14.04.6 sudo: unable to resolve host [myHostName]

[noideas]

Ubuntu 14.04.6 LTS. Whenever I disable any form of internet access (wifi and/or wired), then every sudo I type generates:

sudo: unable to resolve hostname [myHostname]

Followed by not being able to ping localhost and myHostName. Raw IP addresses 127.0.0.1 and 127.0.1.1 are still pinged properly. HOSTS file has correct entries for localhost and myHostName - I've checked many, many times.

As soon as I enable Wifi/wired (and when it connects to the access point/network), I am able to ping localhost, which is correctly resolved to 127.0.0.1. BUT, pinging myHostName produces no response and resolves to some arbitrary IP (125.235.4.51)
Avahi-resolve outright refuses to resolve localhost, myHostName and anything on the local network. If avahi-autoipd is running, avahi resolves the local network's IPv6 hostnames (not IPv4), but ping command still cannot. Nslookup resolves the IPv4 but produces the same random ip (125.235.4.51) on nslookup myhostname.

Same results when doing all of the above from TTY.

What can be the reason?

[TheFu]

14.04 + 5 years = .....
support ended last year. please move to a supported release or contact canonical's paid support team.