# Create an Azure Linux image for Arm

## In this learning path

- [Introduction](https://learn.arm.com/learning-paths/servers-and-cloud-computing/azure-vm/)
- [Build and run Azure Linux 3.0 on an Arm-based Azure virtual machine](https://learn.arm.com/learning-paths/servers-and-cloud-computing/azure-vm/background/)
- [Create an Azure Linux image for Arm](https://learn.arm.com/learning-paths/servers-and-cloud-computing/azure-vm/azure-vm/)
- [Transfer the image to Azure](https://learn.arm.com/learning-paths/servers-and-cloud-computing/azure-vm/save-image/)
- [Start an Azure virtual machine with the new image](https://learn.arm.com/learning-paths/servers-and-cloud-computing/azure-vm/start-vm/)
- [Next Steps](https://learn.arm.com/learning-paths/servers-and-cloud-computing/azure-vm/_next-steps/)

## How do I create an Azure Linux image for Arm?
You can view the Azure Linux 3.0 project on [GitHub](https://github.com/microsoft/azurelinux). The project README includes links to ISO downloads.

Using [QEMU](https://www.qemu.org/), you can create a raw disk image, boot a virtual machine with the ISO, and install the operating system. After installation is complete, you’ll convert the image to a fixed-size VHD, upload it to Azure Blob Storage, and use the Azure CLI to create a custom Arm image.

## How do I download the Azure Linux ISO and create a raw disk image?
Use `wget` to download the Azure Linux ISO image file:

```bash
wget https://aka.ms/azurelinux-3.0-aarch64.iso
```

Create a 32 GB empty raw disk image to install the OS:

```bash
qemu-img create -f raw azurelinux-arm64.raw 34359738368
```

> **Note**: You can change the disk size by adjusting the value passed to `qemu-img`. Ensure it meets the minimum disk size requirements for Azure (typically at least 30 GB).

## How do I install Azure Linux on a raw disk image using QEMU?
Use QEMU to boot the operating system in an emulated Arm VM.

```bash
qemu-system-aarch64 \
  -machine virt \
  -cpu cortex-a72 \
  -m 4096 \
  -nographic \
  -bios /usr/share/qemu-efi-aarch64/QEMU_EFI.fd \
  -drive if=none,file=azurelinux-arm64.raw,format=raw,id=hd0 \
  -device virtio-blk-device,drive=hd0 \
  -cdrom azurelinux-3.0-aarch64.iso \
  -netdev user,id=net0 \
  -device virtio-net-device,netdev=net0
```

Follow the installer prompts to enter the hostname, username, and password. Use `azureuser` as the username to ensure compatibility with later steps.

> **Note**: The installation process takes several minutes.

At the end of installation, confirm the reboot prompt. After rebooting into the newly-installed OS, install and enable the Azure Linux Agent:

```bash
sudo dnf install WALinuxAgent -y
sudo systemctl enable waagent
sudo systemctl start waagent
sudo poweroff
```

> **Note**: It can take a few minutes to install the agent and power off the VM.

## How do I convert a raw disk image to a fixed-size VHD for Azure?
Now that the raw disk image is ready for you to use, convert it to fixed-size VHD, which makes it compatible with Azure.

```bash
qemu-img convert -f raw -o subformat=fixed,force_size -O vpc azurelinux-arm64.raw azurelinux-arm64.vhd
```

> **Note**: VHD files include a 512-byte footer at the end. The `force_size` flag ensures the final image size matches the requested virtual size. Without this, QEMU might round the size or adjust for footer overhead (especially when converting from raw to VHD). The `force_size` flag forces the final image to match the original size. This is required for Azure compatibility, as it avoids rounding errors and ensures the VHD ends at a whole MB or GB boundary.

In the next step, you’ll upload the VHD image to Azure and register it as a custom image for use with Arm-based virtual machines.