kvm virtual manager connection failed

I had the same problem in CentOS 7. In my case upgrading device-mapper-libs solved the issue:

yum upgrade device-mapper-libs

In my case, some hints were given by checking status of libvirtd:

service libvirtd status

There were errors like below, so if you have similar problem, upgrading device-mapper-libs should help.

Oct 18 17:55:34 localhost.localdomain libvirtd[6130]: failed to load
module /usr/lib64/libvirt/connection-driver/libvirt_driver_storage.so
/usr/lib64/libvirt/connection-driver/libvirt_driver_storage.so: symbol
dm_task_...k time reference

Oct 18 17:55:34 localhost.localdomain libvirtd[6130]: failed to load 
module /usr/lib64/libvirt/connection-driver/libvirt_driver_qemu.so 
/usr/lib64/libvirt/connection-driver/libvirt_driver_qemu.so: undefined
symbol: virStorageFileCreate<br>

To have possibility to run virt-manager correctly on the same machine as you'd like to control it (locally), you'll need to install the following packages:

qemu-kvm qemu-img virt-manager libvirt libvirt-python python-virtinst libvirt-client virt-install virt-viewer

Re-check if they are all correctly installed on your server, or simply run the following statement:

# yum -y install qemu-kvm qemu-img virt-manager libvirt libvirt-python python-virtinst libvirt-client virt-install virt-viewer

If some of described packages are not installed on your system, they'll be installed (and packages that are existing will be skipped).

Also, the following systemd services should be enabled and running on the machine: libvirtd.service libvirtd.socket libvirt-guests.service

Good luck!