How to establish ssh key pair when "Host key verification failed"

Question

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.

Answer 1

ssh-keygen -R hostname 

This deletes the offending key from the known_hosts

The man page entry reads:

-R hostname Removes all keys belonging to hostname from a known_hosts file. This option is useful to delete hashed hosts (see the -H option above).

Answer 2

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