Ubuntu Sudo appears unable to resolve host solution

Ubuntu Sudo appears unable to resolve host solution
Ubuntu environment, assuming that this machine name is ABC (machine's hostname), each execution sudo will appear this warning message:
Sudo:unable to resolve host ABC
Although sudo can still be performed normally, it is set directly from/etc/hosts, so that ABC (hostname) can be returned to the 127.0.0.1 IP.

Add the host name (hostname) after 127.0.0.1 localhost:

127.0.0.1 localhost ABC

Ubuntu Sudo appears unable to resolve host solution