B.16. Unable to connect to server at 'host:16509': Connection refused ... error: failed to connect to the hypervisor

Symptom
While libvirtd should listen on TCP ports for connections, the connections fail: 
# virsh -c qemu+tcp://host/system
error: unable to connect to server at 'host:16509': Connection refused
error: failed to connect to the hypervisor
The libvirt daemon is not listening on TCP ports even after changing configuration in /etc/libvirt/libvirtd.conf: 
# grep listen_ /etc/libvirt/libvirtd.conf
listen_tls = 1
listen_tcp = 1
listen_addr = "0.0.0.0"
However, the TCP ports for libvirt are still not open after changing configuration: 
# netstat -lntp | grep libvirtd
#
Investigation
The libvirt daemon was started without the --listen option. Verify this by running this command: 
# ps aux | grep libvirtd
root     27314  0.0  0.0 1000920 18304 ?       Sl   Feb16   1:19 libvirtd --daemon
The output does not contain the --listen option.
Solution
Start the daemon with the --listen option.
To do this, modify the /etc/sysconfig/libvirtd file and uncomment the following line: 
#LIBVIRTD_ARGS="--listen"
Then restart the libvirtd service with this command: 
# /etc/init.d/libvirtd restart