ROS on Ubuntu Core Issues

Question

I am having some problems with Ubuntu Core and ROS. I am using Snapcraft. I was able to do the "create your first snap" tutorial (https://snapcraft.io/docs/build-snaps/your-first-snap) and everything was fine.

Then I followed the ROS tutorial (https://github.com/snapcore/snapcraft/blob/master/docs/ros-snap.md). Instead of doing a talker and a listener I just have one "hello world" node that outputs a message to the screen. I am able to build and install just fine, but on running I get the following output:

$USER@localhost:~$ ros-example.launch-project  
... logging to /home/$USER/snap/ros-example/x1/ros/log/a413e04a-efb3-11e6-bf45-3d232f894a41/roslaunch-localhost.localdomain-7392.log 
Checking log directory for disk usage. This may take awhile. 
Press Ctrl-C to interrupt

Traceback (most recent call last):   
  File "/snap/ros-example/x1/opt/ros/kinetic/lib/python2.7/dist-packages/roslaunch/__init__.py", line 307, in main
      p.start()   
  File "/snap/ros-example/x1/opt/ros/kinetic/lib/python2.7/dist-packages/roslaunch/parent.py", line 268, in start
    self._start_infrastructure()
  File "/snap/ros-example/x1/opt/ros/kinetic/lib/python2.7/dist-packages/roslaunch/parent.py", line 217, in _start_infrastructure
    self._load_config()   
  File "/snap/ros-example/x1/opt/ros/kinetic/lib/python2.7/dist-packages/roslaunch/parent.py", line 132, in _load_config
    roslaunch_strs=self.roslaunch_strs, verbose=self.verbose)   
  File "/snap/ros-example/x1/opt/ros/kinetic/lib/python2.7/dist-packages/roslaunch/config.py", line 471, in load_config_default
    config.assign_machines()   
  File "/snap/ros-example/x1/opt/ros/kinetic/lib/python2.7/dist-packages/roslaunch/config.py", line 222, in assign_machines
    if [m for m in machine_unify_dict.values() if not is_machine_local(m)]:   
  File "/snap/ros-example/x1/opt/ros/kinetic/lib/python2.7/dist-packages/roslaunch/core.py", line 97, in is_machine_local
    local_addresses = ['localhost'] + rosgraph.network.get_local_addresses()   
  File "/snap/ros-example/x1/opt/ros/kinetic/lib/python2.7/dist-packages/rosgraph/network.py", line 218, in get_local_addresses
    for iface in netifaces.interfaces(): 
OSError: [Errno 13] Permission denied

I have added the install rules for the .cpp, .hpp, and .launch files in the cmake list, and running the roslaunch command works to run the node. But running in the Core environment as a snap does not work. Any suggestions would be greatly appreciated.

Here's my cmakelist:

cmake_minimum_required(VERSION 2.8.3)
project(hello_world)

find_package(catkin REQUIRED COMPONENTS
  roscpp
  rospy
  std_msgs
)

catkin_package()

include_directories(${catkin_INCLUDE_DIRS})

add_executable(write_prompt src/write_prompt.cpp)
target_link_libraries(write_prompt ${catkin_LIBRARIES})

install(TARGETS write_prompt
  ARCHIVE DESTINATION ${CATKIN_PACKAGE_LIB_DESTINATION}
  LIBRARY DESTINATION ${CATKIN_PACKAGE_LIB_DESTINATION}
  RUNTIME DESTINATION ${CATKIN_PACKAGE_BIN_DESTINATION}
)

install(DIRECTORY include/${PROJECT_NAME}/
  DESTINATION ${CATKIN_PACKAGE_INCLUDE_DESTINATION}
  FILES_MATCHING PATTERN "*.h"
  PATTERN "*.hpp"
  PATTERN ".svn" EXCLUDE
)

install(FILES
  launch/run_code.launch
  DESTINATION ${CATKIN_PACKAGE_SHARE_DESTINATION}
)

And my snapcraft.yaml:

name: ros-example
version: 1.0
summary: ROS Example
description: Runs a modified Hello World node
confinement: strict

apps:
  launch-project:
    command: roslaunch hello_world run_code.launch

parts:
  ros-project:
    plugin: catkin
    source: .
    catkin-packages:
      - hello_world
    rosdistro: kinetic

Answer 1

You're so close! Your snap isn't requesting access to the network, which by default snaps do not get. You do this by setting the plugs property of the app in question. Try making your apps section look like this:

apps:
  launch-project:
    command: roslaunch hello_world run_code.launch
    plugs: [network, network-bind]

Once you install that, run snap interfaces and you'll see both the network and network-bind plugs connected to the core's slot. To learn more about these, check out the snapd interfaces wiki.

As an extra exercise, once it's working, try disconnecting the interfaces:

sudo snap disconnect ros-example:network
sudo snap disconnect ros-example:network-bind

And run your app again. You should see it fail again with the same error.

As a final note, while you're developing/testing things out, remember you can install with --devmode to skip confinement: sudo snap install --devmode <my snap>.