No guest machines are present

Symptom

No virtual machines are present although the daemon was successfuly started.

# virsh list --all
 Id    Name                           State
----------------------------------------------------
#

Solution

There are multiple possibilities what could have gone wrong:

# lsmod | grep kvm
kvm_intel             121346  0
kvm                   328927  1 kvm_intel
(kvm_amd on a AMD machine)
If the modules are not present insert them using the modprobe <modulename> command. (Note: KVM virtualization support may be compiled into the kernel, so modules are not needed. This is uncommon.)
# egrep "(vmx|svm)" /proc/cpuinfo
flags		: fpu vme de pse tsc ... svm ... skinit wdt npt lbrv svm_lock nrip_save
flags		: fpu vme de pse tsc ... svm ... skinit wdt npt lbrv svm_lock nrip_save
Enable virtualization extensions in your hardware's firmware configuration (BIOS setup).
# virsh uri
vbox:///system
There may be other hypervisors present and libvirt will talk to them by default.