Determining the Bootloader and Kernel/Ramdisk Loading in a KVM VM

We are trying to determine which bootloader is in use by the VM and confirm from where the kernel (vmlinuz) and initial RAM disk (initrd) are being loaded. Since the VM is running on KVM (Kernel-based Virtual Machine), let’s explore the possible bootloaders and how they load the kernel and initramfs.

Step 1: Verify the Bootloader in Use

To determine the bootloader in use, we can check the following:

  1. Check for GRUB:

    • GRUB is the most common bootloader for Linux systems. Check if GRUB is installed and configured: - Look for the GRUB configuration file:

      • Check if GRUB is installed:

  2. Check for systemd-boot:

    • Although bootctl status confirmed the system is not booted with EFI, it’s worth checking for systemd-boot configuration files: - Look for the systemd-boot configuration directory:

  3. Check for Other Bootloaders:

    • If neither GRUB nor systemd-boot is in use, the system might be using a different bootloader (e.g., Syslinux, LILO, or a custom bootloader). - Look for configuration files in /boot/:

Step 2: Confirm Kernel and Initramfs Loading

Once the bootloader is identified, we need to confirm how the kernel and initramfs are being loaded.

  1. If GRUB is in Use:

    • The GRUB configuration file (/boot/grub2/grub.cfg) should contain entries like:

    • If these entries are missing, GRUB might be using a custom configuration or chainloading another bootloader.

  2. If systemd-boot is in Use:

    • The systemd-boot configuration files in /boot/loader/entries/ should contain entries like:

  3. If Another Bootloader is in Use:

    • Check the bootloader’s configuration files (e.g., syslinux.cfg for Syslinux or lilo.conf for LILO) for references to the kernel and initramfs.

Step 3: Analyze the Boot Process

To further understand how the kernel and initramfs are being loaded, we can analyze the boot process:

  1. Check the Kernel Command Line:

    • Run the following command to inspect the kernel command line:

    • Look for parameters like initrd= or root= that indicate how the kernel and initramfs are loaded.

  2. Inspect the dmesg Output:

    • The dmesg output provides detailed logs of the boot process. Look for messages related to the kernel and initramfs loading:

  3. Check for Paravirtualized Drivers:

    • Since the VM is running on KVM, look for messages related to paravirtualized drivers (e.g., virtio):

Step 4: Verify Hypervisor Configuration

Since the VM is running on KVM, the hypervisor configuration might influence how the kernel and initramfs are loaded:

  1. Check the VM Configuration:

    • Verify the VM’s configuration file (e.g., /etc/libvirt/qemu/<vm-name>.xml for libvirt) to ensure the correct bootloader and kernel are specified.

  2. Check for Direct Kernel Boot:

    • Some hypervisors allow direct kernel boot, bypassing the bootloader. Check if the VM is configured to boot the kernel directly:

Summary

  1. Verify the bootloader in use (GRUB, systemd-boot, or another bootloader).

  2. Confirm how the kernel and initramfs are being loaded by inspecting the bootloader configuration files.

  3. Analyze the boot process using dmesg and the kernel command line.

  4. Verify the hypervisor configuration to ensure the correct bootloader and kernel are being used.

Let me know if you need further clarification or assistance!