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

Running vagrant destroy sometimes fails with:

VBoxManage: error: Cannot unregister the machine 'CnC_default_1643660523119_45689' while it is locked

The VM is locked because a VirtualBox process is still holding onto it. Kill the headless process and try again:

killall -9 VBoxHeadless && vagrant destroy

killall -9 VBoxHeadless force-kills any running VirtualBox headless instances. The && runs vagrant destroy only if that succeeds.