.xx.xx), domain (tomsihap.fr), provider's given vps server address (vpsxxx.ovh.net). ssh-keygen -R for each of these did the work.
    – tomsihap
    Commented Dec 17, 2016 at 23:02
  • 4
    In case this doesn't cut it, and ssh displays the warning but doesn't show the offending line number in known_hosts, you can do ssh -v 2>&1 | grep known, then you can e.g. sed -i.orig 42d ~/.ssh/known_hosts to delete line 42 (or whatever it was)
    – unhammer
    Commented Mar 11, 2018 at 13:19
  • 2
    sometimes you have to specify the port ssh-keygen -R []:222 Commented Jul 15, 2020 at 12:43

In my case ssh-keygen -R ... didn't fix the warning. I had extra information like this:

Offending key for IP in /home/myuser/.ssh/known_hosts:8
Matching host key in /home/myuser/.ssh/known_hosts:24

I simply manually edited ~/.ssh/known_hosts and deleted line 8 (the "offending key"). I tried reconnecting, the host was permanently added, and everything was fine after that!

  • 7
    Works like a charm. Can fix this in one line with sed -e '8d' /home/myuser/.ssh/known_hosts, replacing the line number 8 and the filename with those displayed on your system. Commented Jun 22, 2017 at 14:57
  • My issue with this approach was that it's a bit confusing if the known_hosts:8 refers to a zero-indexed value or not. Good to know that it's a 1:1 mapping...
    – Daniel F
    Commented Feb 18, 2019 at 16:14
  • 3
    I noticed this happens if you use a non-standard port like 2022. In that case, you need to do ssh-keygen -R [hostname]:2022 Commented Jul 10, 2019 at 14:55
  • If I delete ~/.ssh/known_hosts, I get the message that the authenticity can't be established and "Are you sure you want to continue connecting". Answering "yes" tries and fails to connect. If I try to connect a 2nd time, I get the same ECDSA host key error I started with. Commented Oct 10, 2019 at 20:12
  • I changed ports for ssh on a router to reduce load... this fixes the message.
    – Ray Foss
    Commented Aug 28, 2020 at 19:46

I do lots of ssh-ing around between my LAN computers and my two webhosting accounts, so I've sorted out all kinds of odds and ends with SSH, including authentication problems using ssh -v to see where and what went wrong.

Having just resolved this issue and not being happy with the answers, I wanted to really know "why" myself...

The trigger for my case is: installed new server OS at work and upon installing openssh-server package, a new set of host keys were generated on work's server. Previously, all of my server OSs were Ubuntu and this time it changed to Debian (and I suspect there is a nuanced difference in permissions).

When all OSs were Ubuntu and I reinstall a server's OS, upon the first SSH in to it, I get this kind of warning, which I prefer over the silent warning above!

Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that the RSA host key has just been changed.
The fingerprint for the RSA 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 key in /home/user/.ssh/known_hosts:4
RSA host key for domain.com has changed and you have requested strict checking.
Host key verification failed.

Then I open up ~/.ssh/known_hosts on the computer initiating the ssh, delete that line, reconnect and this happens:

chris@home ~ $ ssh work
The authenticity of host '[work]:11122 ([]:11122)' can't be established.
ECDSA key fingerprint is 56:6d:13:be:fe:a0:29:ca:53:da:23:d6:1d:36:dd:c5.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '[work]:11122 ([]:11122)' (ECDSA) to the list of known hosts.
Linux rock 3.2.0-4-amd64 #1 SMP Debian 3.2.51-1 x86_64

That bit about :11122 is the port number I route SSH from on the firewall

I checked backups from a former Ubuntu server and diff'd against my new Debian install:

Ubuntu:                                            Debian:
# Package generated configuration file             # Package generated configuration file
# See the sshd(8) manpage for details              # See the sshd_config(5) manpage for details

