Host Command – Why Does the Host Command Not Resolve Entries in /etc/hosts?

domain-name-systemlinuxUbuntu

I have the following /etc/hosts file on a ubuntu 12.04 machine

127.0.0.1 localhost
10.248.27.66 ec2-50-112-220-110.us-west-2.compute.amazonaws.com puppetmaster

# The following lines are desirable for IPv6 capable hosts
::1 ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts

However the host command does not resolve the name puppetmaster correctly, while the telnet command is does

root@ip-10-248-34-162:/home/ubuntu# host puppetmaster
Host puppetmaster not found: 3(NXDOMAIN)

root@ip-10-248-34-162:/home/ubuntu# telnet puppetmaster 8140
Trying 10.248.27.66...
Connected to ec2-50-112-220-110.us-west-2.compute.amazonaws.com.
Escape character is '^]'.

Why does the host command not resolve entries in /etc/hosts?

Best Answer

The host program uses libresolv to perform a DNS query directly, i.e., does not use gethostbyname.

Most programs, when attempting to connect to another host, invoke the gethostbyname system call or a similar function. This function obeys the configuration of /etc/nsswitch.conf. This file has a line which in Ubuntu 12.04 defaults to the following:

hosts:          files mdns4_minimal [NOTFOUND=return] dns mdns4

which means that it will first use /etc/hosts, then fall back to DNS queries.

If you want to perform a host lookup this way, you can do this with getent hosts. For example:

$ getent hosts serverfault.com
198.252.206.16  serverfault.com

I hope this helps.

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