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
127.0.0.1 localhost
192.168.56.103 node1-VirtualBox.cs.ucl.ac.uk node1-VirtualBox
#10.0.2.15 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
- Fully qualified hostname would be node1-VirtualBox.cs.ucl.ac.uk
- node1 and node1-VirtualBox.cs.ucl.ac.uk would resolve to 192.168.56.103 (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 127.0.0.1#53 in 1 ms
user@node1-VirtualBox:~$ host -v -t A 192.168.56.103
Trying "103.56.168.192.in-addr.arpa"
Host 103.56.168.192.in-addr.arpa. not found: 3(NXDOMAIN)
Received 108 bytes from 127.0.0.1#53 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
resolv.conf:
# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
# DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
nameserver 127.0.0.1
search cs.ucl.ac.uk
ifconfig:
eth0 Link encap:Ethernet HWaddr 08:00:27:da:a1:bc
inet addr:10.0.2.15 Bcast:10.0.2.255 Mask:255.255.255.0
inet6 addr: fe80::a00:27ff:feda:a1bc/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
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:192.168.56.103 Bcast:192.168.255.255 Mask:255.255.0.0
inet6 addr: fe80::a00:27ff:fe99:6551/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
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:127.0.0.1 Mask:255.0.0.0
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)
POST MORTEM:
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:
192.168.56.103 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 putnameserver 127.0.0.1
which is not a valid name server because it is not configured as a nameserver. It is there because ofdnsmasq
which acts as a DNS cacher (and DHCP server) buthost
,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 usegetent
. For example to resolve "node1-VirtualBox", you need the following command :