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如何挂载一个镜像文件(how to mount an image file)

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如何挂载一个镜像文件(how to mount an image file)

08/16/2012master 4 Comments

在使用KVM或Xen虚拟化的情况下，经常需要使用镜像文件（image file），我们可以将Guest系统启动起来，然后对镜像文件进行修改，不过这样有时也是比较麻烦，其实也是可以将镜像文件直接进行mount的，可以用如下两种办法。
（本文写的RAW格式镜像文件的挂载；我的另一篇文章写了“如何挂载qcow2格式的镜像文件”）

方法一：找出分区开始的开始位置，使用mount命令的offset参数偏移掉前面不需要的，即可得到真正的分区。其具体步骤如下：
1. 用“fdisk -lu my.img”查询image信息；
2. 计算image内分区开始的地方（计算offset），用从N号sector（扇区）开始，则offset=N*M （M为一个sector的大小，一般为512）
3. 使用mount命令挂载为loop设备即可。 （如LVM分区，则会较复杂，请见本文最后的介绍）
在Linux系统上具体操作演示如下：

[root@jay-linux image]# fdisk -lu rhel6u2.img
You must set cylinders.
You can do this from the extra functions menu.

Disk rhel6u2.img: 0 MB, 0 bytes
255 heads, 63 sectors/track, 0 cylinders, total 0 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00048b34

Device Boot Start End Blocks Id System
rhel6u2.img1 * 2048 1026047 512000 83 Linux
Partition 1 does not end on cylinder boundary.
rhel6u2.img2 1026048 104857599 51915776 8e Linux LVM
Partition 2 has different physical/logical endings:
phys=(1023, 254, 63) logical=(6527, 21, 22)
[root@jay-linux image]# echo $((2048*512))
1048576
[root@jay-linux image]# mount -o loop,offset=1048576 rhel6u2.img /media/
[root@jay-linux image]# cd /media/
[root@jay-linux media]# ls
config-2.6.32-220.el6.x86_64 initramfs-3.5.0.img System.map-2.6.32-279.el6.x86_64
config-2.6.32-279.el6.x86_64 lost+found System.map-3.5.0
efi symvers-2.6.32-220.el6.x86_64.gz vmlinuz
grub symvers-2.6.32-279.el6.x86_64.gz vmlinuz-2.6.32-220.el6.x86_64
initramfs-2.6.32-220.el6.x86_64.img System.map vmlinuz-2.6.32-279.el6.x86_64
initramfs-2.6.32-279.el6.x86_64.img System.map-2.6.32-220.el6.x86_64 vmlinuz-3.5.0
[root@jay-linux media]# echo $((1026048*512))
525336576
[root@jay-linux media]# umount /media
[root@jay-linux media]# cd /home/image/
[root@jay-linux image]# umount /media
[root@jay-linux image]# mount -o loop,offset=525336576 rhel6u2.img /media/
mount: unknown filesystem type 'LVM2_member'
（镜像文件中的LVM分区mount的问题，本文最后单独说明）

[root@jay-linux image]# fdisk -lu sles11sp2-i386.img
You must set cylinders.
You can do this from the extra functions menu.

Disk sles11sp2-i386.img: 0 MB, 0 bytes
255 heads, 63 sectors/track, 0 cylinders, total 0 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x0002d3be

Device Boot Start End Blocks Id System
sles11sp2-i386.img1 2048 4208639 2103296 82 Linux swap / Solaris
Partition 1 does not end on cylinder boundary.
sles11sp2-i386.img2 * 4208640 41943039 18867200 83 Linux
Partition 2 has different physical/logical endings:
phys=(1023, 254, 63) logical=(2610, 212, 34)
[root@jay-linux image]# echo $((4208640*512))
2154823680
[root@jay-linux image]# mount -o loop,offset=2154823680 sles11sp2-i386.img /media
[root@jay-linux image]# cd /media/
[root@jay-linux media]# ls
bin dev home lost+found mnt proc sbin srv sys usr
boot etc lib media opt root selinux success tmp var
[root@jay-linux image]# umount /media/

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[root@jay-linux image]# fdisk -lu rhel6u2.img
You must set cylinders.
You can do this from the extra functions menu.
 