# What ports, IPs and protocols we listen for      # What ports, IPs and protocols we listen for
Port 22                                            Port 22
# Use these options to restrict which interface    # Use these options to restrict which interfaces
#ListenAddress ::                                  #ListenAddress ::
#ListenAddress                             #ListenAddress
Protocol 2                                         Protocol 2
# HostKeys for protocol version 2                  # HostKeys for protocol version 2
HostKey /etc/ssh/ssh_host_rsa_key                  HostKey /etc/ssh/ssh_host_rsa_key
HostKey /etc/ssh/ssh_host_dsa_key                  HostKey /etc/ssh/ssh_host_dsa_key
------------------------------------------------   HostKey /etc/ssh/ssh_host_ecdsa_key
#Privilege Separation is turned on for security    #Privilege Separation is turned on for security
UsePrivilegeSeparation yes                         UsePrivilegeSeparation yes

So yes, likely, the host started using ecdsa keys recently, which based upon Ubuntu's changes lately, I would blame on an update. Ubuntu's shift away from the rock-solid linux OS I counted on is why I installed Debian this time around.

I read a security.SE q/a on ecdsa and have already removed that line from sshd_config my new Debian server. (and ran service ssh restart)

  • 3
    +1 for the nice side-by-side comparison block. Could you add a URL clariying "Ubuntu's shift away from the rock-solid linux OS" means?
    – bgoodr
    Commented Feb 9, 2014 at 16:43
  • @bgoodr it's my opinion & solely based upon setting up my own RAID fileserver several times over the past few years. :/ Crap for answer, but start googling ubuntu debian server and you'll see what I mean.
    – Krista K
    Commented Feb 10, 2014 at 7:00
  • 2
    @ChrisK You, sir, are a boss. Thanks for the detailed, yet concise, answer.
    – sargas
    Commented Aug 12, 2016 at 15:46

I added the following lines to my ~/.ssh/config, thus disabling strict host checking for all .local addresses. (with DHCP address allocation, ip addresses of my local machines are always changing)

host *.local
    StrictHostKeyChecking no

You still get the warning, though, which is fine by me.

  • 3
    Please note that ONLY DO THIS on things that you can closely monitor since this is essentialy says "I don't care who they are, so just cut the cr-p out and just connect me". Do not do this on production servers or machine that are connected to the internet. Commented Dec 3, 2020 at 4:20
  • 13
    For this use case, it isn't necessary to disable StrictHostKeyChecking. You can disable CheckHostIP, which will verify the key for the host but not for the IP address it resolves to. Commented Dec 23, 2020 at 17:20
  • @EsmePovirk CheckHostIP seems to be disabled by default in latest Ubuntu releases (that is 22.04 and later).
    – jarno
    Commented Nov 6, 2022 at 12:00
  • 1
    @EsmePovirk SSH v8.5 changed the default serverfault.com/a/1109184/333603
    – jarno
    Commented Nov 6, 2022 at 13:00
  • For some reason this didn't work for me (Windows 10, default system ssh.exe). Commented Oct 23, 2023 at 10:16

The prompt occurs every time because the IP addresses change all the time when using dynamic addressing. Try to use static IP so you only have to add the key only once.

  • 1
    Good point, did I miss where someone mentioned dynamic ips?
    – Krista K
    Commented Jan 16, 2014 at 20:13
  • Any suggestions on how to deal with the problem when you have no control over what the IP addresses are?
    – Michael
    Commented Apr 1, 2020 at 19:16
  • @Michael, what are we working with here? Do you have access to the router page? Is there a server which you can control (to act as a rendezvous point)? You can also consider about multicast DNS (mdns: Apple Bonjour / Avahi). Make a script that changes the IP address in the known_hosts file. Commented Apr 2, 2020 at 9:15
  • In a corporate environment using DHCP one often doesn't have permissions to fiddle with IP address assignments. The script idea is interesting, but I think you would need to change the known_hosts file on another machine, right? Sometimes trust only flows one direction (i.e. B trusts A to log in but not vice versa) which might make this more tricky.
    – Michael
    Commented Apr 2, 2020 at 22:46
  • Nope, only your machine needs to change the IP of the host (ssh server) in your local known_hosts file, since the keys remain the same. If you need it to be done on both the machines, just install the script in both of them. Contact me if you need more help creating a solution. Commented Apr 2, 2020 at 23:26

ssh-keygen -f "/root/.ssh/known_hosts" -R

This should replace the existing keys under known_hosts.old and create a new one. This solution worked for me in the same scenario

  • -1 as it is a duplicate of the accepted answer Commented Aug 28, 2020 at 9:14

Are you using the same user for connecting?

