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hagrawal
Asked: 2016-06-24 13:41:24 +0800 CST

How to get list of all the hostname / DNS of the Linux box

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I have a Linux box and I know I can get the list of IP addresses assigned to that box using following command /sbin/ifconfig -a but how to I get the list of hostnames / DNS for that Linux box using single command?

Why I asking this is because using /sbin/ifconfig -a I see that there are ~6 ethernets connected to it and in those 4 are active. Now, all those have different IP addresses, so I have 4 different IP addresses for my Linux box (please correct me if I am wrong here ??). Now, my Weblogic application server has defined listen address as, lets say abc.fb.us and xyz.fb.us etc. Now when I ping each hostname (should I call abc.fb.us as hostname or DNS or alias ??) then I get some IP address which is listed when I do ifconfig.

I know I can do nslookup 172.22.33.11 and I will get abc.fb.us, assuming that's the IP address of abc.fb.us.

But I want to get a list of hostnames using single command, much like the way I got list of IP address.

I have checked my /etc/hosts and it doesn't have abc.fb.us, xyz.fb.us etc. so clearly there is some other way these names are configured and how do I get all the hostnames?

linux ip-address hostname linux-networking

3 Answers

  1. You can't get this information at all, at least in a reliable and complete way. The system doesn't need to be aware of what DNS names for what domain are pointing to it.

    If PTR records are defined, you can get these like Brennen described, but everything else is unreliable.

    As an example, nothing prevents me from setting up DNS entries for any IP address and try to connect to the address using that DNS entry. For most protocols, you will be completely unaware that this has happened (HTTP is a major exception, as it will transfer the hostname in the HOST header).

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  2. You can't do what you want to do. There is no single command that will give you the information you want.

    Additionally, there can be multiple forward (A) records for a a single IP address as well as CNAME records all of which are hostnames for the system.

    You could try dumping your DNS config and searching for all records that have the same IP addrress, then search to see if any CNAME records refer to the A record names. This isn't simple and certainly isn't a single command.

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  3. Best Answer

    This one liner will work:

    ifconfig | grep 'inet addr:' | cut -d: -f2 | awk '{ print $1}' | xargs -L1 host

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