Running discovery process as root breaks existing processes running as normal user when SHM is used

[ksuszka]

Is there an already existing issue for this?

• I have searched the existing issues

Expected behavior

Running an arbitrary ROS command as a root should not break existing ROS ecosystem running under a non-root user.

Current behavior

Running an arbitrary ROS command under SHM transport as a root breaks service discovery for ROS nodes running as a non-root user.

Steps to reproduce

Open four terminals. In the first terminal, start publishing messages as a non-root user:

docker run -it --net=host --privileged --ipc=host -u 5678 -e HOME=/tmp ros:humble ros2 topic pub /foo std_msgs/msg/String "data: foo"

In the second terminal, start a process to retrieve messages as as the same non-root user

docker run -it --net=host --privileged --ipc=host -u 5678 -e HOME=/tmp ros:humble ros2 topic hz /foo

You should see proper output, as expected.

In the third terminal, run some ROS command as a root:

docker run -it --net=host --privileged --ipc=host -u 0 ros:humble ros2 topic hz /foo

You should see WARNING: topic [/foo] does not appear to be published yet - it is not preferable, but can be explained by other issues like #2624 (comment)

In the fourth terminal, run the same command as in the second step:

docker run -it --net=host --privileged --ipc=host -u 5678 -e HOME=/tmp ros:humble ros2 topic hz /foo

This time, you will see WARNING: topic [/foo] does not appear to be published yet.
The previous command broke discovery of existing nodes.

Fast DDS version/commit

ros-humble-fastrtps-cmake-module/now 2.2.0-2jammy.20230112.142430 amd64 [installed,local]
ros-humble-fastrtps/now 2.6.4-1jammy.20230117.223829 amd64 [installed,local]
ros-humble-rmw-fastrtps-cpp/now 6.2.2-1jammy.20230117.225910 amd64 [installed,local]
ros-humble-rmw-fastrtps-shared-cpp/now 6.2.2-1jammy.20230117.225455 amd64 [installed,local]
ros-humble-rosidl-typesupport-fastrtps-c/now 2.2.0-2jammy.20230112.145514 amd64 [installed,local]
ros-humble-rosidl-typesupport-fastrtps-cpp/now 2.2.0-2jammy.20230112.145146 amd64 [installed,local]

Platform/Architecture

Other. Please specify in Additional context section.

Transport layer

Default configuration, UDPv4 & SHM

Additional context

This is yet another issue related to the shared memory transport in FastDDS (other related issues I found: ros2/ros2cli#598, #1750, #2624). However this experiment shows that the issue occurs not only when new connections between different users are established but can affect the service discovery for a single user.

XML configuration file

No response

Relevant log output

No response

Network traffic capture

No response

[JesusPoderoso]

Hi @ksuszka, thanks for the report.
We were able to replicate the issue, and recently we updated the documentation warning about the possible issues when launching any of the processes with a higher permission.
This issue is now categorized as bug, and we will look for solving this.

[maxpolzin]

I have also encountered this issue.

For me it works to:

1. start the container with these options: --network=host --ipc=host --pid=host
2. run nodes inside the container with the same user id as nodes on the host

For convenience, I have created this repository with my setup to build (as root user) and run (with host's user id) ROS 2 packages/ nodes inside containers. This allows to use Shared Memory Transport (SHM) between ROS 2 nodes run inside the container and on the host.

https://github.com/rosblox/ros-template