name resolution puzzle

[Philipp Vlassakakis]

Hi,

As far as I know, neither „nslookup“, nor "host" uses /etc/hosts, regardless if you add „files dns“ to /etc/nsswitch.conf
You can check the entries via "ping".

See truss:

host google.de <http://google.de/>
[…]
open("/etc/resolv.conf",O_RDONLY,0666)		 = 3 (0x3)

dig google.de <http://google.de/>
[…]
open("/etc/resolv.conf",O_RDONLY,0666)		 = 3 (0x3)

Regards,
Philipp

> Am 03.08.2018 um 23:41 schrieb Valeri Galtsev <galtsev at kicp.uchicago.edu>:
> 
> Dear Experts,
> 
> I just noticed some behavior of commands "host" and "nslookup" that puzzles me. Namely, they do not query /etc/hosts file first, but query nameserver instead, even though nsswitch.conf order is "files dns":
> 
> $cat /etc/nsswitch.conf | grep hosts
> 
> hosts: files dns
> 
> $ cat /etc/hosts | grep holometer.uchicago.edu
> 
> 128.135.20.84	holometer holometer.uchicago.edu
> 
> $ host holometer.uchicago.edu
> 
> holometer.uchicago.edu has address 128.135.52.70
> 
> $ nslookup holometer.uchicago.edu
> 
> Server:		128.135.249.50
> Address:	128.135.249.50#53
> 
> Name:	holometer.uchicago.edu
> Address: 128.135.52.70
> 
> 
> So, it appears, that the commands "host" and "nslookup" go directly to DNS server, and do not look into /etc/hosts first which I have expected.
> 
> I should mention that other compiled programs do obey the nsswitch.conf query order.
> 
> 
> Can someone enlighten me on this?
> 
> 
> The reason I have different IP in /etc/hosts is: I'm building the box to migrate some host to, and I'd like to test some stuff that should work from other machines before I switch DNS records to new IP. So, on these external machines I am trying to have hostname resolve into future IP just by adding it to /etc/hosts.
> 
> Thanks.
> Valeri
> 
> -- 
> ++++++++++++++++++++++++++++++++++++++++
> Valeri Galtsev
> Sr System Administrator
> Department of Astronomy and Astrophysics
> Kavli Institute for Cosmological Physics
> University of Chicago
> Phone: 773-702-4247
> ++++++++++++++++++++++++++++++++++++++++
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