ROS FAQ & Troubleshooting

This page reference ROS and ROS 2 snap common questions and troubleshooting:

Frequently Asked Questions

If you cannot find an answer to your question here, feel free to ask it on the snapcraft forum.

I cannot snap my application. What should I check?
- Snapcraft uses the familiar ROS tools (rosdep/catkin/colcon etc). Which means that your application must follow the ROS directives for proper packaging, such as declaring all the necessary dependencies in the package.xml files or the install rules in your CMake file. Make sure that these are in good order before attempting to create a snap.
Which base should I use, Core18 or Core20?
- You should use the base that corresponds to your ROS version. That is, Core18 for ROS Melodic and Core20 for ROS Noetic and ROS2 Foxy.
For ROS1, do I have to expose roscore from my snap?
- Exposing a roslaunch command from your snap will automatically launch a roscore if needed. The only reason to expose explicitly the roscore would be if you plan to start the roscore explicitly from your snap.
Where should my snapcraft.yaml file live?
- Within the package:
  - In Core20 the snap/ directory should be located at the root of the package (next to your package.xml file)
  - In Core18 the snap/ directory should be located either one folder behind your package root or at the root of your workspace
- Outside the package:
  - Using a rosinstall file to download the sources.
  - Using a single git repository holding the sources.

Troubleshooting

Rosrun and roslaunch are not available in my snap.
- If this happens, it means that your ROS project does not define a runtime dependency on either rosrun nor roslaunch at any place. You can fix this by either properly declaring the dependency in the appropriate ROS package.xml file. Another option is to declare either (or both) ROS packages as stage-packages in your snapcraft.yaml. The ROS packages for rosrun and roslaunch respectively are: ros-${ROS-DISTRO}-rosbash and ros-${ROS-DISTRO}-roslaunch.
With Core18 Catkin plugin creates an external link that prevents the security checks to pass.
- Please see: Catkin generating an external link.
Executing ROS python code is missing python dependencies.
- The path to the libraries lapack and blas is by default not included in the library path. Thus, it must be extended manually.
```
environment:
  "LD_LIBRARY_PATH": "$LD_LIBRARY_PATH:$SNAP/usr/lib/$SNAPCRAFT_ARCH_TRIPLET/blas:$SNAP/usr/lib/$SNAPCRAFT_ARCH_TRIPLET/lapack"
```
When building your snap, you might see this warning: “This part is missing libraries that cannot be satisfied with any available stage-packages known to snapcraft”.
- Some libraries are build-time only dependencies, but are still reported as run-time dependencies by snapcraft. This warning is a false positive and will be fixed soon in snapcraft. When snapping ros2-demo you might encounter:
```
This part is missing libraries that cannot be satisfied with any available stage-packages known to snapcraft:
# false-positive, none of the following are necessary at run-time
libnddsc.so
libnddscore.so
libnddscpp.so
librosidl_typesupport_connext_c.so
librosidl_typesupport_connext_cpp.so
librticonnextmsgcpp.so
```
Strictly confined ROS 2 snaps shows an access error regarding shared memory.
If you see something similar to:
```
[RTPS_TRANSPORT_SHM Error] Failed to create segment 86bb3c83d0835208: Permission denied -> Function compute_per_allocation_extra_size
[RTPS_MSG_OUT Error] Permission denied -> Function init
```
ROS 2 communication library is trying to use the shared memory mechanism. ROS2 shared memory is not yet working with snap. But don’t worry, even if you see this error, the messages are going to be transmitted (just not through shared memory).

Last updated a month ago.

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