Linux Command Line – Utility to Resolve Host Names Using /etc/hosts First

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There are several command line utilities to resolve host names (host, dig, nslookup), however they all use nameservers exclusively, while applications in general look in /etc/hosts first (using gethostbyname I believe).

Is there a command line utility to resolve host names that behaves like a usual application, thus looking in /etc/hosts first and only then asking a nameserver?

(I am aware that it would probably be like 3 lines of c, but I need it inside of a somewhat portable shell script.)

Best Answer

This is easily achieved with getent:

getent hosts 127.0.0.1

getent will do lookups for any type of data configured in nsswitch.conf.

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Reverse DNS – What is the Reverse DNS Command Line Utility?

The commands dig and host should be what you're looking for ;)

On *nix systems, you can use this command:

dig -x [address]

Alternatively, you can add +short at the end of the dig command to output only the DNS result.

There's also nslookup on both *nix and Windows systems for reverse DNS requests.

Nslookup Failure

QUERY What could be going wrong here?

A couple of things are conspiring against you. :-(

The file /etc/resolv.conf could be a problem; its domain line gets set to an inappropriate value when I reboot.

How is your /etc/resolv.conf being created/populated?

My guess is that your IP address is being assigned by a DHCP server. As part of the IP address assignment, your DHCP client is rewriting /etc/resolv.conf with the domain and nameserver assigned by the DHCP server. Hence, the "inappropriate" value after you reboot.

NSLOOKUP OUTPUT nslookup gives the SERVER address of the default name server, but says "can't find workshop: NX domain."

This is because your default DNS server is not your local DNS server -- it is one of the DNS servers assigned to you by the DHCP server. This "other" DNS server does not know about your domain.

But nslookup still doesn't work after I edit the line to "domain example.net" and restart bind9.

That's because you need to add your local DNS server to the list of nameservers in /etc/resolv.conf. Immediately before any other nameserver entry, add ...

nameserver 127.0.0.1

Now, when you use nslookup, your local DNS server should be your default DNS server. nslookup should now be able to resolve "workshop".

UPDATE Here is the output of dig: Command: dig A @workshop workshop.example.net

This confirms that you have your domain correctly configured on your local bind DNS server.

As you've already experienced, your changes to /etc/resolv.conf will be overwritten the next time you reboot. You have two options:

Reconfigure your machine to use a static IP. /etc/resolv.conf won't be overwritten anymore, so your changes will persist after a reboot.
Reconfigure your DHCP client so that it does not overwrite /etc/resolv.conf. This thread should point you in the right direction.

Best Answer

Related Solutions

Reverse DNS – What is the Reverse DNS Command Line Utility?

Nslookup Failure

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