cd into a Linux kernel source tree, run one command, and get a running QEMU VM with BusyBox.

This is better: https://github.com/cirosantilli/linux-kernel-module-cheat

Based on: https://github.com/ivandavidov/minimal Merge back declined at: ivandavidov/minimal#20

Tested in Ubuntu 14.04 AMD64, QEMU 2.0.0.

sudo apt-get install git qemu sudo apt-get build-dep busybox linux-image-$(uname -r) mkdir -p ~/bin cd ~/bin git clone --recursive https://github.com/cirosantilli/runlinux echo 'PATH="$PATH:'$(pwd)'/runlinux"' >> ~/.bashrc . ~/.bashrc 

git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git cd linux git checkout v4.2 runlinux 

It takes a while the first time because things have to be built, but later runs will be faster.

Then hack the kernel source to your liking, and run:

runlinux 

again to try it out.

Out-of-tree build with custom configuration:

export KBUILD_OUTPUT="$(pwd)/../build" make menuconfig runlinux 

If an existing configuration is not found at KBUILD_OUTPUT, make defconfig is used. If found, it is used and left untouched.

Pass extra options to QEMU:

runlinux -- -bios ~/path/to/OVMF.fd 

This for example uses the OVMF UEFI X64 r15214 instead of the default BIOS.

Generate a main.img file in your build directory:

runlinux -i 

Insert an USB and determine its device (/dev/sdX):

sudo lsblk sudo fdisk -l 

Burn the image to the USB:

sudo dd if=main.img of=/dev/sdX 

Then:

• insert the USB in a computer
• during boot, hit some special hardware dependant key, usually F12, Esc
• choose to boot from the USB

You can also ensure that the image works fine with:

qemu-system-x86_64 -enable-kvm -hda main.img 

Tested on: ThinkPad T400.

If you just want to run your own root filesystem and ignore BusyBox completely, use:

runlinux -n /path/to/my/directory/ runlinux -n /path/to/my/init 

If you pass it:

• a directory, the directory will be packed into a filesystem.

  The first thing that Linux runs is the /init executable of that directory. You usually want that to be an executable without dependencies that never exits.

• a file, it will be renamed to init and put at the root of the packed filesystem.

See this SO answer for more details on how to create your own simple initrd.

TODO this is currently broken: https://sourceware.org/bugzilla/show_bug.cgi?id=13984 but I've since found the workaround and just need to stop being lazy and implement it: http://stackoverflow.com/questions/11408041/how-to-debug-the-linux-kernel-with-gdb-and-qemu/33203642#33203642

Debug the kernel on GDB:

../runlinux/runlinux -g 

This will set the CONFIG_DEBUG_INFO configuration and rebuild the kernel if necessary.

It runs QEMU on the background of the current shell, and opens GDB there.

You are now ready to debug, e.g.:

# Has to be hardware breakpoint. TODO why https://bugs.launchpad.net/ubuntu/+source/qemu-kvm/+bug/901944/comments/12 hbreak start_kernel list continue