Cfrgtkky

If you are running in certain remote/scripting situations where you lack interactive access to the prompt-to-add-hostkey, work around it like this:

$ ssh -o StrictHostKeyChecking=no user@something.example.com uptime

Warning: Permanently added 'something.example.com,10.11.12.13' (RSA) to the list of known hosts.

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 exist, while it does.

ssh -v user@hostname

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

rm /dev/tty

ln -s /dev/ttyS0 /dev/tty

As an alternative, add id_rsa.pub to the remote location, so password is not prompted and you get login access.

In my case, this was caused by a udev problem - there was no /dev/tty device node. The solution for me was just:

sudo mknod -m 666 /dev/tty c 5 0

On terminal:

ssh -o StrictHostKeyChecking=No -i YourPublicKey.pem user@example.com uptime

The following message, or similar, will appear:

Warning: Permanently added 'example.com, XX.XXX.XXX.XX' (ECDSA) to the list of known hosts.

 00:47:37 up 3 min,  0 users,  load average: 0.00, 0.00, 0.00

Then, connect to your EC2 as normal:

ssh -i YourPublickey.pem user@example.com

Well, it simply because the second ubuntu requires connection by key and not password.

I suggest you use sudo dpkg-reconfigure openssh-server on your pc, and then it should work properly. It will reset the configuration for openssh and should come back to a default password authentication.

Second possibility is that there's already a key for your other ubuntu in you PC, and that it changed thus being not recognized anymore. In this case, you'll have to edit the file .ssh/authorized_keys to remove the problematic line identifying your ubuntu.

This is an old thread and I just ran across this answer, I will just add what I did to solve this.

ssh-keygen -f "/home/USER/.ssh/known_hosts" -R HOSTNAME

I just looked at the error message that it threw at me and it said to run that command in order to remove it from the list of hosts. After that I did the following:

ssh-copy-id HOSTNAME

Than I followed the prompts from there until I was able to ssh into the server.

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 root@www.website.net -p 4231                              // Try again

Hope this works.

You should change your key in this way:
From your given error find which host-key changed for
example: Offending ECDSA key in /Users/user-name/.ssh/known_hosts:5
said 5th key changed, so do this:

sed -i '5d' ~/.ssh/known_hosts

Notice: you must be root or have privilege for sudo.

you have to put the rsa key of the target host into the source host /home/user/.ssh/known_hosts by running this on the target

ssh-keyscan -t rsa @targethost

May you just need to enter "yes" when ssh confirm you want to continue connectting.

Like bellow.

The authenticity of host 'xxx' can't be established.

ECDSA key fingerprint is yyy.

Are you sure you want to continue connecting (yes/no)? yes

Warning: Permanently added 'xxx' (ECDSA) to the list of known hosts.

Enter passphrase for key '/Users/ysy/.ssh/id_rsa':

Then enter your password.

Please pay attention to "Are you sure you want to continue connecting (yes/no)? yes". You must enter yes, not enter.

pico ~/.ssh/known_hosts and delete all lines, after just reconnect and you will get a new key.

My solution comes from this blog post: Algorithm negotiation failed for SSH Secure Shell Client

You need to modify the file as follows:

sudo nano /etc/ssh/sshd_config

And then add the following:

# Ciphers

Ciphers aes128-cbc,aes192-cbc,aes256-cbc,blowfish-cbc,arcfour

KexAlgorithms diffie-hellman-group1-sha1

Basically you tried different solutions until you find one which can solve your problem. If the above solutions don't work, please try this one. If this one doesn't work as well, please try others.

Just disable strict host key checking in your ~/.ssh/config:

Host *

StrictHostKeyChecking no

chmod 666 /dev/tty 

is yet another tty solution - sometimes, this device file has wrong permissions.