how to increase disk space of virtual machine created by vagrant - vagrant

Question

I use vagrant create centos virtual machines using the following script:
Vagrant.configure("2") do |config|
(2..4).each do |i|
config.vm.define "node#{i}" do |node|
node.vm.provider "virtualbox" do |v|
v.name = "node#{i}"
v.memory = 3072
v.cpus = 2
config.disksize.size = '20GB'
end
node.vm.box = "cnode"
node.vm.hostname = "node#{i}"
node.vm.network :private_network, ip: "192.168.3.#{i}"
end
end
end
But / space is only 8.4GB:
[vagrant#node2 opt]$ df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/centos-root 8.4G 1.1G 7.4G 13% /
devtmpfs 1.4G 0 1.4G 0% /dev
tmpfs 1.4G 0 1.4G 0% /dev/shm
tmpfs 1.4G 8.3M 1.4G 1% /run
tmpfs 1.4G 0 1.4G 0% /sys/fs/cgroup
/dev/sda1 497M 118M 379M 24% /boot
none 234G 148G 87G 64% /vagrant

Answer 1

config.disksize.size is a parameter from the 3rd party https://github.com/sprotheroe/vagrant-disksize
As mentioned in the README :
Depending on the guest, you may need to resize the partition and the
filesystem from within the guest. At present the plugin only resizes
the underlying disk.
you can refer to vagrant no space left on device for the steps on the resizing partition