Focusing on the VM Context: How the Kernel and Initramfs Are Loaded

Given the observations, we can now focus on the VM context and explore how the kernel and initramfs might be loaded in a paravirtualized KVM environment. Since GRUB is confirmed to be the bootloader (via the MBR), but the grub.cfg file does not contain the expected linux and initrd parameters, it’s likely that the boot process is being handled in a non-standard way.

Key Observations

GRUB is the Bootloader:
- The MBR contains GRUB, so GRUB is responsible for loading the kernel and initramfs.
grub.cfg Does Not Contain linux or initrd: - This suggests that GRUB is not using a standard configuration file to load the kernel and initramfs.
Kernel and Initramfs Exist in /boot/:
- The kernel (vmlinuz-<version>) and initramfs (initrd.img-<version>) files exist in /boot/ and match the running kernel version (uname -r).
VM is Paravirtualized:
- The VM is running under KVM with paravirtualized drivers, which can influence how the boot process works.

Possible Mechanisms for Loading the Kernel and Initramfs

Given the above observations, here are the most likely mechanisms for how the kernel and initramfs are being loaded:

Embedded Configuration in GRUB:

GRUB might be using an embedded configuration to load the kernel and initramfs. This means the boot parameters are hardcoded into GRUB’s core image (core.img) rather than being read from grub.cfg.

How to Check:
- Inspect the GRUB environment variables: .. code-block:: bash
  
  sudo grub2-editenv list
- Check if GRUB’s core.img contains embedded configuration: .. code-block:: bash
  
  strings /boot/grub2/i386-pc/core.img | grep -iE ‘linux|initrd’
Direct Kernel Boot (via Hypervisor):

In some paravirtualized environments, the hypervisor (KVM) can directly load the kernel and initramfs into memory, bypassing the bootloader. This is often done using the -kernel and -initrd options when starting the VM.

How to Check:
- Review the VM’s configuration file (e.g., XML file for libvirt or command-line options for qemu-kvm).
- Check the hypervisor logs for evidence of direct kernel boot:
```
sudo journalctl -u libvirtd
```
Chainloading from Another Bootloader:

GRUB might be chainloading another bootloader or boot mechanism that handles the loading of the kernel and initramfs.

How to Check:
- Inspect the grub.cfg file for chainloader entries: .. code-block:: bash
  
  cat /boot/grub2/grub.cfg | grep chainloader
Custom GRUB Module or Script:

GRUB might be using a custom module or script to load the kernel and initramfs. This could be part of a specialized VM setup.

How to Check:
- Look for custom GRUB modules in /boot/grub2/i386-pc/: .. code-block:: bash
  
  ls /boot/grub2/i386-pc/
- Check for custom scripts in /etc/grub.d/:
```
ls /etc/grub.d/
```

Next Steps

Check GRUB Environment Variables:
```
sudo grub2-editenv list
```

Inspect GRUB’s core.img:

strings /boot/grub2/i386-pc/core.img | grep -iE 'linux|initrd'

Review VM Configuration:

Check the VM’s configuration file (e.g., libvirt XML or qemu-kvm command line) for direct kernel boot options.
Check Hypervisor Logs:
```
sudo journalctl -u libvirtd
```
Verify Chainloading:

Check for chainloader entries in grub.cfg or other bootloaders in /boot/.

Summary of Likely Mechanisms

Embedded Configuration in GRUB:
- GRUB’s core.img might contain hardcoded paths to the kernel and initramfs.
Direct Kernel Boot via Hypervisor:
- The hypervisor (KVM) might be directly loading the kernel and initramfs.
Chainloading from Another Bootloader:
- GRUB might be chainloading another bootloader or mechanism.
Custom GRUB Module or Script:
- A custom GRUB module or script might be handling the boot process.