If you are logged into a local PC like user John and connected to the server B like user Adolf@B and everything is OK, it does not mean that everything is OK if you are logged to local PC like user Jane and connecting to the server B like user Adolf@B.

If you want to login on server B as user Beda from PC A without password, try this command, all from PC A:

ssh-keygen -t rsa

This command generates the key and stores the key in the file. Please leave passphrase empty.

ssh Beda@B mkdir -p .ssh

This command creates the directory, if they do not already exist. Otherwise, do not print an error message.

cd ~/.ssh

This command changes the directory to your users home directory ./ssh.

cat id_rsa.pub | ssh Beda@B 'cat >> .ssh/authorized_keys'

This command prints the file id_rsa.pub (your public key) into authorized_keys on the server.

IMPORTANT: Beda is your username on the server which you are connecting, B is your server IP.

Now, you can connect to the server B without a password or passphrase:

ssh Beda@B
  • 2
    Or just use ssh-copy-id to populate an authorized_keys file with your id_rsa.pub key without all the extra hassle.
    – BlakBat
    Commented Aug 27, 2018 at 11:03

At my side this happens due to something which I consider an ssh bug of newer (OpenSSH_7.9p1 and above) clients, when it tries to learn a more secure ecdsa server key where there already is an older rsa type key known. It then presents this misleading message!

I do not know a good fix for this, the only workaround I found is to remove all "good but old rsa keys" such that the client can re-learn the "new more secure ecdsa keys". So:

  1. The first step is to remove all the good old RSA keys (Warning! This loses protection against MitM):

    $ sed -i '/ ssh-rsa /d' ~/.ssh/known_hosts
  2. The second step then is to re-learn all host keys, which must be done manually by connecting to each IP again using ssh.

Edit for Windows:

  • On Windows there is no sed, hence the best fix probably is to remove the known_hosts file with

    del %USERPROFILE%\.ssh\known_hosts`
  • Warning! This loses protection against MitM until all keys are re-learned.

Here is what I observe:

$ sftp [email protected]
Connected to [email protected]

$ sftp [email protected]
Connected to [email protected].

Now try to connect to a newly introduced alias of this same already known good server:

$ sftp [email protected]
Warning: the ECDSA host key for 'gcopy.net' differs from the key for the IP address ''
Offending key for IP in /home/test/.ssh/known_hosts:45
Matching host key in /home/test/.ssh/known_hosts:44
Are you sure you want to continue connecting (yes/no)? 

Please have a look at the IP address. It's the same IP as above! So it looks like the (good) key of the (known) IP suddenly is offending itself (it isn't, as the ssh client mixes two incompatible keys, see below).

Now we try to fix it:

$ ssh-keygen -R
# Host found: line 45
/home/test/.ssh/known_hosts updated.
Original contents retained as /home/test/.ssh/known_hosts.old

Let's try again:

$ sftp [email protected]
Warning: Permanently added the ECDSA host key for IP address '' to the list of known hosts.
Connected to [email protected].

$ sftp [email protected]
Warning: the RSA host key for 'valentin.hilbig.de' differs from the key for the IP address ''
Offending key for IP in /home/test/.ssh/known_hosts:45
Matching host key in /home/test/.ssh/known_hosts:10
Are you sure you want to continue connecting (yes/no)? 

WTF? What happened here? The new fresh key learned from the server fails again? And the problem even switched sides?!?

Nope, it's not the key, nor the server. Everything is correct!

It's the ssh client which fails to verify the correct key! Entry 45 in known_hosts now carries a key of type ecdsa-sha2-nistp256 while the key, which was pulled from the server by the client, is of type rsa-sha2-512 (and therefor cannot match the other key!).

$ sftp -v [email protected]


debug1: kex: host key algorithm: rsa-sha2-512


$ sftp -v [email protected]


debug1: kex: host key algorithm: ecdsa-sha2-nistp256

Apparently the ssh client has a bug somewhere! It cannot cope with a host key existing in more than one variant! Or it falls into the trap to request an outdated variant of a key.

How to fix?

I really have no idea. This probably can only be fixed upstream.

