ROS 2 CLIが結果を表示しない場合の原因と解決策

概要
現象
結論
説明
参考

概要

ROS 2でCLIコマンド（例：ros2 topic listやros2 node list）を実行した際に、結果が取得できないことがありました。本記事では、その際の対処方法について説明します。

現象

ros2 topic listを実行後、2〜3分待機すると、以下のような「Connection timed out」エラーが表示されました。

Traceback (most recent call last):
  File "/opt/ros/humble/bin/ros2", line 33, in 
    sys.exit(load_entry_point('ros2cli==0.18.11', 'console_scripts', 'ros2')())
  File "/opt/ros/humble/lib/python3.10/site-packages/ros2cli/cli.py", line 91, in main
    rc = extension.main(parser=parser, args=args)
  File "/opt/ros/humble/lib/python3.10/site-packages/ros2topic/command/topic.py", line 41, in main
    return extension.main(args=args)
  File "/opt/ros/humble/lib/python3.10/site-packages/ros2topic/verb/list.py", line 55, in main
    with NodeStrategy(args) as node:
  File "/opt/ros/humble/lib/python3.10/site-packages/ros2cli/node/strategy.py", line 27, in __init__
    if use_daemon and is_daemon_running(args):
  File "/opt/ros/humble/lib/python3.10/site-packages/ros2cli/node/daemon.py", line 75, in is_daemon_running
    return node.connected
  File "/opt/ros/humble/lib/python3.10/site-packages/ros2cli/node/daemon.py", line 46, in connected
    for method in self._proxy.system.listMethods()
  File "/usr/lib/python3.10/xmlrpc/client.py", line 1122, in __call__
    return self.__send(self.__name, args)
  File "/usr/lib/python3.10/xmlrpc/client.py", line 1464, in __request
    response = self.__transport.request(
  File "/usr/lib/python3.10/xmlrpc/client.py", line 1166, in request
    return self.single_request(host, handler, request_body, verbose)
  File "/usr/lib/python3.10/xmlrpc/client.py", line 1178, in single_request
    http_conn = self.send_request(host, handler, request_body, verbose)
  File "/usr/lib/python3.10/xmlrpc/client.py", line 1291, in send_request
    self.send_content(connection, request_body)
  File "/usr/lib/python3.10/xmlrpc/client.py", line 1321, in send_content
    connection.endheaders(request_body)
  File "/usr/lib/python3.10/http/client.py", line 1278, in endheaders
    self._send_output(message_body, encode_chunked=encode_chunked)
  File "/usr/lib/python3.10/http/client.py", line 1038, in _send_output
    self.send(msg)
  File "/usr/lib/python3.10/http/client.py", line 976, in send
    self.connect()
  File "/usr/lib/python3.10/http/client.py", line 942, in connect
    self.sock = self._create_connection(
  File "/usr/lib/python3.10/socket.py", line 845, in create_connection
    raise err
  File "/usr/lib/python3.10/socket.py", line 833, in create_connection
    sock.connect(sa)
TimeoutError: [Errno 110] Connection timed out