"Unknown host" means you tried to ping to a hostname that could not be resolved to an IP-Address by your domain name server (or the /etc/hosts file of your Ubuntu machine). This has nothing to do with the ssh file.
Look here viewtopic.php?f=91&t=206115#p1276886
if you are trying to do a headless setup.
If you write the image by Ubuntu you can additionally configure a static IP address for your Raspberry Pi before you boot it from the SD card. Edit the /etc/dhcpcd.conf file on the (ext4) root partition of the SD card. There are examples in the comments. Ask again if you are unsure, how to do it.