But there is a manual but clumsy workaround:

You have to manually remove all traces of the old key of type rsa. The key in question is shown in the output, but it is not directly marked as the problem:

Warning: the RSA host key for 'valentin.hilbig.de' differs from the key for the IP address ''
Offending key for IP in /home/test/.ssh/known_hosts:45
Matching host key in /home/test/.ssh/known_hosts:10


awk 'NR==45 { print $2 }' /home/test/.ssh/known_hosts
awk 'NR==10 { print $2 }' /home/test/.ssh/known_hosts



So here the matching host key is the offending one and the offending key is the right one which must be kept! So let's remove the wrong (matching) one:

ssh-keygen -R valentin.hilbig.de
# Host valentin.hilbig.de found: line 10
/home/test/.ssh/known_hosts updated.
Original contents retained as /home/test/.ssh/known_hosts.old

Now check again:

$ sftp [email protected]
The authenticity of host 'valentin.hilbig.de (' can't be established.
ECDSA key fingerprint is SHA256:tf7lwe10C2p1lK2UG9p//m/4sUBCpX+i9k5Ub63c6Os.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added 'valentin.hilbig.de' (ECDSA) to the list of known hosts.
Connected to [email protected].

$ sftp [email protected]
Connected to [email protected].

sftp [email protected]
Connected to [email protected].

YAY! Problem finally gone. But with several 100 entries in .ssh/known_hosts, this "solution" really becomes a major PITA (and an Error Prone Security Nightmare on Elm Street. YMMV.)

  • WINDOWS 10:- Just delete contents of the file "C:\Users\svkvi\.ssh\known_hosts".
    – Vikram S
    Commented Oct 15, 2020 at 16:03
  • @VikramS Thanks, edited
    – Tino
    Commented Oct 18, 2020 at 11:08

The thread here may help.

Essentially, you want to remove both the RSA and ECDSA keys for that host, then use ssh-keyscan to put them back into your known_hosts file in a way that won't cause this conflict. It worked for me when I had the same issue.


Question: What's causing this, ...?

So the ssh server host key changed.  What caused the change?  It is hard to say.  Here are some guesses:

  • Did sshd on myserver start using ECDSA keys, so it is a new key type?
  • Was myserver recently re-installed?
  • Was sshd on myserver recently re-insalled so a new ssh host key was generated?
  • Did someone re-generate or replace the sshd host key?
  • Has the IP address of myserver changed so that a different host is answering to that IP address?

Question: ... and how do I fix it?

As others have already answered, remove the cached ECDSA host key for myserver that your account has cached.

  • 2
    Good advice, but doesn't actually answer the question. Doesn't even TRY to answer the question.
    – boatcoder
    Commented Apr 3, 2013 at 14:18

This error kept annoying me for a long time. For some reason it made a difference whether i would do a

ssh host


ssh host.domain


then pointed me to the option of changing the config file. See my script https://askubuntu.com/a/949731/129227 there for automating the process.

  • 1
    Using configuration values CanonicalizeHostname and CanonicalDomains would avoid removing strict checking and would make ssh consider host and host.domain to be same.
    – BlakBat
    Commented Nov 3, 2018 at 15:02

I fixed this on a Chromebook by uninstalling and reinstalling Secure Shell... It worked like a charm.

  • This is overkill. See a simpler solution in my answer here. Commented Jul 24, 2017 at 7:57
  • Another similar nuclear option is to rm -f ~/.ssh/known_hosts under Linux
    – Tino
    Commented Feb 23, 2020 at 1:59

Here is how to remove a known host fingerprint (from known_hosts file) on a Chrome OS:

Find the index of the offending host entry in the ssh output when the connection fails. For example in the line below offending index is 7:

Offending ECDSA key in /.ssh/known_hosts:7

Open the JavaScript console (CTRL+Shift+J) of Secure Shell window and type the following, replacing INDEX with the appropriate value (e.g. 7):


This solution was borrowed from Leo Gaggl's Blog.


The error message came with solution included in one line, just ran it and it worked like a charm.

ssh-keygen -f "/home/mymachine/.ssh/known_hosts" -R "[]:2222"

After unsuccessfully trying to disable strict mode, my solution is to clear the known-hosts file. E. g.

echo "" > ~/.ssh/known-hosts && ssh user@host

Then it will silently add a new key without errors. Whether or not something about the host changed since the last time.

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