今天部署了一套K版的OpenStack环境后，启动nova-compute后，日志里狂报如下错误（因为其内部有定时任务需要去连libvirtd进程）：
2015-08-14 10:01:00.061 28580 TRACE nova.virt.libvirt.host File "/usr/lib64/python2.7/site-packages/libvirt.py", line 105, in openAuth 2015-08-14 10:01:00.061 28580 TRACE nova.virt.libvirt.host if ret is None:raise libvirtError('virConnectOpenAuth() failed') 2015-08-14 10:01:00.061 28580 TRACE nova.virt.libvirt.host libvirtError: no connection driver available for qemu:///system
刚开始看到这个错误，首先第一反应是不是 libvirtd 进程没有启起来，于是 ps 查看确定下，发现已经启动起来了：
[root@localhost ~]# ps aux | grep libvirtd root 2648 0.0 0.0 112640 980 pts/1 S+ 10:34 0:00 grep --color=auto libvirtd root 31850 0.1 0.0 1053776 7264 ? Ssl 10:17 0:01 /usr/sbin/libvirtd --listen
后来，尝试直接执行下 virsh list 命令，同样得到如下错误：
[root@localhost ~]# virsh list error: failed to connect to the hypervisor error: no valid connection error: no connection driver available for <null> error: Failed to reconnect to the hypervisor
然后在想是不是URI不对，于是我指定URI再次尝试执行命令，同样返回错误：
[root@localhost ~]# virsh -c qemu:///system list error: failed to connect to the hypervisor error: no connection driver available for qemu:///system
为保持每次使用的URI都正确，后来我将 /etc/libvirt/libvirt.conf 配置文件里的 uri_default 直接设置为 qemu:///system：
[root@localhost ~]# cat /etc/libvirt/libvirt.conf # # This can be used to setup URI aliases for frequently # used connection URIs. Aliases may contain only the # characters a-Z, 0-9, _, -. # # Following the '=' may be any valid libvirt connection # URI, including arbitrary parameters #uri_aliases = [ # "hail=qemu+ssh://root@hail.cloud.example.com/system", # "sleet=qemu+ssh://root@sleet.cloud.example.com/system", #] # # This can be used to prevent probing of the hypervisor # driver when no URI is supplied by the application. uri_default = "qemu:///system"
然后重启 libvirtd 进程，通过 systemctl 命令查看下 libvirtd 进程的状态，发现有如下3个错误：
[root@localhost ~]# systemctl status libvirtd libvirtd.service - Virtualization daemon Loaded: loaded (/usr/lib/systemd/system/libvirtd.service; enabled) Active: active (running) since Fri 2015-08-14 10:11:13 CST; 4s ago Docs: man:libvirtd(8) http://libvirt.org Main PID: 30568 (libvirtd) CGroup: /system.slice/libvirtd.service └─30568 /usr/sbin/libvirtd --listen Aug 14 10:11:13 localhost.localdomain libvirtd[30568]: libvirt version: 1.2.8, package: 16.el7_1.3 (CentOS BuildSystem <http://bugs.centos.org>, 2015-05-12-20:12:58, worker1.bsys.centos.org) Aug 14 10:11:13 localhost.localdomain libvirtd[30568]: failed to load module /usr/lib64/libvirt/connection-driver/libvirt_driver_storage.so /usr/lib64/libvirt/connection-driver/...e reference Aug 14 10:11:13 localhost.localdomain libvirtd[30568]: failed to load module /usr/lib64/libvirt/connection-driver/libvirt_driver_qemu.so /usr/lib64/libvirt/connection-driver/lib...eFileCreate Aug 14 10:11:13 localhost.localdomain libvirtd[30568]: Module /usr/lib64/libvirt/connection-driver/libvirt_driver_lxc.so not accessible Aug 14 10:11:13 localhost.localdomain systemd[1]: Started Virtualization daemon. Hint: Some lines were ellipsized, use -l to show in full.
