Does QEMU have internal documentation?

Not really. The best source of internal documentation are the various KVM Forum talks and potentially talks at other conferences. These can be a bit out dated but often are good overviews of various subsystems.

I sent a patch but nobody answered. What should I do?

First of all, make sure that you followed the procedure for sending patches, and especially that you sent a copy to the corresponding support person. Qemu-devel has a very big traffic volume, so patches are easy to be lost if the right people don’t get their copies.

What versions of Linux, macOS, FreeBSD, NetBSD, OpenBSD support QEMU?

For the purposes of determining supported versions of software available in Linux, the project will consider CentOS, Debian, Fedora, openSUSE, RHEL, SLES and Ubuntu LTS. It is assumed that other distributions will provide similar versions of the software. For FreeBSD and OpenBSD, decisions will be made considering the contents of corresponding port repository, while NetBSD will use the pkgsrc repository. For macOS, Homebrew will be used.

What is QEMU disk image utility?

qemu-storage-daemon provides disk image functionality from QEMU, qemu-img and qemu-nbd in a long-running process controlled via QMP commands without running a virtual machine. It can export disk images, run block job operations, and perform other disk-related operations. The daemon is controlled via a QMP monitor and initial configuration from the command-line. Commands can be sent over a QEMU Monitor Protocol (QMP) connection. See the qemu-storage-daemon-qmp-ref manual page for a description of the commands. The daemon runs until it is stopped using the quit QMP command or SIGINT/SIGHUP/SIGTERM.

How to Recover Data from a QEMU Virtual Machine?

In today’s article, read about how to create a QEMU hypervisor in a Windows operating system, create a virtual machine with Linux, and how to recover its data.

Contents

Virtualization is the easiest way to run one more operating system on your PC without having to install it directly to its hard disk. Instead, the additional operating system is installed to a virtual disk which is represented by a special container file. The most popular hypervisors are VirtualBox and VMware, and they both have a wide range of functions and an easy-to-understand graphical interface.

QEMU is a free open-source program designed to emulate various software products and operating systems. This tool uses hardware virtualization and supports a long list of architectures to be emulated (x86, ARM, MIPS, PowerPC, m68k, Alpha, SPARC, SH-4, CRISv2, MicroBlaze).

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🦅 How to Recover Data from a QEMU Virtual Machine. Installing a QEMU Hypervisor in Windows 🦅

How to install QEMU in Windows

The first thing you need for installation is to download a QEMU distribution for Windows. You can get it from the official website – www.qemu.org/download/#windows.

You can choose between 32-bit and 64-bit versions. Choose the latter one and download the corresponding file. Install the program and leave all options at their default values – just don’t change anything.

How to use QEMU in Windows

Unlike VirtualBox and similar hypervisors, QEMU doesn’t have a graphical interface: it can be operated with the command prompt only. Let’s download an ISO image of the operating system which we will install onto the virtual machine. After that, we need to add the QEMU path to the environment variables.

To do that, open the File Explorer and copy the path to the folder containing the program.

С:\Program files\qemu

Then right-click on “This PC” and open “Properties”.

“Advanced system settings”. In the Advanced tab, open “Environment Variables”.

In the field “User variables”, double-click on “Path”.

Then click “New” and paste the path to the QEMU folder that you have copied before. Click OK to save the changes and then click OK again to leave the settings.

Before installation, you need to enable a specific Windows component - Windows Hypervisor Platform - or the virtual machine may not start properly. Also, it is recommended to enable Hyper-V or HAXM accelerator to make the virtual machine work faster.

To do it, use the setting “Turn Windows features on or off”. Enable the platform.

The list of commands and settings used to create and manage virtual machines is quite long, but you only need a few to start working.

Launch the Command Prompt as Administrator and begin the installation. For starters, let’s create a folder for virtual machines – C:\qemu. Then go to that folder with the command prompt. Now you need to create a virtual hard disk of 15 to 20 GB. Use the following command:

qemu-img create -f qcow2 ubuntu.qcow2 20G

Where the setting -f indicates the file format, followed by the file name and the file size is given at the end of the command.

Then enter another command to create a virtual machine: it includes certain settings.

The architecture - qemu-system-x86_64.exe

The boot drive - -boot c

Virtual machine RAM size - -m 2048

The number of processors allocated for this machine - -smp 2

The path to the folder containing the program - -L "C:\Program Files\qemu"

Graphics - -vga std

Sound - -soundhw es1370

Virtual disk - -boot menu=on -hda ubuntu.qcow2

Path to ISO image - -cdrom "C:\ubuntu.iso"

The time and network settings - -rtc base=localtime,clock=host -net nic,model=ne2k_pci -net user

qemu-system-x86_64.exe -boot c -m 2048 -smp 2 -L "C:\Program Files\qemu" -vga std -soundhw es1370 -boot menu=on -hda ubuntu.qcow2 -cdrom "D:\ubuntu.iso" -rtc base=localtime,clock=host -net nic,model=ne2k_pci -net user

The command to create a QEMU virtual machine

When you enter the command, the QEMU window appears, the virtual machine boots and the installation of the operating system begins.

In my case, this is Ubuntu. After the installation is complete and the virtual machine restarts, it boots with the operating system you have installed, and it is now ready for work.

