Impossible to mount cdrom /dev/sr0 after boot from VagrantFile

[filoucrackeur94220]

Issue Description

With VirtualBox 7.0 and Vagrant, it seems impossible to associate an optical device from an .iso file without preventing the priority booting from the hard disk. Even when forcing the boot order, the virtual machine always boots from the attached ISO file instead of the present hard disk, causing issues during startup.

Configuration

Here is the configuration I am using in my Vagrantfile:

config.vm.disk :dvd, name: "trimbox-server.iso", file: ENV['ISO_PATH']

vb.customize ["modifyvm", :id, "--boot1", "disk"]
vb.customize ["modifyvm", :id, "--boot2", "none"]
vb.customize ["modifyvm", :id, "--boot3", "none"]
vb.customize ["modifyvm", :id, "--boot4", "none"]

Expected Behavior

I expected the virtual machine to boot from the hard disk when it is present, even if an ISO file is attached. In other words, I wanted the boot order to be respected, allowing for normal startup from the hard disk.

Actual Behavior

However, the virtual machine always boots from the attached ISO file when it is present, even after specifying the boot order. This prevents the operating system installed on the hard disk from booting correctly.

Reproduction Information

Vagrant Version

vagrant -v

Vagrant 2.4.1

Host Operating System

Fedora 41 with GNOME

Guest Operating System

Create a Vagrantfile using the configuration above.
Bring up the virtual machine with vagrant up.
Observe that the virtual machine boots from the ISO file instead of the hard disk.
Vagrantfile

Vagrant.configure("2") do |config|
  config.vm.box = "ubuntu/bionic64"

  # ISO configuration
  config.vm.disk :dvd, name: "test-server.iso", file: ENV['ISO_PATH']

  # Boot order configuration
  config.vm.provider "virtualbox" do |vb|
    vb.customize ["modifyvm", :id, "--boot1", "disk"]
    vb.customize ["modifyvm", :id, "--boot2", "none"]
    vb.customize ["modifyvm", :id, "--boot3", "none"]
    vb.customize ["modifyvm", :id, "--boot4", "none"]
  end
end

Debug Output

[taru-garg-hashicorp]

Hi @filoucrackeur94220,

Thank you for the detailed report. While attempting to debug the issue, I noticed a few interesting things, so below is what I discovered.

First, I mounted a non-bootable ISO (VBoxGuestAdditions_<Version>.iso) to the virtual machine, and it successfully mounted at /dev/sr0 without causing any issues during the boot process. Then, I attempted to mount a bootable ISO, which, as expected, resulted in failure because VirtualBox prioritized booting from it. After reviewing a few tickets on the VirtualBox forum—such as this one: ticket 19364—it appears that the boot order is not respected when EFI boot is enabled. To disable EFI boot, I added the command below to the Vagrantfile:

config.vm.provider 'virtualbox' do |vb|
    vb.customize ['modifyvm', :id, '--firmware', 'bios']
    # Boot order configuration ...
end

However, even after disabling EFI boot, I observed that for a bootable ISO like an OS installer, VirtualBox will load it regardless of the settings i.e even though when it is not selected in the boot order table. Although I didn’t find any official documentation on this behaviour, rather basing this on my debugging.

Finally, I tested the following configuration, here test-server.iso is a bootable iso:

Vagrant.configure('2') do |config|
  config.vm.box = 'bento/ubuntu-24.04'
  config.vm.disk :dvd, name: 'test-server.iso', file: 'test-server.iso' if ENV['ATTACH_ISO']

  config.vm.provider 'virtualbox' do |vb|
    vb.customize ['modifyvm', :id, '--firmware', 'bios']
    vb.customize ['modifyvm', :id, '--boot1', 'disk']
    vb.customize ['modifyvm', :id, '--boot2', 'none']
    vb.customize ['modifyvm', :id, '--boot3', 'none']
    vb.customize ['modifyvm', :id, '--boot4', 'none']
  end
end

To test this, run vagrant up using the above Vagrantfile, and once the machine has been provisioned, execute ATTACH_ISO=1 vagrant reload to attach the ISO.

For the specific issue you are facing, I would suggest it might help if you check:

1. Is the ISO being attached to the machine a bootable iso ?
2. Does it work once the EFI boot is disabled and the legacy bios boot is used ? ( i.e. Without having ATTACH_ISO env variable dependency, but just the line disabling EFI boot )
3. Finally, in case above doesn't work, does it work attaching the ISO post the machine is created and provisioned ?

Let me know if this helps!

Cheers!