Navigating the ROS Filesystem
This tutorial introduces ROS filesystem concepts, and covers using the roscd, rosls, and rospack commandline tools using Erle board through all the process.
Quick Overview of Filesystem Concepts
- Packages: Packages are the software organization unit of ROS code. Each package can contain libraries, executables, scripts, or other artifacts.
- Manifest (package.xml): A manifest is a description of a package. Its serves to define dependencies between packages and to capture meta information about the package like version, maintainer, license, etc...
Code is spread across many ROS packages. Navigating with command-line tools such as ls and cd can be very tedious which is why ROS provides tools to help you.
rospack allows you to get information about packages. In this tutorial, we are only going to cover the find option, which returns the path to package.
# rospack find [package_name]
If you get the following error:
rospack find roscpp terminate called after throwing an instance of 'std::runtime_error' what(): locale::facet::_S_create_c_locale name not valid Aborted
you can solve it setting the following environment variable:
root@erlerobot:~# rospack find roscpp /opt/ros/groovy/share/roscpp
roscd is part of the rosbash suite. It allows you to change directory (cd) directly to a package or a stack.
# roscd [locationname[/subdir]]
Run this example:
root@erlerobot:~# roscd roscpp root@erlerobot:/opt/ros/groovy/share/roscpp# pwd /opt/ros/groovy/share/roscpp
You can see that
/opt/ros/groovy/share/roscpp is the same path that rospack find gave in the previous example.
roscd, like other ROS tools, will only find ROS packages that are within the directories listed in your
ROS_PACKAGE_PATH environment variable. To see what is in your
root@erlerobot:~# echo $ROS_PACKAGE_PATH /root/catkin_ws/src:/opt/ros/groovy/share:/opt/ros/groovy/stacks
ROS_PACKAGE_PATH should contain a list of directories where you have ROS packages separated by colons.
Similarly to other environment paths, you can add additional directories to your
ROS_PACKAGE_PATH, with each path separated by a colon ':'.
roscd can also move to a subdirectory of a package or stack.
root@erlerobot:~# roscd roscpp/cmake root@erlerobot:/opt/ros/groovy/share/roscpp/cmake# pwd /opt/ros/groovy/share/roscpp/cmake
roscd log will take you to the folder where ROS stores log files. Note that if you have not run any ROS programs yet, this will yield an error saying that it does not yet exist.
root@erlerobot:~# roscd log No active roscore
If we launch
roscore and then run the same command in another window (or launch
roscore in background appending
& at the end):
root@erlerobot:~/.ros/log# roscore ... logging to /root/.ros/log/53689ab4-bfe7-11d3-af71-1e658b3e1294/roslaunch-erlerobot-1104.log Checking log directory for disk usage. This may take awhile. Press Ctrl-C to interrupt Done checking log file disk usage. Usage is <1GB. started roslaunch server http://erlerobot:55088/ ros_comm version 1.9.44 SUMMARY ======== PARAMETERS * /rosdistro * /rosversion NODES auto-starting new master process[master]: started with pid  ROS_MASTER_URI=http://erlerobot:11311/ setting /run_id to 53689ab4-bfe7-11d3-af71-1e658b3e1294 process[rosout-1]: started with pid  started core service [/rosout]
root@erlerobot:~# roscd log root@erlerobot:~/.ros/log/53689ab4-bfe7-11d3-af71-1e658b3e1294# ls master.log roslaunch-erlerobot-1104.log rosout-1-stdout.log rosout.log
`rosls is part of the rosbash suite. It allows you to ls directly in a package by name rather than by absolute path.
# rosls [locationname[/subdir]]
root@erlerobot:~/catkin_ws/devel# rosls catkin cmake package.xml
It can get tedious to type out an entire package name. In the previous example, roscpp_tutorials is a fairly long name. Luckily, some ROS tools support TAB completion.
Start by typing:
# roscd catk<<< now push the TAB key >>>
After pushing the TAB key, the command line should fill out the rest:
$ roscd catkin/
This works because
catkin is currently the only ROS package that starts with
You may have noticed a pattern with the naming of the ROS tools:
rospack= ros + pack(age)
roscd= ros + cd
rosls= ros + ls
This naming pattern holds for many of the ROS tools.
ROS strongly relays on the shell environment variables. Make sure that everything is configured as expected:
root@erlerobot:~/catkin_ws/devel# export|grep ROS declare -x ROS_DISTRO="groovy" declare -x ROS_ETC_DIR="/opt/ros/groovy/etc/ros" declare -x ROS_MASTER_URI="http://localhost:11311" declare -x ROS_PACKAGE_PATH="/root/catkin_ws/src:/opt/ros/groovy/share:/opt/ros/groovy/stacks" declare -x ROS_ROOT="/opt/ros/groovy/share/ros" declare -x ROS_TEST_RESULTS_DIR="/root/catkin_ws/build/test_results"
Now that you can get around in ROS, let's create a package.