Tutorial :Getting the Hostname or IP in Ruby on Rails


I'm in the process of maintaining a Ruby on Rails app and am looking for an easy way to find the hostname or IP address of the box I'm on (since it's a VM and new instances may have different hostnames or IP addresses). Is there a quick and easy way to do this in Ruby on Rails?

Edit: The answer below is correct but the clarification Craig provided is useful (see also provided link in answer):

The [below] code does NOT make a connection or send any packets (to which is google). Since UDP is a stateless protocol connect() merely makes a system call which figures out how to route the packets based on the address and what interface (and therefore IP address) it should bind to. addr() returns an array containing the family (AF_INET), local port, and local address (which is what we want) of the socket.


From coderrr.wordpress.com:

require 'socket'    def local_ip    orig, Socket.do_not_reverse_lookup = Socket.do_not_reverse_lookup, true  # turn off reverse DNS resolution temporarily      UDPSocket.open do |s|      s.connect '', 1      s.addr.last    end  ensure    Socket.do_not_reverse_lookup = orig  end    # irb:0> local_ip  # => ""  



A simple way to just get the hostname in Ruby is:

require 'socket'  hostname = Socket.gethostname  

The catch is that this relies on the host knowing its own name because it uses either the gethostname or uname system call, so it will not work for the original problem.

Functionally this is identical to the hostname answer, without invoking an external program. The hostname may or may not be fully qualified, depending on the machine's configuration.

IP Address

Since ruby 1.9, you can also use the Socket library to get a list of local addresses. ip_address_list returns an array of AddrInfo objects. How you choose from it will depend on what you want to do and how many interfaces you have, but here's an example which simply selects the first non-loopback IPV4 IP address as a string:

require 'socket'  ip_address = Socket.ip_address_list.find { |ai| ai.ipv4? && !ai.ipv4_loopback? }.ip_address  


Try this:

host = `hostname`.strip # Get the hostname from the shell and removing trailing \n  puts host               # Output the hostname  


A server typically has more than one interface, at least one private and one public.

Since all the answers here deal with this simple scenario, a cleaner way is to ask Socket for the current ip_address_list() as in:

require 'socket'    def my_first_private_ipv4    Socket.ip_address_list.detect{|intf| intf.ipv4_private?}  end    def my_first_public_ipv4    Socket.ip_address_list.detect{|intf| intf.ipv4? and !intf.ipv4_loopback? and !intf.ipv4_multicast? and !intf.ipv4_private?}  end  

Both return an Addrinfo object, so if you need a string you can use the ip_address() method, as in:

ip= my_first_public_ipv4.ip_address unless my_first_public_ipv4.nil?  

You can easily work out the more suitable solution to your case changing the Addrinfo methods used to filter the required interface address.


This IP address used here is Google's, but you can use any accessible IP.

require "socket"  local_ip = UDPSocket.open {|s| s.connect("", 1); s.addr.last}  


Simplest is host_with_port in controller.rb

host_port= request.host_with_port  


The accepted answer works but you have to create a socket for every request and it does not work if the server is on a local network and/or not connected to the internet. The below, I believe will always work since it is parsing the request header.



Put the highlighted part in backticks:

`dig #{request.host} +short`.strip # dig gives a newline at the end  

Or just request.host if you don't care whether it's an IP or not.


Similar to the answer using hostname, using the external uname command on UNIX/LINUX:

hostname = `uname -n`.chomp.sub(/\..*/,'')  # stripping off "\n" and the network name if present  

for the IP addresses in use (your machine could have multiple network interfaces), you could use something like this:

 # on a Mac:   ip_addresses = `ifconfig | grep 'inet ' | grep -v | cut -d' ' -f 2`.split   => ['','']     # on Linux:   ip_addresses = `ifconfig -a | grep 'inet ' | grep -v | cut -d':' -f 2 | cut -d' ' -f 1`.split   => ['','']  


You will likely find yourself having multiple IP addresses on each machine (,, etc). If you are using *NIX as your OS, I'd suggest using hostname, and then running a DNS look up on that. You should be able to use /etc/hosts to define the local hostname to resolve to the IP address for that machine. There is similar functionality on Windows, but I haven't used it since Windows 95 was the bleeding edge.

The other option would be to hit a lookup service like WhatIsMyIp.com. These guys will kick back your real-world IP address to you. This is also something that you can easily setup with a Perl script on a local server if you prefer. I believe 3 lines or so of code to output the remote IP from %ENV should cover you.


io = IO.popen('hostname')  hostname = io.readlines    io = IO.popen('ifconfig')  ifconfig = io.readlines  ip = ifconfig[11].scan(/\ \d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\ /)  

The couple of answers with require 'socket' look good. The ones with request.blah_blah_blah assume that you are using Rails.

IO should be available all the time. The only problem with this script would be that if ifconfig is output in a different manor on your systems, then you would get different results for the IP. The hostname look up should be solid as Sears.


try: Request.remote_ip


Determine originating IP address. REMOTE_ADDR is the standard but will fail if the user is behind a proxy. HTTP_CLIENT_IP and/or HTTP_X_FORWARDED_FOR are set by proxies so check for these if REMOTE_ADDR is a proxy. HTTP_X_FORWARDED_FOR may be a comma- delimited list in the case of multiple chained proxies; the last address which is not trusted is the originating IP.

Update: Oops, sorry I misread the documentation.

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