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 ubuntu 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 CMakeFile.txt. Make sure that these are in good order before attempting to create a snap.

Which base should I use (core18, core20, core22 or core24)?

• You should use the base that corresponds to your ROS version. That is,
  • core18 for ROS Melodic and ROS 2 Dashing.
  • core20 for ROS Noetic and ROS 2 Foxy.
  • core22 for ROS 2 Humble.
  • core24 for ROS 2 Jazzy.

For ROS 1, 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 and above, 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.

Can my snap save data on the host?

• The snap define some environment variables for data and file storage pointing to different locations that a snap can write to depending on the use case of your data.
• You can save data that are common across revisions of a snap. These directories won’t be backed-up and restored across revisions:
  • $SNAP_COMMON, typical value: /var/snap/hello-world/common. Owned by root
  • $SNAP_USER_COMMON, typical value: /home/$USER/snap/hello-world/common. Owned by $USER
• You can save data for a revision of a snap. This directory is backed up and restored across revisions:
  • $SNAP_DATA, typical value: /var/snap/hello-world/27. Owned by root
  • $SNAP_USER_DATA, typical value: /home/$USER/snap/hello-world/27. Owned by $USER
• Additionally, with the home interface, your snap could access the real $HOME of the user by accessing $SNAP_REAL_HOME.

Troubleshooting

The command(s) rosrun and/or 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 anywhere. You can fix this by declaring the dependency in the appropriate ROS package.xml file. Another option is to list either (or both) ROS packages as stage-packages in your snapcraft.yaml. The ROS packages for rosrun and roslaunch are respectively:
  • ros-${ROS-DISTRO}-rosbash
  • ros-${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 .

Missing lapack and/or blas.

• Paths to the libraries lapack and blas are not included in the library path by default. Thus, it must be extended manually in your app.

  environment:
    "LD_LIBRARY_PATH": "$LD_LIBRARY_PATH:$SNAP/usr/lib/$SNAPCRAFT_ARCH_TRIPLET/blas:$SNAP/usr/lib/$SNAPCRAFT_ARCH_TRIPLET/lapack"
  

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. For instance, 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. Don’t worry, even if you see this error, the messages are going to be transmitted (just not through shared memory). If you want to use the shared memory of ROS 2 within snap, visit: ROS 2 shared memory in snap

At runtime, the snap shows an error similar to :

[rospack] Unable to create temporary cache file /home/USER/.ros/.rospack_cache.VyyWPF: Permission denied

• By default rospack and roslog write to the $HOME/.ros. When strictly confined a snap who doesn’t have the home interface cannot access the host $HOME. Also, even with the home plug the snap cannot access to hidden directories (.directories) for security reasons (like .ssh).
  • To solve that, we can write ROS logs in the $SNAP_USER_DATA environment variable. We can do so by defining the ROS environment variable ROS_HOME. We can do so by adding to a snap app in the snapcraft.yaml:

        [...]
        apps:
          myapp:
            environment:
              ROS_HOME: $SNAP_USER_DATA/ros
            command: [...]
    

  • The data will also be available from the host in: ~/snap/YOUR_SNAP_NAME/current/ros.

Calling snapcraft give the following error:

Failed to install GPG key: unable to establish connection to key server 'keyserver.ubuntu.com'

Recommended resolution:
Verify any configured GPG keys.

Detailed information:
GPG key ID: C1CF6E31E6BADE8868B172B4F42ED6FBAB17C654
GPG key server: keyserver.ubuntu.com

• If the problem is persistent, it’s most probably a DNS issue.
  • To verify if it’s a DNS issue, if the following command succeeds it’s most probably a DNS issue:sudo -E apt-key adv --keyserver 'hkp://keyserver.ubuntu.com:80' --recv-key C1CF6E31E6BADE8868B172B4F42ED6FBAB17C654
  • We can also verify that the port 11371 is not blocked or occupied.

ROS snap with shared memory doesn’t receive or send data on topic:

• If you have properly followed the ROS snap and shared memory how to guide but still have problem, make sure that the differents processes publishing/subscribing ROS 2 data over shared memory are using the same USER. FastDDS shared memory can generate communication problems if acces from different users.
• Keep in mind that snap services are running with the root user while CLI applications might use a less privileged user (i.e: ubuntu) causing the FastDDS shared memory communication problems.