How to execute a script at shutdown of a launch process

Question

I am trying to execute a bash script when my robotic simulation is shut down (to tear down the network configuration necessary for the simulation).

I use ROS2 launch system to do so and I planned on using the OnShutdown event handler to launch some ROS actions when I ctrl-C the launch system.

However, I fail to execute anything else than a LogInfo action in this callback:

Example launch file:

import os
from launch import LaunchDescription
from launch.actions import ExecuteProcess, LogInfo, RegisterEventHandler
from launch.event_handlers import OnShutdown
from launch_ros.actions import Node
from launch.substitutions import LocalSubstitution
def generate_launch_description():
talker_node = Node(
        package='demo_nodes_cpp',
        executable='talker',
        name='demo_talker',
    )

ld = LaunchDescription([
    talker_node,
    RegisterEventHandler(
        OnShutdown(
            on_shutdown=[
                LogInfo(
                    msg=['Launch was asked to shutdown: ', LocalSubstitution('event.reason')]
                ),
                ExecuteProcess(
                    cmd=['echo', 'Hello from ExecuteProcess']
                )
            ]
        )
    )
])

return ld

This will give the following output. It ignores the echo command entirely, but executes LogInfo properly.

theotime@theotime-Precision-5570:~/simulation_ws$ ros2 launch src/launch/test_launch.py --show-all-subprocesses-output 
[INFO] [launch]: All log files can be found below /home/theotime/.ros/log/2023-06-20-15-25-59-974180-theotime-Precision-5570-170652
[INFO] [launch]: Default logging verbosity is set to INFO
[INFO] [talker-1]: process started with pid [170653]
[talker-1] [INFO] [1687267561.062017969] [demo_talker]: Publishing: 'Hello World: 1'
[talker-1] [INFO] [1687267562.061961754] [demo_talker]: Publishing: 'Hello World: 2'
[talker-1] [INFO] [1687267563.061974971] [demo_talker]: Publishing: 'Hello World: 3'
^C[WARNING] [launch]: user interrupted with ctrl-c (SIGINT)
[INFO] [launch.user]: Launch was asked to shutdown: ctrl-c (SIGINT)
[talker-1] [INFO] [1687267563.397639727] [rclcpp]: signal_handler(signum=2)
[INFO] [talker-1]: process has finished cleanly [pid 170653]

Why does OnShutdown refuse to execute actions other than LogInfo?

How can I execute a bash script on shutdown of a launch process ?

For reference and convenience: Link to the code responsible for OnShutdown

Answer 1

I can reproduce this. I don't have advice about the root cause, but it looks like you can provide a callable to the on_shutdown= argument which might work for your use case.

For example, I can define:

def shutdown_func_with_echo_side_effect(event, context):
    os.system('echo [os.system()] Shutdown callback function can echo this way.')
    return [
        LogInfo(msg='Shutdown callback was called for reason "{}"'.format(event.reason)),
        ExecuteProcess(cmd=['echo', 'However, this echo will fail.'])]

and register it with the OnShutdown event handler like this:

ld = LaunchDescription([
        talker_node,
        RegisterEventHandler(
            OnShutdown(on_shutdown=shutdown_func_with_echo_side_effect)
        )
    ])

This gives

[INFO] [launch]: All log files can be found below <path to logs>
[INFO] [launch]: Default logging verbosity is set to INFO
[INFO] [talker.EXE-1]: process started with pid [19092]
[talker.EXE-1] [INFO] [1687924816.372554600] [demo_talker]: Publishing: 'Hello World: 1'
[talker.EXE-1] [INFO] [1687924817.377274200] [demo_talker]: Publishing: 'Hello World: 2'
[talker.EXE-1] [INFO] [1687924818.367993100] [demo_talker]: Publishing: 'Hello World: 3'
[talker.EXE-1] [INFO] [1687924819.381295400] [demo_talker]: Publishing: 'Hello World: 4'
[WARNING] [launch]: user interrupted with ctrl-c (SIGINT)
[os.system()] Shutdown callback function can echo this way.
[INFO] [launch.user]: Shutdown callback was called for reason "ctrl-c (SIGINT)"
[INFO] [talker.EXE-1]: process has finished cleanly [pid 19092]

Like your example, the ExecuteProcess action returned by the function does not appear to do anything.