i‘m new to use vagrant，今天升级了下vbox里的ubuntu12.04内核，结果vagrant reload后出现报错。
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
The error output from the last command was:
stdin: is not a tty
/sbin/mount.vboxsf: mounting failed with the error: No such device
vagrant ssh登陆后发现共享文件夹没了，无奈Google之，之后找到两种方法。
1,sudo /etc/init.d/vboxadd setup
2,sudo apt-get install virtualbox-guest-utils
vagrant reload后问题完美解决。
vagrant故障记--升级虚拟机linux内核导致无法挂载共享文件夹
原文：http://my.oschina.net/u/148605/blog/385049