Disk rhel6u2.img: 0 MB, 0 bytes
255 heads, 63 sectors/track, 0 cylinders, total 0 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00048b34
 
      Device Boot      Start         End      Blocks   Id  System
rhel6u2.img1   *        2048     1026047      512000   83  Linux
Partition 1 does not end on cylinder boundary.
rhel6u2.img2         1026048   104857599    51915776   8e  Linux LVM
Partition 2 has different physical/logical endings:
     phys=(1023, 254, 63) logical=(6527, 21, 22)
[root@jay-linux image]# echo $((2048*512))
1048576
[root@jay-linux image]# mount -o loop,offset=1048576 rhel6u2.img /media/
[root@jay-linux image]# cd /media/
[root@jay-linux media]# ls
config-2.6.32-220.el6.x86_64         initramfs-3.5.0.img               System.map-2.6.32-279.el6.x86_64
config-2.6.32-279.el6.x86_64         lost+found                        System.map-3.5.0
efi                                  symvers-2.6.32-220.el6.x86_64.gz  vmlinuz
grub                                 symvers-2.6.32-279.el6.x86_64.gz  vmlinuz-2.6.32-220.el6.x86_64
initramfs-2.6.32-220.el6.x86_64.img  System.map                        vmlinuz-2.6.32-279.el6.x86_64
initramfs-2.6.32-279.el6.x86_64.img  System.map-2.6.32-220.el6.x86_64  vmlinuz-3.5.0
[root@jay-linux media]# echo $((1026048*512))
525336576
[root@jay-linux media]# umount /media
[root@jay-linux media]# cd /home/image/
[root@jay-linux image]# umount /media
[root@jay-linux image]# mount -o loop,offset=525336576 rhel6u2.img /media/
mount: unknown filesystem type 'LVM2_member'
（镜像文件中的LVM分区mount的问题，本文最后单独说明）
 
 
[root@jay-linux image]# fdisk -lu sles11sp2-i386.img
You must set cylinders.
You can do this from the extra functions menu.
 
Disk sles11sp2-i386.img: 0 MB, 0 bytes
255 heads, 63 sectors/track, 0 cylinders, total 0 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x0002d3be
 
             Device Boot      Start         End      Blocks   Id  System
sles11sp2-i386.img1            2048     4208639     2103296   82  Linux swap / Solaris
Partition 1 does not end on cylinder boundary.
sles11sp2-i386.img2   *     4208640    41943039    18867200   83  Linux
Partition 2 has different physical/logical endings:
     phys=(1023, 254, 63) logical=(2610, 212, 34)
[root@jay-linux image]# echo $((4208640*512))
2154823680
[root@jay-linux image]# mount -o loop,offset=2154823680 sles11sp2-i386.img /media
[root@jay-linux image]# cd /media/
[root@jay-linux media]# ls
bin   dev  home  lost+found  mnt  proc  sbin     srv      sys  usr
boot  etc  lib   media       opt  root  selinux  success  tmp  var
[root@jay-linux image]# umount /media/

方法二：用kpartx建立分区映射后，再mount映射后的设备即可，操作实例如下：

[root@jay-linux image]# kpartx -av sles11sp2-i386.img
add map loop3p1 (253:2): 0 4206592 linear /dev/loop3 2048
add map loop3p2 (253:3): 0 37734400 linear /dev/loop3 4208640

[root@jay-linux image]# mount /dev/mapper/loop3p2 /media/

[root@jay-linux image]# ls /media/
bin dev home lost+found mnt proc sbin srv sys usr
boot etc lib media opt root selinux success tmp var
[root@jay-linux image]# umount /media/
[root@jay-linux image]# mount /dev/mapper/loop3p1 /media/
/dev/mapper/loop3p1 looks like swapspace - not mounted
mount: you must specify the filesystem type
（其中的交换分区，我也还不知道是否可以mount；其实mount交换分区也没意义）

（使用完成后，卸载挂载点、删除映射关系即可）
[root@jay-linux image]# umount /media/
[root@jay-linux image]# kpartx -d sles11sp2-i386.img
loop deleted : /dev/loop3

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[root@jay-linux image]# kpartx -av sles11sp2-i386.img
add map loop3p1 (253:2): 0 4206592 linear /dev/loop3 2048
add map loop3p2 (253:3): 0 37734400 linear /dev/loop3 4208640
 
[root@jay-linux image]# mount /dev/mapper/loop3p2 /media/
 
[root@jay-linux image]# ls /media/
bin   dev  home  lost+found  mnt  proc  sbin     srv      sys  usr
boot  etc  lib   media       opt  root  selinux  success  tmp  var
[root@jay-linux image]# umount /media/
[root@jay-linux image]# mount /dev/mapper/loop3p1 /media/
/dev/mapper/loop3p1 looks like swapspace - not mounted
mount: you must specify the filesystem type
（其中的交换分区，我也还不知道是否可以mount；其实mount交换分区也没意义）
 
（使用完成后，卸载挂载点、删除映射关系即可）
[root@jay-linux image]# umount /media/
[root@jay-linux image]# kpartx -d sles11sp2-i386.img
loop deleted : /dev/loop3

关于LVM的mount，可以参考文末参考资料中的vpsee的文章（我也是试多次没做成功，才偶然看到这篇文章的），我对镜像文件中LVM分区的mount操作如下供参考。

[root@jay-linux image]# fdisk -lu rhel6u2.img
You must set cylinders.
You can do this from the extra functions menu.

