服务器断电，重启虚拟机时，发现libvirtd服务起不来
[root@sz-CI ~]# service libvirtd status -l
Redirecting to /bin/systemctl status -l libvirtd.service
● libvirtd.service - Virtualization daemon
Loaded: loaded (/usr/lib/systemd/system/libvirtd.service; enabled; vendor preset: enabled)
Active: failed (Result: start-limit) since Wed 2017-03-01 11:12:24 CST; 2min 34s ago
Docs: man:libvirtd(8)
http://libvirt.org
Process: 7188 ExecStart=/usr/sbin/libvirtd $LIBVIRTD_ARGS (code=exited, status=6)
Main PID: 7188 (code=exited, status=6)
Mar 01 11:12:24 sz-CI systemd[1]: Failed to start Virtualization daemon.
Mar 01 11:12:24 sz-CI systemd[1]: Unit libvirtd.service entered failed state.
Mar 01 11:12:24 sz-CI systemd[1]: libvirtd.service failed.
Mar 01 11:12:24 sz-CI systemd[1]: libvirtd.service holdoff time over, scheduling restart.
Mar 01 11:12:24 sz-CI systemd[1]: start request repeated too quickly for libvirtd.service
Mar 01 11:12:24 sz-CI systemd[1]: Failed to start Virtualization daemon.
Mar 01 11:12:24 sz-CI systemd[1]: Unit libvirtd.service entered failed state.
Mar 01 11:12:24 sz-CI systemd[1]: libvirtd.service failed.
/var/log/messages 日志报错
Mar 1 14:35:27 localhost systemd: Starting Virtualization daemon...
Mar 1 14:35:27 localhost journal: libvirt version: 1.2.17, package: 13.el7_2.4 (CentOS BuildSystem <http://bugs.centos.org>, 2016-03-31-16:56:26, worker1.bsys.centos.org)
Mar 1 14:35:27 localhost journal: Module /usr/lib64/libvirt/connection-driver/libvirt_driver_lxc.so not accessible
Mar 1 14:35:27 localhost journal: Cannot read CA certificate '/etc/pki/CA/cacert.pem': No such file or directory
Mar 1 14:35:27 localhost systemd: libvirtd.service: main process exited, code=exited, status=6/NOTCONFIGURED
Mar 1 14:35:27 localhost systemd: Failed to start Virtualization daemon.
Mar 1 14:35:27 localhost systemd: Unit libvirtd.service entered failed state.
Mar 1 14:35:27 localhost systemd: libvirtd.service failed.
Mar 1 14:35:28 localhost systemd: libvirtd.service holdoff time over, scheduling restart.
Mar 1 14:35:28 localhost systemd: start request repeated too quickly for libvirtd.service
Mar 1 14:35:28 localhost systemd: Failed to start Virtualization daemon.
Mar 1 14:35:28 localhost systemd: Unit libvirtd.service entered failed state.
Mar 1 14:35:28 localhost systemd: libvirtd.service failed.
看起来像是缺少libvirt_driver_lxc.so这个库和/etc/pki/CA/cacert.pem 认证密钥。
网上找了些方法，说是更新一下包就可以
查看包版本：yum info device-mapper-libs
更新软件包：yum update device-mapper-libs
照做之后，还是起不来。
服务起不来，虚拟就不能用，先不管那么多，先直接 /usr/sbin/libvirtd -d手动试一下服务能不能用，结果能用，那就先起着给大家用先。然后再来找原因。
原因没找到，找到了个解决办法。
修改这个文件 /etc/libvirt/libvirtd.conf，去掉tls和tcp两行的注释，建立连接时走tcp通道
服务能起来了
多了个16509端口，正常libvirtd服务并没有端口listen。
还望路过的大神告知。。。