VagrantでCentOS7をhttpd/mysql/php でとりあえず動かしてホストから繋ぐまで、と思ってたらrubyとか入れている（WIP） - Qiita

vagrant up Failed to mount folders in Linux guest. This is usually beacuse 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 apache | cut -d: -f3`,dmode=777,fmode=777 /vagrant /vagrant mount -t vboxsf -o uid=`id -u vagrant`,g

[takets]

centos7にしてapacheがうまく動かない場合はfirewalldを疑う。