从上面错误来看，两个错误是由于libvirt_driver_storage.so、libvirt_driver_qemu.so加载失败，一个错误是由于没有libvirt_driver_lxc.so module。
于是查看下目录 /usr/lib64/libvirt/connection-driver/ 看看是否都有上面三个module：
[root@localhost ~]# ll /usr/lib64/libvirt/connection-driver/ total 1996 -rwxr-xr-x 1 root root 107440 May 13 04:16 libvirt_driver_interface.so -rwxr-xr-x 1 root root 148600 May 13 04:16 libvirt_driver_network.so -rwxr-xr-x 1 root root 107144 May 13 04:16 libvirt_driver_nodedev.so -rwxr-xr-x 1 root root 165688 May 13 04:16 libvirt_driver_nwfilter.so -rwxr-xr-x 1 root root 1175776 May 13 04:16 libvirt_driver_qemu.so -rwxr-xr-x 1 root root 86448 May 13 04:16 libvirt_driver_secret.so -rwxr-xr-x 1 root root 233448 May 13 04:16 libvirt_driver_storage.so
发现libvirt_driver_storage.so、libvirt_driver_qemu.so存在，而libvirt_driver_lxc.so确实不存在。
对于 libvirt_driver_lxc.so不存在 的情况，应该是相应的rpm包没有安装，我们只需要安装下即可：
[root@localhost ~]# yum install libvirt-daemon-lxc
安装完后，再次通过 systemctl 查看下 libvirtd 进程的状态，剩下两个错误还是没有得到解决：
[root@localhost ~]# systemctl status libvirtd libvirtd.service - Virtualization daemon Loaded: loaded (/usr/lib/systemd/system/libvirtd.service; enabled) Active: active (running) since Fri 2015-08-14 10:14:23 CST; 3s ago Docs: man:libvirtd(8) http://libvirt.org Main PID: 31204 (libvirtd) CGroup: /system.slice/libvirtd.service └─31204 /usr/sbin/libvirtd --listen Aug 14 10:14:22 localhost.localdomain libvirtd[31204]: libvirt version: 1.2.8, package: 16.el7_1.3 (CentOS BuildSystem <http://bugs.centos.org>, 2015-05-12-20:12:58, worker1.bsys.centos.org) Aug 14 10:14:22 localhost.localdomain libvirtd[31204]: failed to load module /usr/lib64/libvirt/connection-driver/libvirt_driver_storage.so /usr/lib64/libvirt/connection-driver/...e reference Aug 14 10:14:23 localhost.localdomain libvirtd[31204]: failed to load module /usr/lib64/libvirt/connection-driver/libvirt_driver_qemu.so /usr/lib64/libvirt/connection-driver/lib...eFileCreate Aug 14 10:14:23 localhost.localdomain systemd[1]: Started Virtualization daemon. Hint: Some lines were ellipsized, use -l to show in full.
于是查看 /var/log/message 关于libvirtd进程的系统日志，发现错误日志：
Aug 14 10:14:22 localhost journal: 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_get_info_with_deferred_remove, version Base not defined in file libdevmapper.so.1.02 with link time reference
Aug 14 10:14:23 localhost journal: 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
从上面错误来看，undefined symbol，很明显，是因为driver所需要的引用未定义，于是想应该是 libdevmapper.so.1.02 库太老，与 libvirtd 库不匹配，于是就尝试更新下 device-mapper：
[root@localhost ~]# yum update device-mapper
更新后，重启 libvirtd 进程，再次查看其状态：
[root@localhost ~]# systemctl restart libvirtd [root@localhost ~]# systemctl status libvirtd libvirtd.service - Virtualization daemon Loaded: loaded (/usr/lib/systemd/system/libvirtd.service; enabled) Active: active (running) since Fri 2015-08-14 10:17:20 CST; 2s ago Docs: man:libvirtd(8) http://libvirt.org Main PID: 31850 (libvirtd) CGroup: /system.slice/libvirtd.service └─31850 /usr/sbin/libvirtd --listen Aug 14 10:17:20 localhost.localdomain systemd[1]: Started Virtualization daemon.
发现没有问题出现了，尝试执行 virsh list 命令，也OK了：
[root@localhost ~]# virsh list
Id Name State
----------------------------------------------------
最后，启动openstack-nova-compute，也不再出现最初的错误了。