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So I have a setup where I want to launch my ROS nodes via a launch file, which in turn will ssh into a udoo board and the launch the necessary files for hardware communication. The launch file works great normally when I do roslaunch, and I have set up a passwordless connection between the PC running ROS and udoo, using the ssh-rsa protocol. I wanted to launch this on the robot upstart so used the robot-upstart package to create a service for launching. This is where my errors start, as the service does not be able to establish a ssh connection between the PC running ROS and the udoo board. The error is as follows:

 Jan 09 15:12:26 seven-robot-2 systemd[1]: Started "bringup test_ru_launch".
    Jan 09 15:12:26 seven-robot-2 root[3298]: test_ru_launch: Using workspace setup file /home/seven-robot-2/Seven_ROS/devel/setup.bash
    Jan 09 15:12:26 seven-robot-2 test_ru_launch-start[3297]: <14>Jan  9 15:12:26 root: test_ru_launch: Using workspace setup file /home/seven-robot-2/Seven_ROS/devel/setup.bash
    Jan 09 15:12:27 seven-robot-2 test_ru_launch-start[3297]: <14>Jan  9 15:12:27 root: test_ru_launch: Launching ROS_HOSTNAME=seven-robot-2, ROS_IP=, ROS_MASTER_URI=http://sevenrobot2:11311/, ROS_HOME=/root/.ros, ROS_LOG_DIR=/tmp
Jan 09 15:12:27 seven-robot-2 test_ru_launch-start[3297]: ls: cannot access '/etc/ros/melodic/test_ru_launch.d/*.xacro': No such file or directory
    Jan 09 15:12:27 seven-robot-2 test_ru_launch-start[3297]: <14>Jan  9 15:12:27 root: test_ru_launch: Generated launchfile: /tmp/test_ru_launch.launch
    Jan 09 15:12:27 seven-robot-2 root[3359]: test_ru_launch: Started roslaunch as background process, PID 3358, ROS_LOG_DIR=/tmp
    Jan 09 15:12:27 seven-robot-2 test_ru_launch-start[3297]: <14>Jan  9 15:12:27 root: test_ru_launch: Started roslaunch as background process, PID 3358, ROS_LOG_DIR=/tmp
    Jan 09 15:12:28 seven-robot-2 test_ru_launch-start[3297]: xacro: in-order processing became default in ROS Melodic. You can drop the option.
    Jan 09 15:12:29 seven-robot-2 test_ru_launch-start[3297]: remote[192.168.2.23-0]: failed to launch on udooqdl:
    Jan 09 15:12:29 seven-robot-2 test_ru_launch-start[3297]: Unable to establish ssh connection to [[email protected]:22]: Server u'192.168.2.23' not found in known_hosts
    Jan 09 15:12:29 seven-robot-2 test_ru_launch-start[3297]: 
    Jan 09 15:12:29 seven-robot-2 test_ru_launch-start[3297]: RLException: unable to start remote roslaunch child: 192.168.2.23-0
    Jan 09 15:12:29 seven-robot-2 test_ru_launch-start[3297]: The traceback for the exception was written to the log file
    Jan 09 15:12:29 seven-robot-2 test_ru_launch-start[3297]: ... logging to /tmp/edd14b60-9001-11ed-8c81-7c8334b0242e/roslaunch-seven-robot-2-3358.log
    Jan 09 15:12:29 seven-robot-2 test_ru_launch-start[3297]: Checking log directory for disk usage. This may take a while.
    Jan 09 15:12:29 seven-robot-2 test_ru_launch-start[3297]: Press Ctrl-C to interrupt
    Jan 09 15:12:29 seven-robot-2 test_ru_launch-start[3297]: Done checking log file disk usage. Usage is <1GB.
    Jan 09 15:12:29 seven-robot-2 test_ru_launch-start[3297]: [31B blob data]
    Jan 09 15:12:29 seven-robot-2 test_ru_launch-start[3297]: started roslaunch server http://seven-robot-2:46315/
    Jan 09 15:12:29 seven-robot-2 test_ru_launch-start[3297]: remote[192.168.2.23-0] starting roslaunch
    Jan 09 15:12:29 seven-robot-2 test_ru_launch-start[3297]: remote[192.168.2.23-0]: creating ssh connection to 192.168.2.23:22, user[root]
    Jan 09 15:12:29 seven-robot-2 test_ru_launch-start[3297]: [192.168.2.23-0] killing on exit
    Jan 09 15:12:29 seven-robot-2 systemd[1]: test_ru_launch.service: Main process exited, code=exited, status=1/FAILURE
    Jan 09 15:12:29 seven-robot-2 systemd[1]: test_ru_launch.service: Failed with result 'exit-code'.
    Jan 09 15:12:29 seven-robot-2 systemd[1]: test_ru_launch.service: Service hold-off time over, scheduling restart.

