1.  VBoxManage createvm --name $VM --ostype "Ubuntu_64" --register
2.  VBoxManage createhd --filename $VM.vdi --size 10000
3.  mv ubuntu-server.vdi ubuntu-server/
4.  VBoxManage storagectl $VM --name "IDE Controller" --add ide
5.  VBoxManage storageattach $VM --storagectl "IDE Controller" --port 0 --device 0 --type hdd --medium $VM.vdi
6.  VBoxManage storageattach $VM --storagectl "IDE Controller" --port 1 --device 0 --type dvddrive --medium ~/Downloads/ubuntu-16.04.2-desktop-amd64.iso
7.  VBoxManage modifyvm $VM --ioapic on
8.  VBoxManage modifyvm $VM --boot1 dvd --boot2 disk --boot3 none --boot4 none
9.  VBoxManage modifyvm $VM --memory 1024 --vram 128
10. VBoxManage modifyvm $VM --nic1 bridged --bridgeadapter1 eth0
11. VBoxHeadless --startvm $VM &

ERROR:

Oracle VM VirtualBox Headless Interface 5.0.40_Ubuntu
(C) 2008-2017 Oracle Corporation
All rights reserved.

Error: failed to start machine. Error message: Could not open the medium '/home/bipul/VirtualBox VMs/ubuntu-server.vdi'.
VD: error VERR_FILE_NOT_FOUND opening image file '/home/bipul/VirtualBox VMs/ubuntu-server.vdi' (VERR_FILE_NOT_FOUND)