NFS mounts have been known to hang when running
vagrant up on Ubuntu. This is commonly caused by issues with using the
udp protocol for the NFS mount. In version 1.4.0+ of Vagrant, a new
nfs_udp option was added. I was able to add
nfs_udp: false to my
config.vm.synced_folder options to fix the issue.
config.vm.synced_folder "repositories", "/home/vagrant/repositories", type: "nfs", nfs_udp: false