Arch/GNS3：无法连接到端口 3080 上的 127.0.0.1：[Errno 111] 连接被拒绝

Question

我在 Arch 上安装了 GNS3，如下所示这和这。我已经重启了机器，但它一直提示无法连接到本地主机的 3080 端口。默认情况下，当 GNS3 没有运行时，端口不打开：

$ ss -tlp | grep 3080
$

下面的最后一行说明了一些东西，不是吗？

ImportError: cannot import name 'WordCompleter' from 'prompt_toolkit.contrib.completers' (/usr/lib/python3.7/site-packages/prompt_toolkit/contrib/completers/__init__.py)

下面是包含 GUI 错误和 GNS3 Doctor（帮助 -> GNS3 Doctor）的屏幕截图。

当我运行它时（以普通用户或 root 身份），它显示：

$ gns3
2019-08-11 19:37:33 INFO root:126 Log level: INFO
2019-08-11 19:37:33 INFO main:259 GNS3 GUI version 2.1.21
2019-08-11 19:37:33 INFO main:260 Copyright (c) 2007-2019 GNS3 Technologies Inc.
2019-08-11 19:37:33 INFO main:262 Application started with /usr/bin/gns3
2019-08-11 19:37:38 ERROR local_server:489 Local server process has stopped
2019-08-11 19:37:38 ERROR local_server:491 Traceback (most recent call last):
  File "/usr/bin/gns3server", line 10, in <module>
    sys.exit(main())
  File "/usr/lib/python3.7/site-packages/gns3server/main.py", line 82, in main
    from gns3server.run import run
  File "/usr/lib/python3.7/site-packages/gns3server/run.py", line 32, in <module>
    from gns3server.web.web_server import WebServer
  File "/usr/lib/python3.7/site-packages/gns3server/web/web_server.py", line 36, in <module>
    from .route import Route
  File "/usr/lib/python3.7/site-packages/gns3server/web/route.py", line 30, in <module>
    from ..compute.error import NodeError, ImageMissingError
  File "/usr/lib/python3.7/site-packages/gns3server/compute/__init__.py", line 24, in <module>
    from .dynamips import Dynamips
  File "/usr/lib/python3.7/site-packages/gns3server/compute/dynamips/__init__.py", line 46, in <module>
    from .dynamips_factory import DynamipsFactory
  File "/usr/lib/python3.7/site-packages/gns3server/compute/dynamips/dynamips_factory.py", line 28, in <module>
    from .nodes.ethernet_switch import EthernetSwitch
  File "/usr/lib/python3.7/site-packages/gns3server/compute/dynamips/nodes/ethernet_switch.py", line 25, in <module>
    from gns3server.utils.asyncio.embed_shell import EmbedShell, create_telnet_shell
  File "/usr/lib/python3.7/site-packages/gns3server/utils/asyncio/embed_shell.py", line 26, in <module>
    from prompt_toolkit.contrib.completers import WordCompleter
ImportError: cannot import name 'WordCompleter' from 'prompt_toolkit.contrib.completers' (/usr/lib/python3.7/site-packages/prompt_toolkit/contrib/completers/__init__.py)

2019-08-11 19:38:03 CRITICAL utils.progress_dialog:181 WaitForConnectionWorker thread stopping with an error: Could not connect to 127.0.0.1 on port 3080: [Errno 111] Connection refused
2019-08-11 19:38:03 CRITICAL progress_dialog.py:183 Could not connect to 127.0.0.1 on port 3080: [Errno 111] Connection refused