This error means that the hostname you are trying to connect to cannot be resolved to an IP address. ... If you have verified that the hostname is correct, there may be a problem with your DNS server (or with your ISP's DNS server, if you are a standalone user). It may be unable to resolve hostnames to IP addresses.

How do I fix unable to resolve host?

To fix this error, edit the /etc/hosts file and set the hostname (newpc) with a loopback address (127.0. 0.1). As you can see the error “sudo: unable to resolve host” disappeared. Note : If the old hostname is present in the /etc/hosts file then just replace them with the new hostname.

Why does IP address not resolve to a hostname?

Why? usually it means that the DNS your computer communicates with does not have PTR record indicating a hostname for the IPv4 address or the DNS did not respond (not operational or wrong IP) or the left control panel checkbox 'Resolve IPs to Hostnames' is unchecked.