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How to troubleshoot DNS-related issues

Environment

Product Version
Pivotal Greenplum (GPDB) 4.3.x
OS RHEL 6.x

Purpose

Sometimes the customer may report being unable to ping certain hostnames but pinging the IP address works. Then it is an issue to resolve the hostname.

Procedure

Here are a couple of items we can check to find the root cause of each hostname resolving issue:

Follow the steps to resolve this issue:

  1. Check the content of /etc/nsswitch.conf file, as this conf file will tell Linux which name-resolving method to use.
  2. Check /etc/hosts file. This file will help Linux directly resolve hostnames if this method is listed in the nsswitch.conf file.
  3. Check /etc/resolv.conf file. This file will tell if this host set up any DNS service yet.
  4. Check dnsmasq and nscd service. These two services can be used for the DNS cache. Sometimes the customer may ask why the hostname resolving is still working while /etc/hosts  has no entry and the DNS service has stopped. The reason is that DNS cache service is still running.

Additional Information

Here are a few useful resources to know more about those Linux services:

http://searchitchannel.techtarget.com/feature/Using-nsswitchconf-to-find-Linux-system-information

http://linux.die.net/man/8/dnsmasq

https://en.wikipedia.org/wiki/Dnsmasq
http://linux.die.net/man/8/nscd

 

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