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Localhost vs.

asked 2018-07-17 11:07:52 -0500

pitosalas gravatar image

updated 2018-07-22 19:01:29 -0500

I've had problems troubleshooting IP addresses with my setup and want to verify some questions, if you could help:

  1. Should I use localhost or when referring to myself, or does it have to be a real URI?

  2. I have read that if you don't have a DNS name, you must use ROS_IP and not ROS_HOSTNAME, yet I see many examples where an ip address is used for ROS_HOSTNAME. For example, here: near the end you will see ROS_HOSTNAME=

  3. Can I omit both ROS_IP and ROS_HOSTNAME usually - unless I have more than one network adapter. If I have more than one then by default ROS would use all of them. But by specifying ROS_IP or ROS_HOSTNAME I can limit ROS to a specific one.


  1. On the computer running ROSCORE, I understand that this is almost always sufficient.

export ROS_MASTER_URI=http://localhost:11311

Under what special circumstances does that computer need a specific IP address of ROS_MASTER? And does it ever need ROS_IP or ROS_HOSTNAME?


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Do you have links for these examples?

jayess gravatar image jayess  ( 2018-07-17 11:15:29 -0500 )edit

You can use either ROS_IP or ROS_HOSTNAME. If you have both set, ROS_HOSTNAME will take precedence. See

jayess gravatar image jayess  ( 2018-07-17 11:18:16 -0500 )edit

Here's one example specifying an IP address with ROS_HOSTNAME: (you have to look for it near the end of that page.)

Also what about localhost vs.

pitosalas gravatar image pitosalas  ( 2018-07-17 16:24:19 -0500 )edit

That tutorial that you linked to is incorrect. ROS_HOSTNAME is for hostnames such as localhost, not IP addresses as that's what ROS_IP is for.

jayess gravatar image jayess  ( 2018-07-17 16:47:43 -0500 )edit

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answered 2018-07-17 16:53:26 -0500

jayess gravatar image

updated 2018-07-17 16:55:18 -0500

I'll answer your question to best of my ability.

  • is the loopback address (also known as localhost).
  • is a non-routable meta-address used to designate an invalid, unknown or non applicable target (a no particular address placeholder).

As for the bottom line, it's a matter of preference as to which to use. I prefer ROS_HOSTNAME because I can use it in launch files in the <machine> tag and it's easier to remember hostnames vs. IP addresses.

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Thanks! Please check the followup question in the original post under "followup"? Thanks!!!

pitosalas gravatar image pitosalas  ( 2018-07-22 19:01:08 -0500 )edit

I'll take a look at it if you post it as a new question. You can provide a link back to this question keep the continuity

jayess gravatar image jayess  ( 2018-07-22 19:03:12 -0500 )edit

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Asked: 2018-07-17 11:07:52 -0500

Seen: 1,524 times

Last updated: Jul 22 '18