VagrantでCentOS7を立てたが、httpアクセスが繋がらない時にやったこと ref: http://qiita.com/takuhou/items/1bdd8403a15be7411e20

app.js

app = require('express')();
app.get('/', function(req, res){
        res.send('hello world');
    });
app.listen(80);

file1.txt

config.vm.network "forwarded_port", guest: 80, host: 8080
config.vm.network "private_network", ip: "192.168.33.10", id:"http"

file2.txt

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:
/sbin/mount.vboxsf: mounting failed with the error: No such device

file3.txt

vagrant ssh

[vagrant@localhost ~]$ sudo /etc/init.d/vboxadd setup
Removing existing VirtualBox non-DKMS kernel modules       [  OK  ]
Building the VirtualBox Guest Additions kernel modules
Building the main Guest Additions module                   [  OK  ]
Building the shared folder support module                  [  OK  ]
Building the OpenGL support module                         [  OK  ]
Doing non-kernel setup of the Guest Additions              [  OK  ]
Starting the VirtualBox Guest Additions                    [  OK  ]

[vagrant@localhost ~]$ exit

vagrant halt
vagrant up