我正在使用 Ubuntu 16.04，并且使用以下命令禁用了全局菜单：
sudo apt-get remove indicator-appmenu
我怎样才能重新激活它？
我已经绑定了命令：
sudo apt-get install indicator-appmenu
但回应是：
Package indicator-appmenu is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Package 'indicator-appmenu' has no installation candidate