CentOS无法启动，启动分区无法找到，然后就报了个堆栈信息：
ACPI: wmi: Mapper loaded
dracut Warning: No root device "block: /dev/sda4" found
dracut Warning: Boot has failed. To debug this issue add "rdshell" to the kernel command line.
dracut Warning: Signal caught!
dracut Warning: Boot has failed. To debug this issue add "rdshell" to the kernel command line.
kernel Panic - not syncing: Attempted to kill init!
Pid: 1, comm: init Tainted: G I-------2.6.32-358.el6.x86_64 #1
Call Trace:
[]? panic+0xa7/0x16f
[]? do_exit0x25/0x870
[]? fput_+0x25/0x30
[]? do_group_exit+0x58/0xd0
[]? sys_exit_group+0x17/0x20
[]? system_call_fastpath+0x16/x1b
Panic occurred, switching back to text console
*note1*: block device sought is not shown in /dev/fstab.
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ACPI:wmi:Mapperloaded
dracutWarning:Norootdevice"block: /dev/sda4"found
dracutWarning:Boothasfailed.Todebugthisissueadd"rdshell"tothekernelcommandline.
dracutWarning:Signalcaught!
dracutWarning:Boothasfailed.Todebugthisissueadd"rdshell"tothekernelcommandline.
kernelPanic-notsyncing:Attemptedtokillinit!
Pid:1,comm:initTainted:GI-------2.6.32-358.el6.x86_64#1
CallTrace:
[]?panic+0xa7/0x16f
[]?do_exit0x25/0x870
[]?fput_+0x25/0x30
[]?do_group_exit+0x58/0xd0
[]?sys_exit_group+0x17/0x20
[]?system_call_fastpath+0x16/x1b
Panicoccurred,switchingbacktotextconsole
*note1*:blockdevicesoughtisnotshownin/dev/fstab.
看样子是磁盘找不到了，想想前不久加了个磁盘装了其他的系统，会不会是影响了分区。
然后进去到另外的ubuntu系统，查看分区表：
发现分区全部挂在了sdb，然而实际上最开始装系统的时候磁盘应该是sda：
分析了一下分区信息，其中 sdb1-sdb7 应该就是我的CentOS分区了，50G的sdb4就是根分区，先把它挂载到当前系统。
ma@Y485:~$ sudo mkdir /sdb4
ma@Y485:~$ sudo mount /dev/sdb4 /sdb4/
ma@Y485:~$ cat /sdb4/etc/fstab
# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
#
# / was on /dev/sda12 during installation
UUID=8c9c0656-bd8a-41e0-8aae-43eaf8938227 / ext4 errors=remount-ro 0 1
UUID=6b60d3c1-221b-48de-9819-eb41cfbdc0cc /boot ext4 defaults 0 2
UUID=BAE5-8056 /boot/efi vfat umask=0077 0 1
UUID=122bd403-dd15-4616-a5ee-95b3fbeba590 /data ext4 defaults 0 2
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ma@Y485:~$sudomkdir/sdb4
ma@Y485:~$sudomount/dev/sdb4/sdb4/
ma@Y485:~$cat/sdb4/etc/fstab
# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
#
# / was on /dev/sda12 during installation
UUID=8c9c0656-bd8a-41e0-8aae-43eaf8938227/ext4errors=remount-ro01
UUID=6b60d3c1-221b-48de-9819-eb41cfbdc0cc/bootext4defaults02
UUID=BAE5-8056/boot/efivfatumask=007701
UUID=122bd403-dd15-4616-a5ee-95b3fbeba590/dataext4defaults02
发现所有的分区都是通过ID来标记的，因此基本定位到问题的原因为：添加新磁盘后，之前的磁盘变成了sdb分区，然而系统里面的磁盘ID还是指向开始的sda分区。就导致了分区找不到，系统无法启动。所以最后解决方法就是把所有的UUID都改成当前的分区号：
/dev/sdb4 / ext4 defaults 1 1
/dev/sdb2 /boot ext4 defaults 1 2
/dev/sdb1 /boot/efi vfat umask=0077,shortname=winnt 0 0
/dev/sdb6 /data ext4 defaults 1 2
/dev/sdb7 /home ext4 defaults 1 2
/dev/sdb5 /usr/local ext4 defaults 1 2
/dev/sdb3 swap swap defaults 0 0
...
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/dev/sdb4/ext4defaults11
/dev/sdb2/bootext4defaults12
/dev/sdb1/boot/efivfatumask=0077,shortname=winnt00
/dev/sdb6/dataext4defaults12
/dev/sdb7/homeext4defaults12
/dev/sdb5/usr/localext4defaults12
/dev/sdb3swapswapdefaults00
...
保存重启，然后就好了。