Disk rhel6u2.img: 0 MB, 0 bytes
255 heads, 63 sectors/track, 0 cylinders, total 0 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00048b34

Device Boot Start End Blocks Id System
rhel6u2.img1 * 2048 1026047 512000 83 Linux
Partition 1 does not end on cylinder boundary.
rhel6u2.img2 1026048 104857599 51915776 8e Linux LVM
Partition 2 has different physical/logical endings:
phys=(1023, 254, 63) logical=(6527, 21, 22)
[root@jay-linux image]# echo $((1026048*512))
525336576
[root@jay-linux image]# losetup /dev/loop0 rhel6u2.img -o 525336576
[root@jay-linux image]# pvscan
PV /dev/loop0 VG VolGroup lvm2 [49.51 GiB / 0 free]
Total: 1 [49.51 GiB] / in use: 1 [49.51 GiB] / in no VG: 0 [0 ]
[root@jay-linux image]# vgchange -ay VolGroup
2 logical volume(s) in volume group "VolGroup" now active
[root@jay-linux image]# lvs
LV VG Attr LSize Pool Origin Data% Move Log Copy% Convert
lv_root VolGroup -wi-a--- 45.57g
lv_swap VolGroup -wi-a--- 3.94g
[root@jay-linux image]# mount /dev/VolGroup/lv_root /media/
[root@jay-linux image]# ls /media/
bin cgroup etc lib lost+found misc net proc sbin srv tmp var
boot dev home lib64 media mnt opt root selinux sys usr

（使用完后的卸载操作，如下）
[root@jay-linux image]# umount /media/
[root@jay-linux image]# vgchange -an VolGroup
0 logical volume(s) in volume group "VolGroup" now active
[root@jay-linux image]# losetup -d /dev/loop0

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[root@jay-linux image]# fdisk -lu rhel6u2.img
You must set cylinders.
You can do this from the extra functions menu.
 
Disk rhel6u2.img: 0 MB, 0 bytes
255 heads, 63 sectors/track, 0 cylinders, total 0 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00048b34
 
      Device Boot      Start         End      Blocks   Id  System
rhel6u2.img1   *        2048     1026047      512000   83  Linux
Partition 1 does not end on cylinder boundary.
rhel6u2.img2         1026048   104857599    51915776   8e  Linux LVM
Partition 2 has different physical/logical endings:
     phys=(1023, 254, 63) logical=(6527, 21, 22)
[root@jay-linux image]# echo $((1026048*512))
525336576
[root@jay-linux image]# losetup /dev/loop0 rhel6u2.img -o 525336576
[root@jay-linux image]# pvscan
  PV /dev/loop0   VG VolGroup   lvm2 [49.51 GiB / 0    free]
  Total: 1 [49.51 GiB] / in use: 1 [49.51 GiB] / in no VG: 0 [0   ]
[root@jay-linux image]# vgchange -ay VolGroup
  2 logical volume(s) in volume group "VolGroup" now active
[root@jay-linux image]# lvs
  LV      VG       Attr     LSize  Pool Origin Data%  Move Log Copy%  Convert
  lv_root VolGroup -wi-a--- 45.57g
  lv_swap VolGroup -wi-a---  3.94g
[root@jay-linux image]# mount /dev/VolGroup/lv_root /media/
[root@jay-linux image]# ls /media/
bin   cgroup  etc   lib    lost+found  misc  net  proc  sbin     srv  tmp  var
boot  dev     home  lib64  media       mnt   opt  root  selinux  sys  usr
 
（使用完后的卸载操作，如下）
[root@jay-linux image]# umount /media/
[root@jay-linux image]# vgchange -an VolGroup
  0 logical volume(s) in volume group "VolGroup" now active
[root@jay-linux image]# losetup -d /dev/loop0

mount LVM 分区的 参考资料：

Related posts:

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  4. “mount: could not find any free loop device”解决方案