Vagrant 啓動報錯：the "vboxsf" file system is not available

有時候啓動vagrant的時候會出現如下錯誤：

default: Checking for guest additions in VM...
default: No guest additions were detected on the base box for this VM! Guest
default: additions are required for forwarded ports, shared folders, host only
default: networking, and more. If SSH fails on this machine, please install
default: the guest additions and repackage the box to continue.
default: This is not an error message; everything may continue to work properly,
default: in which case you may ignore this message.
default: Setting hostname...
default: Configuring and enabling network interfaces...
default: Mounting shared folders...
default: /vagrant => D:/opt/Vagrant/VWOS
Failed to mount folders in Linux guest. This is usually because
the "vboxsf" file system is not available. Please verify that
the guest additions are properly installed in the guest and
can work properly. The command attempted was:
mount -t vboxsf -o uid=`id -u vagrant`,gid=`getent group vagrant | cut -d: -f3` vagrant /vagrant
mount -t vboxsf -o uid=`id -u vagrant`,gid=`id -g vagrant` vagrant /vagrant

vagrant ssh登錄後發現共享文件夾沒了，須要在vagrant裏執行如下命令。

sudo /etc/init.d/vboxadd setup