服务器版本：CentOS Linux release 7.4
Linux lb 3.10.0-693.el7.x86_64 #1 SMP Tue Aug 22 21:09:27 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux
参考：https://www.cnblogs.com/yogurtwu/p/9988974.html
注：在翻了很多baidu和google相关文章后，逐步排查，根据手动执行libvirtd命令出现的报错信息才查到解决方法。一路坑。
对装有kvm虚拟机的服务器执行了安装libguestfs-tools后，发现出现了故障。
执行virsh list命令后会报以下错误：
virsh list
error: failed to connect to the hypervisor
error: Failed to connect socket to '/var/run/libvirt/libvirt-sock': No such file or directory
执行systemctl status libvirtd后报错：
● libvirtd.service - Virtualization daemon
Loaded: loaded (/usr/lib/systemd/system/libvirtd.service; enabled; vendor preset: enabled)
Active: failed (Result: start-limit) since Tue 2019-03-19 16:44:52 CST; 49min ago
Docs: man:libvirtd(8)
https://libvirt.org
Process: 21280 ExecStart=/usr/sbin/libvirtd $LIBVIRTD_ARGS (code=exited, status=3)
Main PID: 21280 (code=exited, status=3)
Tasks: 2 (limit: 32768)
CGroup: /system.slice/libvirtd.service
├─1007 /usr/sbin/dnsmasq --conf-file=/var/lib/libvirt/dnsmasq/default.conf --leasefile-ro --dhcp-script=/usr/libexec/libvirt_leaseshelper
└─1008 /usr/sbin/dnsmasq --conf-file=/var/lib/libvirt/dnsmasq/default.conf --leasefile-ro --dhcp-script=/usr/libexec/libvirt_leaseshelper
Mar 19 16:44:52 develop systemd[1]: Failed to start Virtualization daemon.
Mar 19 16:44:52 develop systemd[1]: Unit libvirtd.service entered failed state.
Mar 19 16:44:52 develop systemd[1]: libvirtd.service failed.
Mar 19 16:44:52 develop systemd[1]: libvirtd.service holdoff time over, scheduling restart.
Mar 19 16:44:52 develop systemd[1]: Stopped Virtualization daemon.
Mar 19 16:44:52 develop systemd[1]: start request repeated too quickly for libvirtd.service
Mar 19 16:44:52 develop systemd[1]: Failed to start Virtualization daemon.
Mar 19 16:44:52 develop systemd[1]: Unit libvirtd.service entered failed state.
Mar 19 16:44:52 develop systemd[1]: libvirtd.service failed.
执行systemctl restart libvirtd后报错：
Job for libvirtd.service failed because start of the service was attempted too often. See "systemctl status libvirtd.service" and "journalctl -xe" for details.
To force a start use "systemctl reset-failed libvirtd.service" followed by "systemctl start libvirtd.service" again.
原因：
因为依赖安装了某些包（比如libguestfs-tools）后，跟着KVM相关的软件也跟着升级，但是CentOS7.4无法运行这个版本的libvirt，最简单粗暴的做法就是移除该模块，重启libvirtd。
解决办法：
mv /usr/lib64/libvirt/storage-backend/libvirt_storage_backend_rbd.so /usr/lib64/libvirt/storage-backend/libvirt_storage_backend_rbd.so-bak
systemctl restart libvirtd
再次执行virsh list，正常了：
