virtualbox sharefolder mount fail

ubuntu 14.04.1 LTS 64bit

安装完GuestAdditions后，在终端输入

sudo mount -t vboxsf sharename /mnt/share

提示错误：
mount: wrong fs type, bad option, bad superblock on sharename,
       missing codepage or helper program, or other error
       (for several filesystems (e.g. nfs, cifs) you might
       need a /sbin/mount.<type> helper program)
       In some cases useful info is found in syslog - try
       dmesg | tail  or so

ll /sbin/mount.vboxsf

看到 mount.vboxsf 是一个符号链接，是红色

sudo find / -name mount.vboxsf

在下面位置找到

/opt/VBoxGuestAdditions-4.3.10/lib/VBoxGuestAdditions/mount.vboxsf*

在/sbin/ 下面重新建立符号链接，再次mount，成功