挂载img类型的操作系统文件镜像的方法

1. 先查看第一个空闲loop设备

sudo losetup -f

/dev/loop0

2. 使用上一步得到的设备名，第一次创建loop设备

sudo losetup /dev/loop0 archlinux-2008.06-core-i686.img

3. 查看信息

sudo fdisk -lu /dev/loop0
Disk /dev/loop0: 322 MB, 322469376 bytes
53 heads, 12 sectors/track, 990 cylinders, total 629823 sectors
Units = sectors of 1 * 512 = 512 bytes
Disk identifier: 0x00000000
Device Boot Start End Blocks Id System
/dev/loop0p1 * 63 629822 314880 83 Linux
Partition 1 has different physical/logical beginnings (non-Linux?):
phys=(0, 1, 1) logical=(0, 5, 4)
Partition 1 has different physical/logical endings:
phys=(39, 52, 12) logical=(990, 15, 3)

我们可以看到，该镜像只有一个分区(loop0p1)，从第63扇区开始(Start列)，每扇区512字节(Units = sectors of 1 * 512 = 512 bytes)，我们算出offset，下面mout命令会用到：

63*512=32256

4. mount

sudo losetup -o 32256 /dev/loop1 archlinux-2008.06-core-i686.img
sudo mount -o loop /dev/loop1 /mnt/
ls /mnt/
addons archlive.sqfs boot lost+found

事实上，fdisk可以直接查看img文件(虽然功能不全，下面会说到)，mount可以自动创建loop设备，所以上面步骤可以简化为：
I. 查看信息

sudo fdisk -lu archlinux-2008.06-core-i686.img
You must set cylinders.
You can do this from the extra functions menu.
Disk archlinux-2008.06-core-i686.img: 0 MB, 0 bytes
53 heads, 12 sectors/track, 0 cylinders, total 0 sectors
Units = sectors of 1 * 512 = 512 bytes
Disk identifier: 0x00000000
Device Boot Start End Blocks Id System
archlinux-2008.06-core-i686.img1 * 63 629822 314880 83 Linux
Partition 1 has different physical/logical beginnings (non-Linux?):
phys=(0, 1, 1) logical=(0, 5, 4)
Partition 1 has different physical/logical endings:
phys=(39, 52, 12) logical=(990, 15, 3)

第一行抱怨不能得到cylinders，原因是普通文件上没有实现ioctl操作，我们可以看到0 cylinders，但这对我们不重要，关键是我们依然可以得到第一个分区（archlinux-2008.06-core-i686.img1）的偏移值

II. 直接mount

sudo mount -o loop,offset=32256 archlinux-2008.06-core-i686.img /mnt/
ls /mnt/
addons archlive.sqfs boot lost+found

再来一个复杂点的：

$ /sbin/fdisk -lu disk.img
You must set cylinders.
You can do this from the extra functions menu.

Disk disk.img: 0 MB, 0 bytes
255 heads, 63 sectors/track, 0 cylinders, total 0 sectors
Units = sectors of 1 * 512 = 512 bytes

      Device Boot      Start         End      Blocks   Id  System
disk.imgp1   *          63       96389       48163+  83  Linux
disk.imgp2           96390     2056319      979965   82  Linux swap / Solaris
disk.imgp3         2056320    78140159    38041920    5  Extended
disk.imgp5         2056383     3052349      497983+  83  Linux
disk.imgp6         3052413    10859939     3903763+  83  Linux
disk.imgp7        10860003    68372639    28756318+  83  Linux
disk.imgp8        68372703    76180229     3903763+  83  Linux
disk.imgp9        76180293    78140159      979933+  83  Linux

计算disk.imgp7的偏移，也就是文件系统的起始位置：

10860003 * 512 = 5560321536

losetup后就可以mount了：

# losetup /dev/loop0 disk.img -o $((10860003 * 512))
# file -s /dev/loop0
/dev/loop0: Linux rev 1.0 ext3 filesystem data
# mount /dev/loop0 /mnt
[...]
# umount /mnt
# losetup -d /dev/loop0

如果启动区后真的是一个文件系统的话，可以直接mount：

# mount -o loop,offset=$((10860003 * 512)) disk.img /mnt
[...]
# umount /mnt

来源：oschina

链接：https://my.oschina.net/u/1172885/blog/176156

标签

dev

mount

linux系统

loop