Re: BASH ssh problem - changing SD card OS in Rpi causes this - HELP !
If by Rpi you mean a Raspberry Pi (or any computer with sshd) the files you want to replicate on your own computers are the "key" files is /etc/ssh. Otherwise those files are uniquely generated the first time you run Raspbian.
You probably need to use sudo to cp those files into place, whether you do that directly to the SD card, or scp them over in your username and then use sudo cp to copy them into /etc/ssh.
On thing you may want to do is install avahi-browser on your Rpi's. Set a different hostname in /etc/hostname and /etc/hosts of each SD card and then you can access them from Ubunu (or Apple or Windows with Bonjour installed) with their hostname.local
efflandt@raspberrypi ~ $ ls /etc/ssh
moduli ssh_host_dsa_key ssh_host_ecdsa_key.pub
ssh_config ssh_host_dsa_key.pub ssh_host_rsa_key
sshd_config ssh_host_ecdsa_key ssh_host_rsa_key.pub
efflandt@XPS8100-1204:~$ tracepath -n raspberrypi.local
1: 172.16.0.50 0.104ms pmtu 1500
1: 172.16.0.102 46.849ms reached
1: 172.16.0.102 23.246ms reached
Resume: pmtu 1500 hops 1 back 64
i5 650 3.2 GHz, 8 GB, nvidia GTX 550 Ti @ 1080p (year old GT 430 began freezing) and assorted other computers