Bare Linux kernel/Busybox system displays in QEMU, not on hardware

dMeister · 11-06-2022, 02:14 PM

I'm trying to boot a bare system in the form of an ISO written on a USB drive. I compiled the kernel and Busybox, created an initramfs file with Busybox and an init script, formatted the kernel and initramfs images into an ISO, then wrote that ISO directly to the USB drive using dd. I tested the drive directly using the following command:

Code:

qemu-system-x86_64 -hda /dev/sda

It boots into GRUB and displays the one entry I created. I can select the entry, and the boot procedure begins and prints out all the log info to the screen, and eventually I get access to the shell that I spawn in the init script. If I press CTRL+D and kill the shell, the kernel goes into a panic as would be expected.

However, when I try to boot the drive directly on my PC, GRUB loads, but when I select the entry to boot, nothing is displayed. I think the kernel is booting up, because if I press CTRL+D I can see from my blinking CAPS lock key that the kernel is panicking. But nothing shows up on the screen. Any ideas as to why the drive is bootable in QEMU but not my actual PC?

Some extra details--

Linux Kernel 5.19.17
compilation commands:

Code:

make x86_64_defconfig

Code:

make

(everything else left default)

Busybox 1.34.1

Code:

make x86_64_defconfig

Enable static linking, everything else default. I'm running Manjaro which doesn't include libcrypt.a, so I downloaded it manually and copied it into my /lib directory.

Code:

make
make install

Inside the Busybox _install directory

Code:

mkdir dev proc sys

Create a file "init".

Init script:

Code:

#!/bin/sh
mount -t devtmpfs none /dev
mount -t proc none /proc
mount -t sysfs none /sys
echo  "Hello, Linux!"
exec /bin/sh

Creating initramfs.cpio.gz from the _install directory

Code:

find . -print0 | cpio --null -ov --format=newc | gzip -9 > ../initramfs.cpio.gz

To create the ISO image, inside of a directory called iso/

Code:

mkdir iso/boot iso/boot/grub
cp <kernel build dir>/boot/bzImage <Busybox build directory>/initramfs.cpio.gz .

Create a file in iso/boot/grub gruf.cfg, contents:

Code:

set default=0
set timeout=10
insmod efi_gop
insmod font
if loadfont /boot/grub/fonts/unicode.pf2
then
        insmod gfxterm
        set gfxmode=auto
        set gfxpayload=keep
        terminal_output gfxterm
fi

menuentry 'myos' --class os {
    insmod gzio
    insmod part_msdos
    linux /boot/bzImage
    initrd /boot/initramfs.cpio.gz
}

To make the ISO

Code:

grub-mkrescue -o myos.iso iso/

And finally I write myos.iso directly to /dev/sda.

zeebra · 11-12-2022, 06:13 AM

This is a very complicated question you are asking here, so many things could go wrong during such a boot. Where to even start?

Are you sure that Kernel can boot on your hardware? Can it, if you say boot it with Manjaro?

!!! · 11-12-2022, 09:19 AM

[Simple

] mll? http://DistroWatch.com/mll
http://minimal.idzona.com/the_dao_of...linux_live.txt

(It's been my lifelong dream get up the '?gumption?' to build this simple thing, so ...) (c.f.)

WILDguess (withOUT carefully reading OP):
Might you be missing the video driver for your hardware, but included the video driver for QEMU's virtual video device? (I vaguely think defconfig reads the current lsmod, or some functionally similar Magic)

dMeister · 11-23-2022, 11:42 PM

I know both my PC and laptop can run Linux because I'm currently running Manjaro on both. I think the issue is related to missing drivers, specifically Nvidia drivers, because my PC display runs on my graphics card. I tried booting the same ISO on my laptop (which has no dedicated graphics card) and the display worked, which I suppose would support that theory. Or maybe it's common knowledge that extra drivers will be needed if the system display is running from a graphics card--I'm very new to kernel tinkering of any kind.

Are there any general routes to take when trying to diagnose issues such as this? That is, debugging a kernel at early stages and boot time? As I mentioned, I'm new to this and would like to learn how to approach this in the future.