Linux – Running bzImage in QEMU: Unable to mount root fs on unknown-block(0.0)

linuxlinux-kernelqemu

I compiled the kernel by doing make menuconfig and make. I was trying to run the bzImage in qemu, by doing qemu -kernel bzImage but it didn't work out with the error message:

Unable to mount root fs on unknown-block(0.0)

Linux kernel error

How can I fix it? How can I run the bzImage in qemu?

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It did work out. The kernel booted fine. The error is:

Unable to mount root fs on unknown-block(0.0)

The kernel is looking for a root filesystem. You need to provide one. You can't interact with a kernel without running processes on it, and the initial process has to be loaded from somewhere: when the kernel starts, it mounts a filesystem (the root filesystem) on the directory /, then runs the program /sbin/init. The init program is normally in charge of running boot scripts and starting services including programs that let users log in.

You must make sure that the kernel is able to mount the root filesystem. It must have drivers for the filesystem type and for all the layers involved in the block device (disk controller (SCSI/SATA/IDE/USB/… adapter), partition type, etc.).

Linux offers an additional possibility, which is to load an initial filesystem in RAM that's used during the boot process in order to locate and mount the root filesystem. This initial filesystem can contain modules that handle the device and filesystem type of the root filesystem. There are two slightly different mechanisms: initrd and initramfs.

Related Solutions

Linux Kernel – How to Load bzImage in QEMU

From qemu's help:

Linux/Multiboot boot specific:
-kernel bzImage use 'bzImage' as kernel image
-append cmdline use 'cmdline' as kernel command line
-initrd file    use 'file' as initial ram disk
-dtb    file    use 'file' as device tree image

A quick test here using Arch's kernel/initrd (qemu -kernel /boot/vmlinuz-linux -initrd /boot/initramfs-linux.img) worked (dropped me into a recovery shell since I didn't provide a root device).

Linux – Kernel and QEMU : Unable to mount root fs error

I don't think you would have to start debugging the kernel right away. This error message means that the kernel is unable to mount the partition you requested to be /. This would happen for example if you gave it an empty disk image (my hunch is this is your case) - the kernel in the VM sees an unpartitioned drive, there is no /dev/sda1 just /dev/sda. To overcome this follow the instructions in the guide you have used - download a bootable ISO image and use it to install system into the VM image. When raw disk image is used, it can be directly partitioned with utilities like gdisk, fdisk or parted.

Another possibility is, that there you are trying to mount a filesystem for which the kernel doesn't have a driver. This usually happens when one uses a kernel, that has most drivers in loadable modules on initrd and the initrd isn't loaded (hence the kernel lacks the ability to understand the particular filesystem).

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Linux Kernel – How to Load bzImage in QEMU

Linux – Kernel and QEMU : Unable to mount root fs error

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