Unmounting Virtualbox Guest Additions ISO from: /mnt


Under the new “Big Sur”, running “vagrant up” when vagrant-vbguest is installed (and used) causes an error whereby a mount is looked for and generates a condition where vagrant-vbguest will not run and fails hard. The error output is:

Unmounting Virtualbox Guest Additions ISO from: /mnt
umount: /mnt: not mounted.
==> default: Checking for guest additions in VM...
    default: No guest additions were detected on the base box for this VM! Guest
    default: additions are required for forwarded ports, shared folders, host only
    default: networking, and more. If SSH fails on this machine, please install
    default: the guest additions and repackage the box to continue.
    default: This is not an error message; everything may continue to work properly,
    default: in which case you may ignore this message.
The following SSH command responded with a non-zero exit status.
Vagrant assumes that this means the command failed!

umount /mnt

Stdout from the command:

Stderr from the command:

umount: /mnt: not mounted.


Method #1: Add config.vbguest.installer_options = { allow_kernel_upgrade: true } to your Vagrantfile to allow system up2date

Vagrant.configure("2") do |config|
  # The most common configuration options are documented and commented below.
  # For a complete reference, please see the online documentation at
  # https://docs.vagrantup.com.

  # Every Vagrant development environment requires a box. You can search for
  # boxes at https://vagrantcloud.com/search.
  config.vm.box = "centos/stream8"
  config.vbguest.installer_options = { allow_kernel_upgrade: true }

Method #2: fails under Vbguest 0.28.0. Downgrading to 0.21.0 solves the issue

vagrant plugin uninstall vagrant-vbguest
vagrant plugin install vagrant-vbguest --plugin-version 0.21


  • /var/www/html/lntn203/wiki/data/pages/devops-sysadmin/vagrant/vagrant-umount-mnt-not-mounted.txt
  • Last modified: 15 months ago
  • by nghiale@infotechviet.com