The service and launch file is as follows:

Service file:

# THIS IS A GENERATED FILE, NOT RECOMMENDED TO EDIT.

[Unit]
Description="bringup test_ru_launch"
After=network.target
Wants=network.target
After=network-online.target
Wants=network-online.target
After=multi-user.target
Wants=multi-user.target


[Service]
Type=simple
ExecStart=/usr/sbin/test_ru_launch-start
Restart=on-failure

[Install]
WantedBy=graphical.target

roslaunch file (part where ssh is established):

<group>
        <machine name="udooqdl" address="192.168.2.23" user="root" env-loader="/home/root/Seven_ROS/env_loader_udooqdl.sh" default="true"/>
      <rosparam file="$(find seven_robot_base)/params/robotParams.yaml" command="load" ns="$(arg uavcanNs)/uavcan_ros_bridge"/>
      <rosparam file="$(find seven_robot_localization)/params/diff_drive.yaml" command="load" ns="$(arg uavcanNs)/uavcan_ros_bridge"/>
      <include file="$(find uavcan_ros_bridge)/launch/uavcan_ros_bridge.launch">
        <arg name="uavcanNs" value="$(arg uavcanNs)"/>
        <arg name="laser_enabled" default="$(arg enable_Laser)"/>
        <arg name="publishuavcanTf" default="$(arg publishcanTf)"/>
        <arg name="enableMotors" default="$(arg motors_enabled)"/>
      </include>
    </group>

Not sure what is causing the error, any help/suggestions is appreciated. Happy to provide more information if needed. I am running ROS melodic on Ubuntu 18.04.

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1 Answer 1

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The core error in your text is: Server u'192.168.2.23' not found in known_hosts

There are two steps to establishing an SSH connection. First you need to establish the connection and after that you present your credentials.

To avoid the risk of a man-in-the-middle attack. It is standard for ssh clients to keep track of the cryptographic fingerprint of the remote server and refuse to connect if either there's not already a fingerprint for that server or it is different on the local machine.

When doing this interactively you will typically prompt you to add a new key to the known_hosts file.

This answer has an example of what it will look like

The authenticity of host 'server-name (12.345.678.900)' can't be established.
RSA key fingerprint is XXXXXXX.
Are you sure you want to continue connecting (yes/no)?

And the solution to your problem is to setup the known_hosts for target machine. Note that it's specific to the machine, the user, and I believe the specific protocol. (Aka roslaunch uses RSA by default which may not be the default for your command line ssh client anymore.

Make sure to test add the user of the machine. That's a common mistake when debugging.

There's also a very similar question here: A is not in your SSH known_hosts file. as a good reference.

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  • $\begingroup$ Hey thanks a lot for your answer, we were able to solve it yesterday. So the issue turned out to be the fact that, this particular service launched as root, but we had established ssh with the remote machine as a user. Creating new keys and establishing it as the root seemed to fix the issue. I have accepted your answer, but if you can update it to just check which user is ssh-ing and are credentials set for that user, I think it will be helpful for other people in the future. $\endgroup$
    – Pran-7
    Jan 11, 2023 at 6:15
  • $\begingroup$ Thanks, I mentioned that it was user specific already. Hopefully your comment will help people find this quicker. $\endgroup$
    – Tully ♦
    Jan 12, 2023 at 10:27

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