Preparation of QEMU Disk Image

A disk image is a computer file that encapsulates the full contents and organizational structure of a storage device. The concept has been extended to include any such file, regardless of whether it originates from an actual physical medium or is created virtually (Disk image - Wikipedia, 2026).

QEMU supports a wide range of disk image formats, including growable images (which expand as non‑empty sectors are written), as well as compressed and encrypted images (Disk Images — QEMU documentation, 2026).

In laboratory exercises, the qcow2 format will be used as QEMU’s second‑generation Copy On Write disk image type. A qcow2 image encapsulates the complete contents and structure of a virtual disk while supporting snapshots, compression, encryption, and growable size. Compared to the raw format, qcow2 offers greater flexibility and storage efficiency, whereas raw provides only maximum performance (2.4. Storage Formats for Virtual Disks | Technical Reference | Red Hat Virtualization | 4.3 | Red Hat Documentation, 2026). Two approaches exist for preparing an operating system on a qcow2 image: (a) manual installation on the newly created image, or (b) deployment of a pre‑built cloud image.

As the operating system, it is suggested to use Debian Linux, recommended for its stability, security and freedom, although another Linux distribution may also be chosen depending on preference.

(a) Manual Installation of Operating System:

On Windows

1. Open Administrator: Command Prompt by typing cmd in the Start menu, right‑clicking to select Run as administrator, or alternatively navigating through Windows System → Command Prompt.
2. Create working folder — for example, create a directory C:\VMs with mkdir C:\VMs, then switch into it using cd C:\VMs. You may choose any convenient location instead of C:\VMs. To move between drives, use the drive letter followed by a colon (e.g. D: to switch to drive D).
3. Create qcow2 image by running qemu-img create -f qcow2 debian.qcow2 20G, where debian.qcow2 is the image file name and 20G sets the virtual disk size (Disk Images — QEMU documentation, 2026).
4. Download Debian ISO by clicking Download on the site and saving the file (e.g. debian-12.6.0-amd64-netinst.iso) into working folder such as C:\VMs.
5. Start QEMU by mounting the qcow2 hard disk image and the Debian installer ISO image:
   

   qemu-system-x86_64.exe -m 2G -smp 2 -boot order=dc -hda debian.qcow2 -cdrom debian-12.6.0-amd64-netinst.iso

   Where:

   • -m 2G specifies 2GB of memory
   • -smp 2 sets two CPU cores
   • -boot order=dc means boot first from CD-ROM (d), then from hard disk (c)
   • -hda debian.qcow2 defines the virtual hard disk in qcow2 format
   • -cdrom debian-12.6.0-amd64-netinst.iso attaches the Debian installer ISO as a virtual CD-ROM

   More details about these parameters can be found on the page Invocation — QEMU documentation.

   Internet will be available in the guest system right away and no additional configuration is required (Network emulation — QEMU documentation, 2026).

6. Install Debian Linux according to the guide 4.2. Installing, Step by Step available at the Debian Handbook.

   Pressing Ctrl + Alt + G releases the grab.

7. After installation, Debian should be started with the following command: qemu-system-x86_64.exe -m 2G -smp 2 -hda debian.qcow2

   In case of problems with QEMU, use the help command: qemu-system-x86_64.exe --help

On Android

1. On internal storage or on the SD card, create a directory such as /storage/emulated/0/VMs (internal phone storage) or /storage/XXXX-XXXX/VMs (where XXXX-XXXX is the SD card identifier, e.g. /storage/1234-5678/) to store disk images and ISO files.
2. As in Step 4 of the On Windows section, download the Debian installer ISO (e.g. debian-12.6.0-amd64-netinst.iso) and place it into working folder.
3. Open Limbo x86 in the app drawer, then in the menu (three vertical dots) select Create Machine, enter a name for the Virtual Machine, and press Create.
4. Configure Virtual Machine settings by set the following parameters:
   • User Interface (Display : SDL (Simple DirectMedia Layer, provides direct graphics and audio output), Keyboard : en-us, Mouse : ps2)
   • Board (Machine Type : pc, CPU Model: qemu64, CPU Cores: 2, RAM Memory (MB): 2000
   • Board → Advanced options (toggles): Enable MTTCG (multi‑threaded emulation): Disable, Disable HPET (high‑precision timer): Enable, Enable KVM (Kernel-based Virtual Machine acceleration): Disable, Disable TSC (disables time‑stamp counter): Enable; Disable ACPI (Advanced Configuration and Power Interface): Disable)
   • Disks (In the field right Hard Disk A where it shows None, select New, enter a name for image (e.g. debian.qcow2), choose 20 GB (Growable) as size and press Change Directory, select your working folder, then press Create. The disk image file will be stored in working directory.
   • Removable (CDROM (toggle): Enabled ). In the field where it shows None, select Open and choose the Debian installer ISO image in working directory.
   • Boot (Boot from Device: CDROM)
   • Graphics (Video Display: std)
   • Audio (Sound Card: None)
   • Network (Network: User, Network Card: Default, DNS Server: 8.8.8.8)
5. Press Play button and install Debian according to Step 6 of the On Windows. Control of the virtual machine can be carried out through the menu (vertical three dots).
6. After installation, in the virtual machine settings change parameter Boot (Boot from Device: Hard Disk). The system will then boot from the first disk (Hard Disk A).

