I got error "hostname: Name or service not known" when checking IP of hostname

Question

I'm running Ubuntu 14.04 on my company's cloud service (my instance has elastic IP).  I want to check out the IP address of my instance I'm running by command line, but it didn't work.

root@ubuntu14-graphite:~# hostname
ubuntu14-graphite
root@ubuntu14-graphite:~# hostname -i
hostname: Name or service not known

I don't understand the reason why. 

I tried to ping to ubuntu14-graphite but it said:

unknown host ubuntu14-graphite.

Does that mean my host doesn't even exist?

I have another server (not cloud instance but physical server).  In this server I installed CentOS 6.7.  I checked the hostname's IP and it worked even though there was nothing special in /etc/hosts.

Here's the output of cat /etc/hosts:

127.0.0.1   localhost

# 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

Answer 1

It means that "the system" (I'm using that term in a broad, general, ambiguous sense) doesn't know that the name ubuntu14-graphite corresponds to your host and its IP address.  (The fact that is is your host's name isn't enough to make this happen.)  This almost surely means that you don't have a line for ubuntu14-graphite in your /etc/hosts file^†, and that it's not in your naming service (e.g., DNS or NIS).  Consequently, a way to fix it is to add ubuntu14-graphite (and its IP address) to your /etc/hosts.  If you're using a more sophisticated (distributed) naming system such as DNS or NIS (or maybe ActiveDirectory?), the ultimate solution is to add your host to that service.
_____________
† ... and I see from your post of your hosts file that this is the case.

There is some debate over the question of what IP address you should associate with your host name.  Everyone agrees that it should be an address that "works" for your host; i.e., commands like ping A.B.C.D should succeed.  Some people recommend using a loopback address.  Loopback addresses are always of the form 127.B.C.D; common values are 127.0.0.1 and 127.0.1.1.  Other people recommend using a LAN address, which might look like 192.168.C.D (but it can be almost anything) — but you should not put a dynamically assigned address into your hosts file (and, if you're using DHCP with DNS, then the dynamically assigned address(es) should be entered into your DNS records automatically).  Use commands like ifconfig and hostname -I to see what addresses are in use.

Answer 2

The actual way to check a machine's IP address is by using the ifconfig command.

Note that depending on the actual cloud setup, the server instance may not be aware of the public IP and only know a VLAN IP. For details on this, you need to refer to your provider's documentation.

Answer 3

Add the myhostname entry to the hosts service in /etc/nsswitch.conf.

In other words, change this line in /etc/nsswitch.conf:

hosts:      files dns

to this:

hosts:      files dns myhostname

Where usually hostnames are resolved using the /etc/hosts file and dns, the hostname of the system can also be resolved by telling the Name Service Switch to do so (as this configuration change will do).

This would explain why you didn't see anything special about the /etc/hosts file on the system that you could resolve the local hostname.

More information on the myhostname flag is here.

Answer 4

In my opinion it depends on version of hostname command (net-tools package).

See: https://bugzilla.redhat.com/show_bug.cgi?id=319981

• example on "openSuse Leap 42.3":

    # hostname -V
    net-tools 1.60
    hostname 1.100 (2001-04-14)

    # hostname -i
    hostname: Name or service not known

• on Lubuntu 17.10

  $ hostname -V
  hostname 3.18

hostname -i - gives me information about IPv6 and IPv4

Answer 5

Go to etc/hosts.save check your hostname there. And then edit /etc/hosts to write there your hostname and the hostname in hosts.save. Also check the IP address. Example:

127.0.0.1    ubuntu   
127.0.1.1    ubuntu.ubuntu-domain    ubuntu