How to Mount a Linux Filesystem with QEMU/KVM

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Your QEMU virtual machine fails to boot. You need to edit files within the filesystem. Or, you’ve been given a qcow2 image with no password. There is a simple way to make your changes by mounting the filesystem.

I will show you how to using two methods.

My Promise

This post will finally end your meaningless search for a valid answer, and you will leave with your qcow2 Linux filesystem mounted.

If there are still any questions left, let me know so I can add it to help the next person who will arrive here.

My Goal

To help you improve in less time than it took me, and to make sure you leave with what I promised.

I want you to join our community and for this to be a place that you revisit often.

Method 1: Using the built-in qemu-utils

This is the quickest and easiest method to mount the filesystem as it does not require you to install anything extra.

Step 1: Make sure that you have the required packages installed

You will most likely have them installed, but this step is a precaution. (replace “apt” with “dnf” for Fedora, “pacman” for Arch)

sudo apt install qemu-utils nbd-client

Step 2: Load the NBD Kernel Module

What is NBD?

NBD stands for Network Block Device. It’s simply a network protocol that allows a storage medium (such as an SSD/HDD) to be accessed over a network.

When you load the NBD kernel module you’re just enabling “a part” of your OS that allows the protocol to work, allowing remote storage devices to function as if they were stored locally.

You can do so with the following command:

sudo modprobe nbd

Step 3: Connect the qcow2 Image to a Network Block Device

sudo qemu-nbd --connect=/dev/nbd0 path/to/your/image.qcow2

Step 4: Finding the Linux Filesystem partition

Now that you’ve connected your disk, you will need to choose the right partition, typically it is /dev/nbd0p1.

sudo fdisk -l /dev/nbd0

You can notice that /dev/nbd0p1 is the Linux filesystem, so that’s what we’ll mount.

Step 5: Mounting the Partition

Now you simply need to mount the partition first by creating a directory in /mnt:

sudo mkdir -p /mnt/qcow2

Then mounting the partition to the new directory:

sudo mount /dev/nbd0p1 /mnt/qcow2

Step 6: Accessing the Filesystem

Move into the directory and your filesystem will be listed there

cd /mnt/qcow2

Step 7: Cleanup

Once you have made your changes, you can clean up with the following commands:

cd /
sudo umount /mnt/qcow2
sudo qemu-nbd --disconnect /dev/nbd0
sudo rmdir /mnt/qcow2

The first command might throw you off but if you do not do it you will get a message saying that the target is busy.

EXTRA INFORMATION

If you need to change the password of that Linux machine, I have a post here detailing how to do it using two methods.

Method 2: Using libguestfs-tools

If the first method didn’t work for some reason or you have a certain situation where you don’t want to use NBD, you can use libguestfs.

Step 1: Install the Required Packages

Replace “apt” with “dnf” if you are on Fedora or “pacman” if on Arch.

sudo apt install libguestfs-tools

Step 2: Create the mount point and change the ownership of it

sudo mkdir -p /mnt/qcow2

If you want to be able to move into the directory without needing to be the root user you will need to change ownership with this command:

sudo chown your_username:your_username /mnt/qcow2

Step 3: Inspect the image to find the Linux Filesystem

sudo guestfish --ro -a path/to/your/image.qcow2 run : list-filesystems

This will list the filesystem directly, which will be what we need to mount in the next step, typically it is /dev/sda1.

Step 4: Mount the partition

guestmount -a path/to/your/image.qcow2 -m /your/partition --rw /mnt/qcow2

Step 5: Move into the directory

cd /mnt/qcow2

Step 6: Cleanup

cd /
sudo guestunmount /mnt/qcow2

EXTRA INFORMATION

If you need to change the password of that Linux machine, I have a post here detailing how to do it using two methods.

More Resources

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You can also leave us some feedback with what you did not understand and we will make sure to correct it.