(b) Deployment of Pre‑built Cloud Image

On Windows

1. Complete Step 1 and Step 2 of subsection On Windows in section (a) Manual Installation of Operating System.
2. Go to the webpage Debian Official Cloud Images, scroll down, select the latest Debian build (Trixie), open the latest directory, download the file debian‑13‑nocloud‑amd64.qcow2, and place it directly into the working directory (e.g. C:\VMs).

   Verification can be performed by downloading the SHA512SUMS file in the same directory, running Get-FileHash debian-13-nocloud-amd64.qcow2 -Algorithm SHA512 in PowerShell on Windows, and comparing the output with the published checksum to confirm authenticity.

   The nocloud image is chosen because it is self‑contained, does not rely on external cloud‑init metadata, and is therefore ideal for straightforward local QEMU deployment under Windows.

3. For increasing space on the virtual disk, execute the command from Command Prompt in the working directory
   qemu-img resize debian-13-nocloud-amd64.qcow2 +20G, where +20G means adding 20 gigabyte to the current disk size (QEMU disk image utility — QEMU documentation, 2026).

   After resizing the qcow2 image with qemu-img, extra steps are needed inside the VM. qemu-img only enlarges the virtual disk container. The partition table and filesystem inside the OS remain at their old size. Until the partition is expanded and the filesystem grown, the new space is invisible and cannot be used.

4. Run the virtual machine by analogy with Step 7 of subsection On Windows in section (a) Manual Installation of Operating System.
5. Enlarge partition boundaries and filesystem within the virtual machine.
   • Log in as the superuser (root) by typing root at the login: prompt and pressing Enter, since no password is set. If a password is required, the characters entered will not be displayed. After a successful login, the system displays the root shell prompt root@localhost:~# █, indicating that you are now operating as the superuser. In the shell prompt, ~ marks the home directory, while # means root and $ means a regular user.
   • Enter lsblk to list all block devices and partitions, then compare the total disk size with the size of the root partition / to see how much space can potentially be added (lsblk(8) - Linux manual page, 2026).

     root@localhost:~# lsblk
     NAME    MAJ:MIN RM  SIZE RO TYPE MOUNTPOINTS
     fd0       2:0    1    4K  0 disk
     sda       8:0    0   23G  0 disk
     ├─sda1    8:1    0  2.9G  0 part /
     ├─sda14   8:14   0    3M  0 part
     └─sda15   8:15   0  124M  0 part /boot/efi
     sr0      11:0    1 1024M  1 rom
     

     On lsblk:
     SIZE for disk sda shows the total capacity (23G).
     SIZE for partition sda1 shows the current root / size (2.9G).
     The difference indicates how much the root partition could be expanded, provided adjacent free or unused space exists.
     This is a breakdown of the lsblk table column, all other available fields can be listed with lsblk --list-columns or lsblk -H:

     Column	Meaning
     NAME	Device or partition name (e.g., sda, sda1).
     MAJ:MIN	Major and minor device numbers used by the kernel to identify the driver and specific device. Major device numbers map to drivers such as 1 for RAM disks (/dev/ram0), 3 for IDE (/dev/hda), 7 for loop devices (/dev/loop0), 8 for SCSI/SATA (/dev/sda), 9 for MD RAID (/dev/md0), 11 for CD‑ROM (/dev/sr0), 65–71 for additional SCSI disks (/dev/sdb, /dev/sdc), 128 for USB storage, and 179 for MMC/SD cards (/dev/mmcblk0). Minor numbers identify the specific device or partition handled by a driver, for example 8:0 is the whole disk /dev/sda, 8:1 is its first partition /dev/sda1, and 8:2 is the second partition /dev/sda2.
     RM	Removable flag: 1 means removable (USB, SD card), 0 means fixed disk.
     SIZE	Total size of the device or partition.
     RO	Read‑only flag: 1 means the device is read‑only, 0 means writable.
     TYPE	Type of entry: disk (whole device), part (partition), rom (optical media).
     MOUNTPOINT	Directory where the partition is mounted (e.g., /, /home, /media/usb).

