vagrant upしたらエラーが起きた。

Failed to mount folders in Linux guest.

vboxsfが壊れているらしい。

vboxadd setupを再実行

ゲストOSで下記コマンドを実行する
エラーが起きていてもsshでログインしちゃってください。
$ vagrant ssh

[vagrant@vagrant-centos65 ~]$ sudo /etc/init.d/vboxadd setup

Removing existing VirtualBox non-DKMS kernel modules       [  OK  ]
Building the VirtualBox Guest Additions kernel modules
The headers for the current running kernel were not found. If the following
module compilation fails then this could be the reason.
The missing package can be probably installed with
yum install kernel-devel-2.6.32-431.3.1.el6.x86_64

Building the main Guest Additions module                   [FAILED]
(Look at /var/log/vboxadd-install.log to find out what went wrong)
Doing non-kernel setup of the Guest Additions              [  OK  ]

kernelをインストール(これは無くてもいいっぽい)

[vagrant@vagrant-centos65 ~]$ sudo yum install http://vault.centos.org/6.5/updates/x86_64/Packages/kernel-devel-2.6.32-431.3.1.el6.x86_64.rpm

[vagrant@vagrant-centos65 ~]$ sudo yum install gcc

再度setup

[vagrant@vagrant-centos65 ~]$ sudo /etc/init.d/vboxadd setup

ゲストOSをログアウトして、ホストOSで再起動

[vagrant@vagrant-centos65 ~]$ exit
$ vagrant halt
$ vagrant up