Virtual Machine Boot Sequence Explained

What Really Happens When You Power on a Virtual Machine?

Powering on a virtual machine (VM) looks simple—just one click and the VM starts running.
But behind that click, many things happen in a very precise order. Understanding this process helps system administrators, cloud engineers, and even beginners troubleshoot issues faster and design better infrastructure.

Below Steps inside virtual machine from the moment you press Power On to the login screen.

1. You Click “Power On”

When you click Power On in platforms like VMware, Hyper-V, KVM, or VirtualBox, you’re not starting a physical machine. Instead, you’re sending a request to the hypervisor (the software that manages virtual machines).

The hypervisor now takes responsibility for bringing your VM to life.

     2. Hypervisor Allocates Resources

Before the VM can run, the hypervisor checks and assigns resources:

• CPU cores (virtual CPUs mapped to physical CPUs)
• RAM (reserved from the host system)
• Disk access (VMDK, VHD, QCOW2, etc.)
• Network interface (virtual NICs)
• BIOS or UEFI firmware

If enough resources are available, the process continues.
If not, the VM fails to power on.

    3. Virtual Hardware Comes Alive

Now the hypervisor “builds” a virtual computer:

• Virtual motherboard
• Virtual CPU
• Virtual RAM
• Virtual disk controller
• Virtual network card

To the operating system inside the VM, this looks like real hardware.

4. BIOS or UEFI Starts (Just Like a Physical PC)

The VM firmware (BIOS or UEFI) now starts running.

It performs basic checks similar to a physical machine:

• Is memory available?
• Is a boot device present?
• Which device should boot first?

This step is very fast in VMs compared to physical servers.

 5. Bootloader Is Loaded

The firmware finds the boot disk and loads the bootloader, such as:

• GRUB (Linux)
• Windows Boot Manager

The bootloader’s job is simple:
 Load the operating system kernel into memory.

6. Operating System Kernel Starts

Now the real OS startup begins.

The kernel:

• Initializes CPU scheduling
• Detects virtual hardware
• Loads drivers for disk, network, and memory
• Mounts the root filesystem

At this stage, the VM is fully “alive,” but not ready for users yet.

7. System Services and Background Processes Start

After the kernel is ready, the OS starts system services:

• Networking services
• Logging services
• Security services
• Time synchronization
• Database, web, or application services (if configured)

On Linux, this is usually managed by systemd.
On Windows, the Service Control Manager handles this step.

8. VM Tools / Guest Agents Load

If installed, tools like:

• VMware Tools
• Hyper-V Integration Services
• QEMU Guest Agent

start running.

These improve:

• Performance
• Time sync
• Clipboard sharing
• Clean shutdown and restart support

9. Login Screen or Console Appears

Finally, the VM reaches a usable state:

• Linux shows a login prompt
• Windows shows the login screen
• Servers may start applications automatically

Your virtual machine is now fully powered on and operational.

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