How to create a virtual machine with QtEmu

Also, there is another way to create a virtual machine with the help of the QtEmu graphical interface. This open-source utility for QEMU is designed to simplify the process of creating and managing a virtual machine.

Let’s visit the program’s official website, follow the link to gitlab and download the installation file.

https://qtemu.org

https://gitlab.com/qtemu/gui

Remember to enable such Windows feature as Windows Hypervisor Platform if you forgot to turn it on before: this feature should be running, otherwise the virtual machine may not start.

To do it, open “Programs and Features” - “Turn Windows features on or off”. Enable the platform.

Start the installer and choose where to install the program. After the installation is over, put the program’s shortcut on the desktop for your convenience, and create a folder to store virtual machine files.

When you start the program for the first time, specify the following settings. In the first field - the path to the folder where QEMU is installed. In the second field - the path to the QEMU-img file. And in this field - the path to the folder where virtual machine files are stored, and then click “Finish”.

To create a new virtual machine, click “Machine” – “New Machine”, give a name, operating system type, select its version, and then click “Next”. In this Machine page, click “Next” unless you need to choose a specific motherboard setup.

After that, you should choose a proper CPU type, and configure the graphics, sound and network settings. If you get the wrong CPU, the virtual machine may not boot properly.

Select a virtual machine hardware configuration

Now you need to choose the accelerator - the default choice is HAXM. Some computers may not support this technology so I recommend to uncheck this box for HAXM and choose TCG instead, then click “Next”.

Sometimes users complain that nothing happens when they start a virtual machine. This problem can be caused by HAXM, so it’s always better to go for TCG to make sure the virtual machine will work on most computers.

After that, set the RAM size for the virtual machine, and create a virtual hard disk. Specify the disk size and type. Then click “Finish” to complete setup.

After that, right-click on the machine and choose “Machine Settings”.

Access “Boot options” and check the box for CDROM, then bring it to the top and enable boot menu.

Then jump to the Media tab, click on the disk icon and give the path to an ISO image file of the operating system, and then click “Save”.

Select the virtual machine and click here to start it. The QEMU window opens, the installer boots, and then the installation of the operating system begins.

When the installation process is over, the virtual machine will be ready to use.

How to recover QEMU data

All right, we have just explored the process of installing QEMU and creating a virtual machine. But what should you do if - for any reason - you lost access to your virtual machine, deleted the machine files by accident, or lost some mission-critical data stored on the virtual hard disk?

If that’s your case, use a specialized data recovery tool - Hetman Partition Recovery - which can work successfully with most file formats used in popular hypervisors.

Partition Recovery™ 4.9

The tool recovers data from any devices, regardless of the cause of data loss.

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It supports all popular file system formats and it can help you restore data after deleting, formatting, and hardware or software errors.

In a Windows operating system, all you have to do is to download and install the program. If you’re using a different operating system, take the hard disk out of your computer and connect it to a Windows PC.

If you want to recover virtual machine files, connect the disk where virtual disk files were stored, and scan it with Hetman Partition Recovery.

Right-click on the disk and choose “Open”. Select the scan type - “Fast scan” or “Full analysis” if the first option is not available. Before starting “Full analysis”, choose the file system and click “Next”.

In my case, “Fast scan” is available. Find the folder where the virtual machine files were stored, select the files you want to restore, click “Recovery”, specify the path where you’d like to save the files, and click “Recovery” again.

You will find the recovered files in the directory you have chosen. Here some typical extensions of virtual machine files: qcow, qcow2, .img, .cow, .qed, .vmdk, .vdi, .vhd, .vhdx, .hdd, .hds.

If you failed to boot a virtual machine after system repair operations, or if there is an error when you try to start it, don’t give up: use our program to open that file and recover all of its data.

To do it, open “Tools” - “Mount Disk” - and you’ll find two ways to mount it: choose a RAW disk image if you’re dealing with conventional disks, or choose Virtual Machines. You can see the list of files and tools that our program supports.

Check the required image type, give the path to the folder containing virtual hard disk files, and click “Select Folder”. The program will display all virtual machine files which exist in such folder, and you can uncheck the boxes for the ones you don’t need now.

To begin searching for data, right-click on the disk and choose “Open”. Then choose analysis type. We recommend starting with “Fast scan”. If the program can’t find the missing files, then go for “Full analysis”.

The program can find all files remaining on the disk without difficulty. The red cross indicates the ones which have been deleted. Click on a file to see its contents in the preview window. With this quick search option you can find a specific file by its name.

Recover files from a virtual machine disk

Select the files you need to restore and click “Recovery”, specify the disk where to save the files and click “Recovery” again.

Conclusion

Summing up, what can we say about the QEMU hypervisor? It’s difficult to say if it’s better or worse than VirtualBox or VMware. More likely, it’s an alternative method of virtualization, and it has its own pros and cons. QEMU is less convenient, it requires you to know the manuals, and its performance is very moderate. To accelerate its work in Windows, you need to install and configure HAXM, the Hardware Accelerated Execution Manager. On the other hand, this tool lets you emulate work on various architectures which are not supported by popular hypervisors. And if you ever lose any data - now you know which recovery tool can bring it back in a most efficient way.