Ubuntu 软件中心从我的 Ubuntu 中消失，并且未显示在启动器中。当我sudo software-center在终端中运行时，输出如下：
2016-01-29 17:46:53,262 - softwarecenter.ui.gtk3.app - ERROR - could not initiate dbus
Traceback (most recent call last):
File "/usr/share/software-center/softwarecenter/ui/gtk3/app.py", line 1250, in setup_dbus_or_bring_other_instance_to_front
bus = dbus.SessionBus()
File "/usr/lib/python2.7/dist-packages/dbus/_dbus.py", line 211, in __new__
mainloop=mainloop)
File "/usr/lib/python2.7/dist-packages/dbus/_dbus.py", line 100, in __new__
bus = BusConnection.__new__(subclass, bus_type, mainloop=mainloop)
File "/usr/lib/python2.7/dist-packages/dbus/bus.py", line 122, in __new__
bus = cls._new_for_bus(address_or_type, mainloop=mainloop)
DBusException: org.freedesktop.DBus.Error.NoReply: Did not receive a reply. Possible causes include: the remote application did not send a reply, the message bus security policy blocked the reply, the reply timeout expired, or the network connection was broken.
2016-01-29 17:46:53,332 - softwarecenter.ui.gtk3.app - INFO - setting up proxy 'None'
Traceback (most recent call last):
File "/usr/bin/software-center", line 130, in <module>
app = SoftwareCenterAppGtk3(options, args)
File "/usr/share/software-center/softwarecenter/ui/gtk3/app.py", line 338, in __init__
self.icons)
File "/usr/share/software-center/softwarecenter/ui/gtk3/session/appmanager.py", line 66, in __init__
self.oauth_token = helper.find_oauth_token_sync()
File "/usr/share/software-center/softwarecenter/backend/ubuntusso.py", line 140, in find_oauth_token_sync
sso = self. _get_login_backend_and_connect()
File "/usr/share/software-center/softwarecenter/backend/ubuntusso.py", line 132, in _get_login_backend_and_connect
_(SOFTWARE_CENTER_SSO_DESCRIPTION))
File "/usr/share/software-center/softwarecenter/backend/login.py", line 80, in get_login_backend
sso_class = LoginBackendDbusSSO(window_id, appname, help_text)
File "/usr/share/software-center/softwarecenter/backend/login_impl/login_sso.py", line 46, in __init__
self.bus = dbus.SessionBus()
File "/usr/lib/python2.7/dist-packages/dbus/_dbus.py", line 211, in __new__
mainloop=mainloop)
File "/usr/lib/python2.7/dist-packages/dbus/_dbus.py", line 100, in __new__
bus = BusConnection.__new__(subclass, bus_type, mainloop=mainloop)
File "/usr/lib/python2.7/dist-packages/dbus/bus.py", line 122, in __new__
bus = cls._new_for_bus(address_or_type, mainloop=mainloop)
dbus.exceptions.DBusException: org.freedesktop.DBus.Error.NoReply: Did not receive a reply. Possible causes include: the remote application did not send a reply, the message bus security policy blocked the reply, the reply timeout expired, or the network connection was broken.
我要怎么做才能恢复软件中心？