How to Resolve "Cannot Unregister the Machine While It Is Locked" Error in Vagrant

How to Resolve "Cannot Unregister the Machine While It Is Locked" Error in Vagrant

February 1, 2022

When working with Vagrant, a tool for building and managing virtual environments, you may encounter an error message that reads “Cannot unregister the machine while it is locked.” This is often accompanied by a block of error messages and command output, as shown below:

vagrant destroy
default: Are you sure you want to destroy the 'default' VM? [y/N] y
==> default: Destroying VM and associated drives…
There was an error while executing VBoxManage, a CLI used by Vagrant for controlling VirtualBox.
...
VBoxManage: error: Cannot unregister the machine 'CnC_default_1643660523119_45689' while it is locked
...

This error is usually thrown when attempting to destroy a Vagrant virtual machine (VM) using the vagrant destroy command. It signifies that the virtual machine is in a locked state, preventing it from being unregistered and deleted.

Solution #

The issue can be resolved by manually terminating any running instances of VirtualBox before running the vagrant destroy command again. The following command can be executed to kill all instances of VBoxHeadless, which is the process responsible for running virtual machines in headless mode:

killall -9 VBoxHeadless && vagrant destroy

This command will forcibly terminate any running VBoxHeadless processes and then execute the vagrant destroy command to remove the VM.

Understanding the Command #

Let’s break down what this command does:

  • killall -9 VBoxHeadless: The killall command sends a signal to terminate all processes with the specified name, in this case, VBoxHeadless. The -9 flag sends the SIGKILL signal, which forcefully kills the process.

  • &&: This is a shell operator that allows you to execute a second command only if the first command executes successfully.

  • vagrant destroy: This is the command to destroy the Vagrant virtual machine, which should now execute without any issues.

Conclusion #

Encountering errors while working with Vagrant can be frustrating, but understanding how to resolve them efficiently will save you time and effort. The “Cannot unregister the machine while it is locked” error can be easily fixed by using a combination of killall and vagrant destroy commands, enabling you to proceed with your development tasks smoothly.