When dealing with virtual machines in LXD or any other QEMU-based environments manually mounting a VM’s disk image can allow you to inspect its contents and retrieve data. This article walks you through the process of mounting a VM disk image for troubleshooting and data recovery.

1. Create a Mount Directory and Locate the VM Image

First, create a directory where you will mount the VM’s filesystem:

$ mkdir -p /root/Desktop/havm

Now, find to the directory where the VM disk image is stored. For those using LXD / Incus that’s typically under:

$ cd /var/lib/lxd/virtual-machines

In this directory, you’ll find a sub-directory for each VM and inside those a disk image named root.img.

2. Calculate Partition Offsets

Now you know the image is at /var/lib/lxd/virtual-machines/havm/root.img you may be tempted to mount it with mount-o loop root.img /root/Desktop/havm, but that doesn’t work.

The problem is that the .img files are not images of a partition, but of a whole disk – that means they start with the EFI partition. You have to find out the start of the OS partition and mount it with the offset option of mount. Use fdisk to list the partition details:

$ fdisk -l /var/lib/lxd/virtual-machines/havm/root.img

Disk root.img: 32 GiB, 34359738368 bytes, 67108864 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
Disklabel type: gpt
Disk identifier: 894818E3-EDC5-46A0-9E2D-1593EDC6BAD4

Device       Start      End  Sectors  Size Type
root.img1     2048    67583    65536   32M EFI System
root.img2    67584   116735    49152   24M Linux filesystem
root.img3   116736   641023   524288  256M Linux filesystem
root.img4   641024   690175    49152   24M Linux filesystem
root.img5   690176  1214463   524288  256M Linux filesystem
root.img6  1214464  1230847    16384    8M Linux filesystem
root.img7  1230848  1427455   196608   96M Linux filesystem
root.img8  1427456 67108830 65681375 31.3G Linux filesystem

The offset for mounting a partition is calculated using:

Offset = Start Sector * Sector Size

In my case the OS partition (root.img8) starts at 1427456 and I’ve a sector size of 512, so:

Offset = 1427456 * 512 = 730857472 bytes

3. Working With the Image

Now that we have the correct offset, we can mount the partition using the following:

$ mount -o loop,offset=730857472 /var/lib/lxd/virtual-machines/havm/root.img /root/Desktop/havm

After running this command, the filesystem should now be accessible at /root/Desktop/havm. Use the Terminal or the GUI file explorer to retrieve the data you need.

After you have finished working with the mounted image, unmount it properly to avoid data corruption:

$ umount /root/Desktop/havm