xen无法正常启动，无法mount，如何进入单用户模式？

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XEN VPS domU 无法正常启动，无法mount的备份方法：

现象：
EFI Variables Facility v0.08 2004-May-17
usbcore: registered new interface driver hiddev
usbcore: registered new interface driver usbhid
usbhid: v2.6:USB HID core driver
TCP cubic registered
Initializing XFRM netlink socket
NET: Registered protocol family 17
registered taskstats version 1
XENBUS: Device with no driver: device/vbd/51713
XENBUS: Device with no driver: device/vbd/51714
XENBUS: Device with no driver: device/vif/0
XENBUS: Device with no driver: device/console/0
drivers/rtc/hctosys.c: unable to open rtc device (rtc0)
Initalizing network drop monitor service
Freeing unused kernel memory: 1264k freed
Write protecting the kernel read-only data: 10240k
Freeing unused kernel memory: 900k freed
Freeing unused kernel memory: 1672k freed
dracut: dracut-004-303.el6
udev: starting version 147
dracut: Starting plymouth daemon
xlblk_init: register_blkdev major: 202
blkfront: xvda1: barriers disabled
blkfront: xvda2: barriers disabled
kjournald starting.  Commit interval 5 seconds
EXT3-fs (xvda1): mounted filesystem with ordered data mode
dracut: Remounting /dev/xvda1 with -o errors=remount-ro,usrjquota=quota.user,jqfmt=vfsv0,ro
kjournald starting.  Commit interval 5 seconds
EXT3-fs (xvda1): mounted filesystem with ordered data mode
dracut: Mounted root filesystem /dev/xvda1
SELinux:  Disabled at runtime.
type=1404 audit(1413384193.486:2): selinux=0 auid=4294967295 ses=4294967295
dracut:
dracut: Switching root
udev: starting version 147
Initialising Xen virtual ethernet driver.
device-mapper: uevent: version 1.0.3
device-mapper: ioctl: 4.23.6-ioctl (2012-07-25) initialised: [email protected]
EXT3-fs (xvda1): using internal journal
Adding 8388600k swap on /dev/xvda2.  Priority:-1 extents:1 across:8388600k SS
到这里就卡住了，无法继续正常启动
在dom0尝试将此domU的image文件mount，也失败。怀疑是vps的硬盘损坏。

在solusvm设置custom config 增加extra="-s" 重启进入单用户模式
| How do I boot a domU single-user? Set extra="-s" in the guest config file.

然后再dom0进入console，用ls，df -h 等命令都能正常显示，并不像硬盘损坏非常严重的情况，service network start 和 service sshd restart 发现机器就可以ssh登录了，这时候，赶紧备份吧。因为怀疑是硬盘故障，备份的时候，尽量不要执行写入IO的操作，如 tar，gz等命令，而改为直接ftp或sftp上传备份，减少io操作。