In this article, we will discuss a common warning encountered when using QEMU (Quick Emulator) to emulate ARM architecture. The warning message is as follows: “Image format was not specified for ‘flash0.img’ and probing guessed raw”. This warning occurs when QEMU is unable to determine the disk format for raw devices created using the
dd command. We’ll walk you through the process of resolving this warning by explicitly specifying the disk format as
To fix the QEMU warning "Image format was not specified for ‘flash0.img’ and probing guessed raw," you can explicitly specify the disk format as
raw in your QEMU command. This can be done by adding
format=raw to the
-drive options for the relevant disk images.
Understanding the Warning
Before we delve into the solution, it’s important to understand what the warning message means. When you use QEMU to emulate an ARM system, it needs to know the format of the disk images it’s working with. In this case, it’s unable to determine the format for
flash1.img, so it makes an educated guess that the format is raw.
This warning doesn’t necessarily mean something is wrong, but it does indicate that QEMU is making assumptions about your system that may not be accurate. This could potentially lead to problems down the line, so it’s best to address it.
To resolve this warning, you can modify your QEMU command to explicitly specify the disk format as
raw. Here’s an example of how to do this:
sudo qemu-system-arm -m 1024 -cpu cortex-a57 -M virt -nographic -drive file=flash0.img,format=raw,if=pflash -drive file=flash1.img,format=raw,if=pflash -drive if=none,file=xenial-server-cloudimg-arm64-uefi1.img,id=hd0 -device virtio-blk-device,drive=hd0 -device virtio-net-device,netdev=net0,mac=$randmac -netdev type=tap,id=net0
In the command above, we’ve added
format=raw to the
-drive options for
flash1.img. This explicitly tells QEMU that the disk format is raw, eliminating the need for it to guess.
Understanding the Command Parameters
Let’s break down the command parameters to better understand what they do:
-m 1024: This specifies the amount of memory for the guest system. In this case, it’s set to 1024 MB.
-cpu cortex-a57: This sets the CPU model.
-M virt: This tells QEMU to use the
virtmachine type, which is a versatile platform designed for emulating ARM systems.
-nographic: This disables graphical output so that the system is purely command-line based.
-drive file=flash0.img,format=raw,if=pflash: This tells QEMU to use
flash0.imgas a drive with a raw format. The
if=pflashpart specifies that this is a parallel flash device.
-drive file=flash1.img,format=raw,if=pflash: This does the same as the previous parameter, but for
-drive if=none,file=xenial-server-cloudimg-arm64-uefi1.img,id=hd0: This sets up a hard drive with the specified image file.
-device virtio-blk-device,drive=hd0: This connects the previously defined hard drive to the system.
-device virtio-net-device,netdev=net0,mac=$randmac -netdev type=tap,id=net0: These parameters set up a network device.
By understanding these parameters, you can better troubleshoot any issues that may arise when using QEMU.
In conclusion, the QEMU warning “Image format was not specified for ‘flash0.img’ and probing guessed raw” can be easily fixed by explicitly specifying the disk format as
raw in your command. This not only resolves the warning but also ensures that QEMU correctly interprets your disk images, preventing potential issues down the line.
You can use the
file command followed by the path to the file. For example,
file flash0.img will display the format of the
Yes, you can use different disk formats such as qcow2 or vmdk. Simply replace
raw with the desired format in the
-drive options of your QEMU command.
QEMU supports various disk formats including raw, qcow2, vmdk, vdi, and more. You can check the QEMU documentation for a complete list of supported formats.
Specifying the disk format will not significantly impact the performance of QEMU. The main purpose is to ensure that QEMU correctly interprets the disk image. The performance of QEMU is more influenced by factors such as CPU model, memory allocation, and other configuration settings.
Yes, you can use the
-drive option multiple times to specify multiple disk images or devices in your QEMU command. Just make sure to provide the appropriate file path, format, and interface (
if) for each drive.
-nographic option disables graphical output and redirects the console output to the terminal. This is useful when you want to run QEMU in a purely command-line environment without any graphical interface.
If you encounter other issues with QEMU, it’s recommended to refer to the QEMU documentation, search online forums and communities, or ask specific questions on platforms like Stack Overflow. Additionally, checking the QEMU command parameters and ensuring correct file paths and formats can help in troubleshooting.