Last week I hit an odd issue with Vagrant. My environment was working fine when suddenly while resuming my box I started to get the following exception printed in the console:

INFO retryable: Retryable exception raised: #<Vagrant::Errors::LinuxNFSMountFailed: The following SSH command responded with a non-zero exit status.  
    Vagrant assumes that this means the command failed!

After checking VirtualBox I could see my virtual machine was running and I was able to open a shell connection to it, however, the NFS shares were not mounted.

That lead me to a path of trying to figure it out what could be the cause of the problem. In the end I didn't find a clear answer, the closest I got was this answer from Hashimoto: I understand that this is an intermittent issue for people. Iv'e even seen it myself. I'm still not sure what exactly causes this or how to get a solid reproduction. Or, how to fix it. Because of that, I'm going to close it since it is a rare issue. If someone can shed more light, I'd be happy to fix. Thanks.

What I did manage to do was gather a few steps that helped some people solved the Vagrant problems with NFS, they are listed below:

Before trying any of the options below make sure to export the VAGRANT_LOG=DEBUG environment variable to get more details in the console:

export VAGRANT_LOG=DEBUG  

1 - Configure firewall

On the mac, under System Preferences > Security & Privacy - Firewall
Make sure the Automatically allow signed software to receive incomming connections is checked

A more detailed firewall rule list can be found on this github issue

2 - Install vagrant VBGuest plugin

To install the plugin:

vagrant plugin install vagrant-vbguest  

The plugin's github page

3 - Restart vboxnet0 interface

Bring the interface down and up

$ sudo ifconfig vboxnet0 down
$ sudo ifconfig vboxnet0 up

4 - Restart NFSD daemon

First remove all the entries for your vagrant box in the /etc/exports file and then restart the nfsd daemon

sudo nfsd restart  

5 - Install NFS dependencies on the client

In the case of an Ubuntu virtual machine make sure the nfs-common and nfs-kernel-server are installed

apt-get install nfs-common nfs-kernel-server  

Sources