Tried to open external harddrive img file

Question

I have an img file, which is packaged in a centos virtual machine. I don't know how to open it. Now I have "parted" it on another machine and found that it is an lvm structure. The question now is how do I mount the lvm part inside the .img file inside my external USB drive

Answer 1

Use losetup to associate the image file with a free /dev/loopN device:

losetup -P -f /mnt/usb/vdisk1.img

This will report the name of the actual loop device used: if there are no other loop devices in use, it will report /dev/loop0 and so you will be able to access the partitions within the image as /dev/loop0p1, /dev/loop0p2 and /dev/loop0p3. If the reported loop device name is different, the names of the partition devices will also vary accordingly.

(With the following examples, I assume that the loop device was /dev/loop0.)

Since the first partition is flagged bios_grub, it probably contains just raw embedded BIOS GRUB code, not a filesystem. Therefore there will be no need to inspect it.

If you need to access the second partition in the image, you will be able to do it now:

mkdir /mnt/image/partition2
mount /dev/loop0p2 /mnt/image/partition2

For the LVM in the third partition, first run vgscan to ensure the LVM PV is detected, then vgchange -ay to activate it:

vgscan
vgchange -ay

If these commands report a duplicate volume group error, then the VG on the image has the same name as an already-activated VG in the local system, and the VG on the image will not activate unless the name conflict is removed first. To rename a VG when you have two VGs with the same name, you'll need the VG UUID: use vgs -o +VG_UUID to view the VG UUIDs, then use vgrename to rename the duplicate, using the UUID to identify the VG to rename. Then run vgchange -ay to try and activate it again.

When vgchange -ay runs without errors, use lvs to view the names of the logical volumes on the image. Now you will be able to mount them using mount /dev/<VG>/<LV> <mountpoint> as usual.

---

To disconnect the image after you're done with it:

• first unmount all filesystems you've mounted from the image
• then deactivate the volume group with vgchange -an <VG>
• finally detach the loop device: losetup --detach /dev/loop0

Now you will be able to unmount the USB drive without device is busy errors.

Answer 2

Use losetup to create a loop device from the image

losetup -P -f /mnt/usb/vdisk1.img

the content of the image will be available as /dev/loopX, if the LVM structure on it isn't auto activated use vgs and/or vgscan to get name of the volume group, activate it using vgchange -ay <name> and then mount the logical volumes (you can get list of them using lvs and mount them using mount /dev/<vgname>/<lvname> <mountpoint>).