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Configuring ROS In Your Shell Environment

If you already have your own ROS shell configuration, you can probably skip over the basic configuration.

🔔 If you prefer zsh over bash, replace most instances of .bash in this document with .zsh and write to ~/.zshrc instead of ~/.bashrc. You'll also want to change the last element of the args array in enter-container.sh from bash to zsh.

Basic Configuration

TL;DR

If your workflow runs entirely on a single computer, we recommend adding this set of lines to your ~/.bashrc

if [[ -f /opt/ros/noetic/setup.bash ]]; then
  source /opt/ros/noetic/setup.bash

  export ROS_MASTER_URI="http://localhost:11311"
  export ROS_IP="127.0.0.1"
fi

Explanation

As stated in the ROS installation instructions, you need to run this command in every shell environment in order to use ROS.

source /opt/ros/noetic/setup.bash

Doing this manually in every shell is very inconvenient, so they recommend adding the command to your ~/.bashrc file, which is run as part of each shell's initialization procedure. If you do this, ROS will work in the Docker container, but when you create a new shell on the host system you'll probably be greeted with an error:

bash: /opt/ros/noetic/setup.bash: No such file or directory

bash is telling you that the file /opt/ros/noetic/setup.bash does not exist on the host system. Note that this shouldn't cause any adverse effects on the host, but you might find this message annoying. We can handle the error by checking whether the file exists before trying to source it:

if [[ -f /opt/ros/noetic/setup.bash ]]; then
  source /opt/ros/noetic/setup.bash
fi

The if statement should evaluate to false on the host and true inside the Docker container.

Lastly, we'll set some environment variables so ROS can find resources on the network.

if [[ -f /opt/ros/noetic/setup.bash ]]; then
  source /opt/ros/noetic/setup.bash

  export ROS_MASTER_URI="http://localhost:11311"
  export ROS_IP="127.0.0.1"
fi

The code block above assumes that you're only using ROS on your local machine. You will need to modify the variables accordingly if you need multiple machines to communicate with one another over a network.

ROS_MASTER_URI specifies the address of the roscore server and, implicitly, the network interface ROS is using on the server. The ROS_MASTER_URI address should be reachable through every systems's ROS_IP address and corresponding network interface.

ROS_IP specifies the IP address for this system and, implicitly, the network interface that ROS should use to connect to the roscore server. If ROS_HOSTNAME is also set, ROS_HOSTNAME will take precedence over ROS_IP, but hostname resolution might not be available in all situations.

You can find the full list of ROS 1 environment variables here. Most of them do not need to be changed from their default values.

Advanced Configuration

If you are using ROS on multiple machines over a network and you are not able to configure static IP addresses, you may find that you often need to modify ROS_MASTER_URI and ROS_IP and re-source your shell rc file. This is particularly inconvenient when you already have multiple shells open and you have to re-source in all of them.

In this section we outline additional configuration that performs two tasks:

  1. Set the ROS_IP automatically to that of your computer's default gateway. 🔔 This does not set up ROS_MASTER_URI!
  2. Dynamically load changes to these environment variables so you don't have to manually type source .<shell>rc after making changes.

Automatically Set ROS_IP

To set ROS_IP automatically, start by creating a new file, e.g. ~/.rosrc and add these commands to the file:

### file: ~/.rosrc

ROS_GATEWAY=$(ip route list default | cut -d " " -f 5)

export ROS_IP=$(ip -4 -br addr show $ROS_GATEWAY | tr -ts "/" " " | cut -d " " -f 3)

export ROS_MASTER_URI=http://$ROS_IP:11311

These commands find the default gateway of your computer and its associated IP address while massaging the output into a format that we can use.

There are two caveats here:

  1. If you know you're using a non-default gateway, e.g., a USB network adapter or a VPN, you'll want to manually set ROS_GATEWAY to the name of that gateway.
  2. The code block above uses ROS_IP to set ROS_MASTER_URI. This is correct behavior for the machine that will be running roscore, but all other machines will need to have this set manually to the server's IP address (which may change if it's dynamic).

Automatically Re-source ~/.rosrc

We will use different features of bash and zsh to run commands automatically in their respective shell environments.

In bash, this feature is the PROMPT_COMMAND shell variable, which runs a command immediately before the shell prompt is drawn. Note that if the prompt is already drawn on the screen, PROMPT_COMMAND will not run until the next time the prompt is drawn, so you'll need to hit enter for it to run.

In zsh, this feature is the preexec function, which runs immediately before executing a shell command. The function does not run between chained commands; preexec effectively runs the function immediately after you hit enter.

Since these features inject commands into your shell environment behind-the-scenes, you'll want to keep the runtime of the commands as short as possible so you don't introduce too much latency in your shell. The contents of ~/.rosrc above typically run in a few milliseconds.

We can update the ROS block of your shell file as follows.

Bash:

### file: ~/.bashrc

if [[ -f /opt/ros/noetic/setup.bash ]]; then
  source /opt/ros/noetic/setup.bash

  PROMPT_COMMAND="source ~/.rosrc"
fi

Zsh:

### file: ~/.zshrc

if [[ -f /opt/ros/noetic/setup.zsh ]]; then
  source /opt/ros/noetic/setup.zsh

  preexec() {
    source ~/.rosrc
  }
fi

You can check the values of ROS environment variables in either shell using

env | grep ROS