[ubuntu] How to establish ssh key pair when "Host key verification failed"

I have set up ssh key pairs between my desktop and two servers, and from the servers to my desktop, but after reinstalling the OS on my desktop, I can't re-establish the key-pair going into my desktop by this:

mkdir ~/.ssh
chmod 700 ~/.ssh
ssh-keygen -t 
ssh-copy-id username@server

I get the following error:

(names in italics changed to protect the innocent My desktop is Ubuntu, and I can't find the answer here)

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ @ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @ @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY! 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 ab:cd:ef:gh 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:1 RSA host key for user.server has changed and you have requested strict checking. Host key verification failed.

Most likely, the remote host ip or ip_alias is not in the ~/.ssh/known_hosts file. You can use the following command to add the host name to known_hosts file.

$ssh-keyscan -H -t rsa ip_or_ipalias >> ~/.ssh/known_hosts

Also, I have generated the following script to check if the particular ip or ipalias is in the know_hosts file.

#!/bin/bash
#Jason Xiong: Dec 2013   
# The ip or ipalias stored in known_hosts file is hashed and   
# is not human readable.This script check if the supplied ip    
# or ipalias exists in ~/.ssh/known_hosts file

if [[ $# != 2 ]]; then
   echo "Usage: ./search_known_hosts -i ip_or_ipalias"
   exit;
fi
ip_or_alias=$2;
known_host_file=/home/user/.ssh/known_hosts
entry=1;

cat $known_host_file | while read -r line;do
  if [[ -z "$line" ]]; then
    continue;
  fi   
  hash_type=$(echo $line | sed -e 's/|/ /g'| awk '{print $1}'); 
  key=$(echo $line | sed -e 's/|/ /g'| awk '{print $2}');
  stored_value=$(echo $line | sed -e 's/|/ /g'| awk '{print $3}'); 
  hex_key=$(echo $key | base64 -d | xxd -p); 
  if  [[ $hash_type = 1 ]]; then      
     gen_value=$(echo -n $ip_or_alias | openssl sha1 -mac HMAC \
         -macopt hexkey:$hex_key | cut -c 10-49 | xxd -r -p | base64);     
     if [[ $gen_value = $stored_value ]]; then
       echo $gen_value;
       echo "Found match in known_hosts file : entry#"$entry" !!!!"
     fi
  else
     echo "unknown hash_type"
  fi
  entry=$((entry + 1));
done

rm -f /home/user/.ssh/known_hosts

or open it up and delete the entry for the offending ip/hostname

(P.S. It tells you exactly this in the error message you posted)

Its means your remote host key was changed (May be host password change),

Your terminal suggested to execute this command as root user

$ ssh-keygen -f "/root/.ssh/known_hosts" -R [www.website.net]:4231

You have to remove that host name from hosts list on your pc/server. Copy that suggested command and execute as a root user.

$ sudo su                                                            // Login as a root user

$ ssh-keygen -f "/root/.ssh/known_hosts" -R [www.website.net]:4231   // Terminal suggested command execute here
Host [www.website.net]:4231 found: line 16 type ECDSA
/root/.ssh/known_hosts updated.
Original contents retained as /root/.ssh/known_hosts.old

$ exit                                                               // Exist from root user

$ sudo ssh [email protected] -p 4231                              // Try again

I Hope this works.

Task Passwordless authentication for suer.

Error : Host key verification failed.

Source :10.13.1.11 Target : 10.13.1.35

Temporary workaround :

[user@server~]$ ssh [email protected] The authenticity of host '10.13.1.35 (10.13.1.35)' can't be established. RSA key fingerprint is b8:ba:30:46:a9:ab:70:12:1a:f2:f1:61:69:73:0a:19. Are you sure you want to continue connecting (yes/no)? yes Warning: Permanently added '10.13.1.35' (RSA) to the list of known hosts.

Try to authenticate user again...it will work.

Step1:$Bhargava.ssh#

ssh-keygen -R 199.95.30.220

step2:$Bhargava.ssh #

ssh-copy-id [email protected]

          Enter the the password.........

step3: Bhargava .ssh #

ssh [email protected]

Welcome to Ubuntu 14.04.3 LTS (GNU/Linux 3.13.0-68-generic x86_64) * Documentation: https://help.ubuntu.com/ Ubuntu 14.04.3 LTS server : 228839 ip : 199.95.30.220 hostname : qt.example.com System information as of Thu Mar 24 02:13:43 EDT 2016 System load: 0.67 Processes: 321 Usage of /home: 5.1% of 497.80GB Users logged in: 0 Memory usage: 53% IP address for eth0: 199.95.30.220 Swap usage: 16% IP address for docker0: 172.17.0.1 Graph this data and manage this system at: https://landscape.canonical.com/ Last login: Wed Mar 23 02:07:29 2016 from 103.200.41.50

hostname@qt:~$

Also sometimes there is situation when you are working on serial console, then checking above command in verbose mode -v will show you /dev/tty does not exists, while it does.

In above case just remove /dev/tty and create a symlink of /dev/ttyS0 to /dev/tty.

When you try to connect your remote server with ssh:

$ ssh username@ip_address

then the error raise, to solve it:

$ ssh-keygen -f "/home/local_username/.ssh/known_hosts" -R "ip_address"

This issue arises when the host key is expired or changed. you can remove the keys that host is using and try to ssh again, so that you are adding new key that is known to both client and server.

You can check the keys associated with your hosts with cat /.ssh/known_hosts . Now, You can remove the hosts keys manually or using the ssh-keygen option. You can do either of the following option.

1. Manual removal of keys

   vim /.ssh/known_hosts

delete the key that is associated with your host.

2. Remove key using ssh-keygen

   ssh-keygen -R your_host_or_host_ip

This will remove your key associated with the host.

Now, you can ssh to your host as usual and you will be asked if you want to continue to this host. Once your enter yes, this host will be added to your/.ssh/known_hosts with updated key. By now, you should be your host.

If you're sure the server is correct, sed -i 1d ~/.ssh/known_hosts will delete line 1 of your local ~/.ssh/known_hosts. The new correct key will be added to the file the next time you connect.

First you should remove existing key. SSH keys in most of Linux-based OS will be saved this file "/root/.ssh/known_hosts", so in order to remove the key related to host the following command will be used:

ssh-keygen -f "/root/.ssh/known_hosts" -R [Hostname]

Regards K1