Resizing existing VM partition

Use vagrant-disksize plugin from https://github.com/sprotheroe/vagrant-disksize

Set required disk size

Inside Vagrantfile

Vagrant.configure('2') do |config|
  config.vm.box = 'ubuntu/xenial64'
  config.disksize.size = '100GB'
end

Start Vagrant

vagrant up

or just reload it (if it's already up) with:

vagrant reload

Enter partitioning tool

sudo fdisk /dev/sda3

1. Press p to check current partitions setup
2. Press d to delete last partition
3. Press n to create new partition
4. Press t to adjust filesystem to match previous settings
5. Press p and make sure that new setup looks similar to the base one (from step 1.)
6. Press w to save settings

You are suppose to see that message:

The partition table has been altered.
Calling ioctl() to re-read partition table.
Re-reading the partition table failed.: Device or resource busy

The kernel still uses the old table. The new table will be used at the next reboot or after you run partprobe(8) or kpartx(8).

Exit Vagrant

exit
exit

Restart Vagrant

vagrant reload

Enter Vagrant

vagrant ssh

Resize existing partition to span to new available space

sudo resize2fs /dev/sda3

Hopefully it's working now and you have much more free space!

Sources

https://askubuntu.com/a/116367/175659