kvm启动报错与selinux的设置相关解决方法
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1.问题说明
由于kvm所在的机器启用了SELINUX，后来将之关闭，关闭之后，发现kvm的虚拟机无法启动，启动过程中的报错信息如下：
[root@ESRoller ~]# virsh start zabbix
error: Failed to start domain zabbix
error: unsupported configuration: Unable to find security driver for label selinux
libvirt中的日志也提示报错：
[root@ESRoller ~]# tail -f /var/log/libvirt/libvirtd.log
2016-06-20 09:54:41.724+0000: 2388: error : qemuRemoveCgroup:754 : internal error Unable to find cgroup for zabbix
2016-06-20 09:54:41.724+0000: 2388: warning : qemuProcessStop:4403 : Failed to remove cgroup for zabbix
2016-06-20 09:54:41.725+0000: 2388: error : qemuAutostartDomain:284 : Failed to autostart VM ‘zabbix‘: unsupported configuration: Unable to find security driver for label selinux
2016-06-20 09:54:41.734+0000: 2388: error : virSecurityManagerGenLabel:376 : unsupported configuration: Unable to find security driver for label selinux
2016-06-20 09:54:41.741+0000: 2388: error : qemuRemoveCgroup:754 : internal error Unable to find cgroup for roller
2016-06-20 09:54:41.741+0000: 2388: warning : qemuProcessStop:4403 : Failed to remove cgroup for roller
2016-06-20 09:54:41.742+0000: 2388: error : qemuAutostartDomain:284 : Failed to autostart VM ‘roller‘: unsupported configuration: Unable to find security driver for label selinux
2016-06-20 09:59:07.548+0000: 2378: error : virSecurityManagerGenLabel:376 : unsupported configuration: Unable to find security driver for label selinux
2016-06-20 09:59:07.561+0000: 2378: error : qemuRemoveCgroup:754 : internal error Unable to find cgroup for zabbix
2016-06-20 09:59:07.561+0000: 2378: warning : qemuProcessStop:4403 : Failed to remove cgroup for zabbix
2.造成原因
由于机器开机状态时，将SElinux的状态信息save在虚拟机中，导致SElinux关闭之后，虚拟找不到对应的label，从而导致vm启动失败。
3.解决方法
virsh edit domain_name查看虚拟机的配置文件中，是否有selinux标签的相关设置，如果有，则将其删除，再启动vm。如果没有，则可能已经保存在vm状态中，将原有的状态删除即可(对应路径/var/lib/libvirt/qemu/save)，如下：
[root@ESRoller ~]# virsh managedsave-remove zabbix
Removed managedsave image for domain zabbix
[root@ESRoller ~]# virsh start zabbix
Domain zabbix started
[root@ESRoller ~]# virsh list
Id Name State
----------------------------------------------------
4 zabbix running
如果配置配置文件中有selinux相关的配置，将其删除，期配置类似于：
<seclabel type=‘dynamic‘ model=‘selinux‘ relabel=‘yes‘>
<label>system_u:system_r:svirt_t:s0:c625,c859</label>
<imagelabel>system_u:object_r:svirt_image_t:s0:c625,c859</imagelabel>
</seclabel>
