Ubuntu – local DNS lookup not working, despite everything is in /etc/hosts


I am running Ubuntu (12.04) on Virtual Box and want my machine to be able to lookup its own hostname, the same way other VMs will do in this network (I am trying to build virtual cluster). There is no DNS server, IP are assigned by VirtualBox, and I just map them in /etc/hosts.

The machine name is node1 and I have /etc/hosts like that:

user@node1-VirtualBox:~$ cat /etc/hosts   localhost  node1-VirtualBox.cs.ucl.ac.uk node1-VirtualBox
#  node1-VirtualBox

# 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

So I would assume that

  1. Fully qualified hostname would be node1-VirtualBox.cs.ucl.ac.uk
  2. node1 and node1-VirtualBox.cs.ucl.ac.uk would resolve to (and vice versa)

From hostname I am getting this:

$hostname ->  node1-VirtualBox   (OK)

$hostname --fqdn -> node1-VirtualBox.cs.ucl.ac.uk (OK)

$hostname --A -> node1.local node1.cs.ucl.ac.uk (OK i guess)

hostname looks promising, but when I try to get IP addresses using host, it doesn't work…

user@node1-VirtualBox:~$ host -v -t A node1-VirtualBox
Trying "node1-VirtualBox.cs.ucl.ac.uk"
Trying "node1-VirtualBox"
Host node1-VirtualBox not found: 3(NXDOMAIN)
Received 110 bytes from in 1 ms

user@node1-VirtualBox:~$ host -v -t A
Trying ""
Host not found: 3(NXDOMAIN)
Received 108 bytes from in 2 ms

Any idea why this isn't working? From what I read and see in config, if DNS is done on localhost, it should just check /etc/hosts… and everything is there, right? And SSH is working, so clearly this file is correct?

Below my configuration:

# /etc/nsswitch.conf
# Example configuration of GNU Name Service Switch functionality.
# If you have the `glibc-doc-reference' and `info' packages installed, try:
# `info libc "Name Service Switch"' for information about this file.

passwd:         compat group:          compat shadow:         compat

hosts:          files mdns4_minimal [NOTFOUND=return] dns mdns4 networks:       files

protocols:      db files services:       db files ethers:         db files rpc:            db files

netgroup:       nis

# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
search cs.ucl.ac.uk

eth0      Link encap:Ethernet  HWaddr 08:00:27:da:a1:bc  
          inet addr:  Bcast:  Mask:
          inet6 addr: fe80::a00:27ff:feda:a1bc/64 Scope:Link
          RX packets:169 errors:0 dropped:0 overruns:0 frame:0
          TX packets:176 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:123968 (123.9 KB)  TX bytes:21551 (21.5 KB)

eth1      Link encap:Ethernet  HWaddr 08:00:27:99:65:51  
          inet addr:  Bcast:  Mask:
          inet6 addr: fe80::a00:27ff:fe99:6551/64 Scope:Link
          RX packets:268 errors:0 dropped:0 overruns:0 frame:0
          TX packets:252 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:78333 (78.3 KB)  TX bytes:71866 (71.8 KB)

lo        Link encap:Local Loopback  
          inet addr:  Mask:
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:12527 errors:0 dropped:0 overruns:0 frame:0
          TX packets:12527 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:23857104 (23.8 MB)  TX bytes:23857104 (23.8 MB)


Ok, it turns out the "host" command not resolving was a bit of red herring for my original problem – it couldn't work because it doesn't look into /etc/hosts, as explained in answers below.

The original issue was lack of canonical hostname i.e. hostname --fqdn was returning localhost. To fix it i had to have this: node1-VirtualBox.cs.ucl.ac.uk node1-VirtualBox as second line in my /etc/hosts.

However for making it actually work i had to restart my machines and reinstall Cloudera on my cluster.

Best Answer

You are doing everything right like putting the entries in /etc/hosts, server address in /etc/resolv.conf, the /etc/nsswitch.conf looks good too.

The problem you are having is due to the understanding of a very specific term "nameserver". All the commands used to resolve IP address to hostname and vice versa used the nameserver addresses from /etc/resolv.conf unless mentioned explicitly. You have put nameserver which is not a valid name server because it is not configured as a nameserver. It is there because of dnsmasq which acts as a DNS cacher (and DHCP server) but host, dig, nslookup take data from a valid, configured nameserver only.

As the host, nslookup, dig commands will use the "nameserver" mentioned in /etc/resolv.conf (unless specified), hostname resolution will not work using these in your case. Although the programs that use /etc/nsswitch.conf or read /etc/hosts will resolve the hostname to IP addresses and vice versa.

If you want to resolve hostnames from /etc/hosts the you need to use getent. For example to resolve "node1-VirtualBox", you need the following command :

getent hosts node1-VirtualBox