The Domain can not be resolved to it's IP address.
If you have your DNS running local, try restarting it. If not, check your DNS or add a different server to /etc/resolve.conf (i.e. nameserver 8.8.8.8).
You can also add the domain as a static entry in your hosts file:
On your linux server add the DNS information to your /etc/hosts file using:
echo '127.0.0.1 www.otherdomain.com' >> /etc/hosts
…where 127.0.0.1 is the IP address of your website and www.otherdomain.com the domain name your using.
You can find the IP address of any domain using nslookup, i.e
nslookup www.otherdomain.com
but you can run 'host url' in a shell window
mean? Like runningping <site url>
from that site's server? – Treble