How Do You Troubleshoot the Error “curl: (6) Could not resolve host: Unknown error”?

Problem scenario
You are using RedHat Enterprise Linux in AWS.  curl commands are not working.  DNS names are not resolving accurately.  For example, you try this command:  curl

You get this error:
"curl: (6) Could not resolve host:; Unknown error"
How do you fix this to get curl commands to work (and make sure that FQDNs resolve properly)?

Do these four things:

1.  sudo cp /etc/modprobe.d/disableipv6.conf /etc/modprobe.d/bak.disableipv6.conf.bak
2.  sudo su -
3.  echo "install ipv6 /bin/true" >> /etc/modprobe.d/disableipv6.conf
4.  Reboot the server.

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    1. If this did not work, was there an error message? If there was no error message, what step did you get to when there was a problem?

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