我重新安装了 mate 桌面环境，但问题仍然存在。没有面板，没有菜单。热键响应灵敏，GUI 应用程序加载无问题。
dconf 编辑器毫无怨言地浏览面板。
有这个：
mate-panel --reset
mate-panel: symbol lookup error: mate-panel: undefined symbol: matemenu_tree_unref
以下是日志中的一段话：
WARNING: Unable to find provider 'mate-panel' of required component 'panel'
对于 N0rbert
apt-cache policy mate-panel python-mate-menu libmate-menu2
mate-panel:
Installed: 1.20.1-3ubuntu1
Candidate: 1.20.1-3ubuntu1
Version table:
*** 1.20.1-3ubuntu1 500
500 http://ca.archive.ubuntu.com/ubuntu bionic/universe amd64 Packages
100 /var/lib/dpkg/status
python-mate-menu:
Installed: 1.20.0-2
Candidate: 1.20.0-2
Version table:
*** 1.20.0-2 500
500 http://ca.archive.ubuntu.com/ubuntu bionic/universe amd64 Packages
100 /var/lib/dpkg/status
libmate-menu2:
Installed: 1.20.0-2
Candidate: 1.20.0-2
Version table:
*** 1.20.0-2 500
500 http://ca.archive.ubuntu.com/ubuntu bionic/universe amd64 Packages
100 /var/lib/dpkg/status
重新安装引用的软件包后：
mate-panel --replace
mate-panel: symbol lookup error: mate-panel: undefined symbol matemenu_tree_unref
cat .xsession-errors
在发出替换命令之前，我已经存档并清空了 .xsession-errors。执行 --replace 之后，文件为空。
N0rbert 询问这是 Python 问题吗？请注意，我们已安装 mate-menu，不会卸载
pip uninstall mate-menu
Not uninstalling mate-menu at /usr/lib/python2.7/dist-packages, outside
environment /usr
pip list
asn1crypto (0.24.0)
autokey (0.90.4)
backports.functools-lru-cache (1.5)
cajarename (17.3.28)
configobj (5.0.6)
cryptography (2.1.4)
cycler (0.10.0)
duplicity (0.7.17)
enum34 (1.1.6)
fasteners (0.12.0)
folder-color-common (0.0.86)
funcsigs (1.0.2)
idna (2.6)
ipaddress (1.0.17)
keyring (10.6.0)
keyrings.alt (3.0)
kiwisolver (1.0.1)
lockfile (0.12.2)
mate-menu (18.4.3)
mock (2.0.0)
monotonic (1.0)
pbr (3.1.1)
pip (9.0.1)
pycairo (1.16.2)
pycrypto (2.6.1)
pygobject (3.26.1)
pyinotify (0.9.6)
pyparsing (2.2.0)
python-dateutil (2.7.2)
python-xlib (0.20)
pytz (2018.4)
pyxdg (0.25)
SecretStorage (2.3.1)
setproctitle (1.1.10)
setuptools (39.0.1)
simplejson (3.13.2)
six (1.11.0)
subprocess32 (3.2.7)
wheel (0.30.0)
X-Tile (2.5.1)