最近发现我的Ubuntu服务器的"Software & Updates"无法打开。网上有各种解决方案，“不幸”的是没一个能起作用，“幸运”的是答案大方向是对的。最终结合一些诊断手段解决了该问题。像这种网上给个大概方向，然后结合自身状况，进一步诊断和解决问题的模式，应该是日常工作中的常态。本文分享一下这个过程。
Ubuntu服务器"Software & Updates"无法打开是指：
- 通过应用搜索找到"Software & Updates"或者"Settings->About->Software Updates"（见下图的位置），点击按钮会没有任何反应。
- 如果在"Terminal"里执行
sudo software-properties-gtk，会有错误信息：
1ERROR:dbus.proxies:Introspect error on :1.239:/: dbus.exceptions.DBusException: org.freedesktop.DBus.Error.NoReply: Message recipient disconnected from message bus without replying
2Traceback (most recent call last):
3 File "/usr/bin/software-properties-gtk", line 100, in <module>
4 app = SoftwarePropertiesGtk(datadir=options.data_dir, options=options, file=file)
5 File "/usr/lib/python3/dist-packages/softwareproperties/gtk/SoftwarePropertiesGtk.py", line 222, in __init__
6 self.backend.Reload();
7 File "/usr/lib/python3/dist-packages/dbus/proxies.py", line 72, in __call__
8 return self._proxy_method(*args, **keywords)
9 File "/usr/lib/python3/dist-packages/dbus/proxies.py", line 141, in __call__
10 return self._connection.call_blocking(self._named_service,
11 File "/usr/lib/python3/dist-packages/dbus/connection.py", line 652, in call_blocking
12 reply_message = self.send_message_with_reply_and_block(
13dbus.exceptions.DBusException: org.freedesktop.DBus.Error.ServiceUnknown: The name :1.239 was not provided by any .service files
网上搜索dbus.exceptions.DBusException: org.freedesktop.DBus.Error.ServiceUnknown能看到不少相关解答。比如Ubuntu 18.04 software-properties-gtk failing with org.freedesktop.DBus.Error.ServiceUnknown，再比如Software & Updates won’t launch at all，还有App “Software & Updates” not responding。尝试后，均不能解决我的问题，但是能得到一些确定性的提示：
software-properties-gtk通过系统dbus执行- 通过
sudo journalctl -u dbus -b可以查看dbus日志（注意：sudo十分重要，因为查看的是系统服务dbus的日志），从而发现导致software-properties-gtk失败的原因 - 失败原因是某些
python包“不正常”导致software-properties-gtk找不到requests_unixsocket（见如下日志片段）
1Traceback (most recent call last):
2 File "/usr/lib/software-properties/software-properties-dbus", line 68, in <module>
3 server = SoftwarePropertiesDBus(bus, datadir=datadir)
4 File "/lib/python3/dist-packages/softwareproperties/dbus/SoftwarePropertiesDBus.py", line 66, in __init__
5 self._livepatch_service = LivepatchService()
6 File "/lib/python3/dist-packages/softwareproperties/LivepatchService.py", line 93, in __init__
7 self._session = requests_unixsocket.Session()
8NameError: name 'requests_unixsocket' is not defined
网上答案推荐重新安装相关python包，例如：sudo apt install --reinstall python3-six python3-certifi python3-requests python3-idna。显然，我的操作系统有问题的包不是这几个，所以操作后依旧不能让requests-unixsocket被正常import。根据手上信息，我的目标就很明确了，找到实际损坏的包，重新安装。于是用sudo vim /lib/python3/dist-packages/softwareproperties/LivepatchService.py查看这个文件到底是如何importrequests-unixsocket。发现最开始的地方，尝试import requests_unixsocket，而导致失败的异常被try-except“吞掉了”。
1try:
2 import dateutil.parser
3 import requests_unixsocket
4
5 gi.require_version('Snapd', '1')
6 from gi.repository import Snapd
7except(ImportError, ValueError):
8 pass
于是我直接修改该文件，在except捕捉到异常后，打印相关信息
1except(ImportError, ValueError):
2 import traceback
3 print(traceback.format_exc())
再次运行sudo software-properties-gtk，失败后查看日志，终于发现是因为urllib3有问题：
1 import requests_unixsocket
2 File "/lib/python3/dist-packages/requests_unixsocket/__init__.py", line 1, in <module>
3 import requests
4 File "/lib/python3/dist-packages/requests/__init__.py", line 43, in <module>
5 import urllib3
6ModuleNotFoundError: No module named 'urllib3'
7Traceback (most recent call last):
8 File "/usr/lib/software-properties/software-properties-dbus", line 68, in <module>
9 server = SoftwarePropertiesDBus(bus, datadir=datadir)
10 File "/lib/python3/dist-packages/softwareproperties/dbus/SoftwarePropertiesDBus.py", line 66, in __init__
11 self._livepatch_service = LivepatchService()
12 File "/lib/python3/dist-packages/softwareproperties/LivepatchService.py", line 96, in __init__
13 self._session = requests_unixsocket.Session()
14NameError: name 'requests_unixsocket' is not defined
重新安装sudo apt install --reinstall python3-urllib3再运行，这回日志显示chardet有问题：
1 import requests_unixsocket
2 File "/lib/python3/dist-packages/requests_unixsocket/__init__.py", line 1, in <module>
3 import requests
4 File "/lib/python3/dist-packages/requests/__init__.py", line 44, in <module>
5 import chardet
6ModuleNotFoundError: No module named 'chardet'
7Traceback (most recent call last):
8 File "/usr/lib/software-properties/software-properties-dbus", line 68, in <module>
9 server = SoftwarePropertiesDBus(bus, datadir=datadir)
10 File "/lib/python3/dist-packages/softwareproperties/dbus/SoftwarePropertiesDBus.py", line 66, in __init__
11 self._livepatch_service = LivepatchService()
12 File "/lib/python3/dist-packages/softwareproperties/LivepatchService.py", line 96, in __init__
13 self._session = requests_unixsocket.Session()
14NameError: name 'requests_unixsocket' is not defined
继续sudo apt install --reinstall python3-chardet，再执行终于看到了期待依旧的窗口：
最后，简要总结一下这个问题解决的两个关键点：
- 通过搜索了解到：
software-properties-gtk启动失败是由于python包有问题 - 通过修改源码，打印
import导致的异常，找到有问题的python包
最后的最后：
try-except没事别吞异常，会导致程序无法运行的异常至少记条日志。