Linux – Copy the ssh key to remote machine via ssh-copy-id in a script without prompt

As Ethabell mentioned, you can copy over the current host keys to the new server.

You can find your host keys by opening your sshd_config file (On my Ubuntu 12.04 box its /etc/ssh/sshd_config). In the config file look for the HostKey entries. These entries will tell you where the host key files are located. You should be able to copy these files to the new server and update the new server's sshd_config to point to the copied keys (or just overwrite the files that already exist on the new server).

Also, note this section from the sshd_config man page, specifically the part about permissions:

Specifies a file containing a private host key used by SSH. The default is /etc/ssh/ssh_host_key for protocol version 1, and /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_ecdsa_key and /etc/ssh/ssh_host_rsa_key for protocol version 2. Note that sshd(8) will refuse to use a file if it is group/world-accessible. It is possible to have multiple host key files. “rsa1” keys are used for version 1 and “dsa”, “ecdsa” or “rsa” are used for version 2 of the SSH protocol.

ssh -i selects a file from which the identity (private key) or public key authentication is read.

You could configure ssh to use it in your config for this host so you do not have to specify it.

Add to ~/.ssh/config (replace server.example.com with hostname or IP of your server):

Host server.example.com
    User username
    Hostname server.example.com
    PreferredAuthentications publickey,password
    IdentityFile ~/.ssh/id_rsa.pub

This config will make your connection to always try to use id_rsa.pub key and then fallback to password if key would not be available for some reason.

So now you should be able to use ssh <user>@<host> <command> with it automatically using your private key for authentication.