   • Execute apt update -y && apt upgrade -y to refresh the package lists and automatically upgrade all installed packages to their latest versions. The -y flag ensures the process runs non‑interactively, accepting all prompts (APT User's Guide, 2026).
   • Install parted with apt install parted -y to manage disk partitions — it can display partition tables, create, resize, and delete partitions, and show filesystem information (parted(8) — Linux manual page, 2026).
     
     • Open parted:

       root@localhost:~# parted /dev/sda
       GNU Parted 3.6
       Using /dev/sda
       Welcome to GNU Parted! Type 'help' to view a list of commands.
       (parted) █
       

       Launches interactive mode for disk sda.
     • Inspect partitions by typing print at the parted prompt and pressing Enter to display the current partition table with sizes, types, and filesystem information.

       (parted) print
       Warning: Not all of the space available to /dev/sda appears to be used, you can
       fix the GPT to use all of the space (an extra 41943040 blocks) or continue with
       the current setting?
       (Fix/Ignore?) █

       This warning indicates that the GPT partition table on /dev/sda does not cover the full disk capacity — about 41,943,040 blocks remain unused — so type Fix and press Enter to update the GPT and make the entire space available for partitioning.

       Fix/Ignore? Fix
       Model: ATA QEMU HARDDISK (scsi)
       Disk /dev/sda: 24.7GB
       Sector size (logical/physical): 512B/512B
       Partition Table: gpt
       Disk Flags:
       
       Number  Start   End     Size    File system  Name  Flags
       14      1049kB  4194kB  3146kB                     bios_grub
       15      4194kB  134MB   130MB   fat16              boot, esp
        1      134MB   3220MB  3086MB  ext4
       
       (parted) █

     • Resizes partition 1 by typing resizepart 1 100% to extend it until the end of the disk (here 100% means all available space) and confirm the warning when prompted.

       (parted) resizepart 1 100%
       Warning: Partition /dev/sda1 is being used. Are you sure you want to continue?
       Yes/No? Yes
       (parted) █

     • Check the state of the disk by typing print at the parted prompt and pressing Enter

       (parted) print
       Model: ATA QEMU HARDDISK (scsi)
       Disk /dev/sda: 24.7GB
       Sector size (logical/physical): 512B/512B
       Partition Table: gpt
       Disk Flags:
       
       Number  Start   End     Size    File system  Name  Flags
       14      1049kB  4194kB  3146kB                     bios_grub
       15      4194kB  134MB   130MB   fat16              boot, esp
        1      134MB   24.7GB  24.6GB  ext4
       
       (parted) █

       The partition size has been increased.
     • Type quit and press Enter at the parted prompt to exit — no need to adjust fstab, since partition resizing does not change mount points.
   • After resizing the partition, expand the filesystem (for ext4) by running: resize2fs /dev/sda1

     root@localhost:~# resize2fs /dev/sda1
     resize2fs 1.47.2 (1-Jan-2025)
     Filesystem at /dev/sda1 is mounted on /; on-line resizing required
     old_desc_blocks = 1, new_desc_blocks = 3
     The filesystem on /dev/sda1 is now 5996539 (4k) blocks long.
     
     root@localhost:~# █

   • Verify the result with lsblk to confirm the new capacity is recognized.

     root@localhost:~# lsblk
     NAME    MAJ:MIN RM  SIZE RO TYPE MOUNTPOINTS
     fd0       2:0    1    4K  0 disk
     sda       8:0    0   23G  0 disk
     ├─sda1    8:1    0 22.9G  0 part /
     ├─sda14   8:14   0    3M  0 part
     └─sda15   8:15   0  124M  0 part /boot/efi
     sr0      11:0    1 1024M  1 rom
     root@localhost:~# █

6. Shut down the machine from the command line, use: shutdown -h now