vagrant 启动报错是：mount: Protocol error 解决方法

Vagrant was unable to mount VirtualBox shared folders. This is usually
because the filesystem "vboxsf" is not available. This filesystem is
made available via the VirtualBox Guest Additions and kernel module.
Please verify that these guest additions are properly installed in the
guest. This is not a bug in Vagrant and is usually caused by a faulty
Vagrant box. For context, the command attempted was:


mount -t vboxsf -o uid=500,gid=500 vagrant /vagrant


The error output from the command was:
mount: Protocol error

1、检查自己的virtualbox 版本，选择相应的增强功能软件
可以在找到相应的版本的
2、挂载CDROM
登录系统
[root@lnmp3 ~]# mkdir /cdrom
[root@lnmp3 ~]# mount /dev/cdrom /cdrom
[root@lnmp3 ~]# cd /cdrom [root@lnmp3 cdrom]# ./VBoxLinuxAdditions.run
安装完成后：  
[root@lnmp3 cdrom]# rm -rf /sbin/mount.vboxsf
[root@lnmp3 cdrom]# ln -s /opt/VBoxGuestAdditions-X.X.XX/lib/VBoxGuestAdditions/mount.vboxsf /sbin/mount.vboxsf #X.X.XX就你的virtualbox 版本例如：5.1.20
3.运行：mount -t vboxsf -o uid=500,gid=500 vagrant /vagrant

 
ok!!!解决