Used by Debian-like Linux distros, will get configured under guest's /var/cache/apt-cacher-ng and only works with NFS-shared folders since vboxsf is enforcing vagrant-user and apt-cacher is running under apt-cacher-ng user.

To manually enable it:

Vagrant.configure("2") do |config|
  config.vm.box = 'some-debian-box'
  config.cache.enable :apt_cacher

One use case for this bucket is if you are using containers inside your VMs, e.g VirtualBox -> LXC. This would allow you to reuse packages without sharing folder inside VirtualBox:

# install apt-cacher on (Host)-VM
$ sudo apt-get install apt-cacher-ng

# get the IP for eth0 interface
$ ifconfig eth0 |grep "inet addr"|awk '{print $2}' |cut -c6-20

# configure mirror on for your docker/LXC instances:
$ echo 'Acquire::http { Proxy "http://X.X.X.X:3142"; };' > /etc/apt/apt.conf.d/10mirror

# check, if working by tailing log on (Host)-VM, while installing packages on (Guest)-VMs
$ tail -f /var/log/apt-cacher-ng/apt-cacher.log