This is quick guide to compile linux kernel and minimal boot in Qemu.
Compiling linux kernel Link to heading
To compile linux kernel, you will need .config to configure the build. To generate default .config:
make defconfig
if you are planning to upgrade the kernel version on your machine, you need to use the current config to generate compatible configuration
cp /boot/config-`kernel version` ./config
make oldconfig
Creating busybox initramfs Link to heading
mkinitramfs creates minimal busybox file system with busybox unix commands.
More importantly, the kernel will try to mount root file system by default.So, you will get kernel panic if kernel didn’t find one.
mkinitramfs -o initrd.img
Booting qemu Link to heading
Using qemu-system-x86_64 which is vanilla qemu (No KVM)
qemu-system-x86_64 -kernel ./arch/x86_64/boot/bzImage -initrd initrd.img -m 2048 -nographic -append "console=ttyS0"
After boot messages, you should see something like:
[ 5.916979] ata_id (1021) used greatest stack depth: 14128 bytes left
...
...
BusyBox v1.27.2 (Ubuntu 1:1.27.2-2ubuntu3.2) built-in shell (ash)
Enter 'help' for a list of built-in commands.
(initramfs) uname -a
Linux (none) 4.15.0-rc6+ #12 SMP Sat May 11 11:09:29 EET 2019 x86_64 GNU/Linux
Moving between console and qemu monitor Link to heading
To reboot qemu, you can move to qemu monitor by Ctrl-a then c