原因：因为突然断电，导致机器关闭
结果：发现有一台虚拟机无法启动，一直报错 Unmount and run xfs_repair
分析：主机异常掉电后里面的虚拟机无法启动，主要是损坏的分区
解决办法：
原因：看出来应该是dm-0分区损坏，修复就可以了
1：启动虚拟机E进入单用户模式
2：在linux16开头的哪一行后面添加rd.break，ctrl+x进入救援模式
3：分析dm-0
ls -l /dev/mapper
4:卸载目录
umount /dev/mapper/centos-root
5:修复目录
xfs_repair -L /dev/mapper/centos-root
6：重启机器
init 6修复完成
xfs_repair -h
xfs_repair: invalid option -- 'h'
Usage: xfs_repair [options] device
Options:
-f The device is a file
-L Force log zeroing. Do this as a last resort.
-l logdev Specifies the device where the external log resides.
-m maxmem Maximum amount of memory to be used in megabytes.
-n No modify mode, just checks the filesystem for damage.
-P Disables prefetching.
-r rtdev Specifies the device where the realtime section resides.
-v Verbose output.
-c subopts Change filesystem parameters - use xfs_admin.
-o subopts Override default behaviour, refer to man page.
-t interval Reporting interval in minutes.
-d Repair dangerously.
-V Reports version and exits.