QEMU Setup

Install Dependency package

sudo apt update

sudo apt install -y build-essential git bc bison flex libssl-dev libelf-dev

sudo apt install -y cpio rsync file wget unzip qemu-system-x86 qemu-utils

sudo apt install -y qemu-system-gui qemu-system-common qemu-system-data

sudo apt install -y libncurses-dev python3

Create a workspace

mkdir -p ~/kernel-lab
cd ~/kernel-lab

Download Buildroot

cd ~/kernel-lab

git clone https://github.com/buildroot/buildroot.git

or use a stable release:

wget https://buildroot.org/downloads/buildroot-2026.02.tar.gz
tar xf buildroot-2026.02.tar.gz
mv buildroot-2026.02 buildroot

Configure buildroot

cd buildroot
make qemu_x86_64_defconfig

Add custome config

make menuconfig

Enable Qemu VFS

Host utilities  ---> 
    [*] host qemu
         [*] Virtual filesystem support

Enable SSH

Target packages  ---> 
    Networking applications  --->
         [*] dropbear

Save and Exit.

Enable the 9P client support in the Linux kernel.

This support need to be added with kernel, so open kernel menuconfig

make linux-menuconfig

make following changes

[*] Networking support  --->
    <*>   Plan 9 Resource Sharing Support (9P2000)  --->
        <*>   9P FD Transport (NEW)
        <*>   9P Virtio Transport

File systems  --->
    [*] Network File Systems  --->
        <*>   Plan 9 Resource Sharing Support (9P2000)
        [*]     9P POSIX Access Control Lists
        [*]     9P Security Labels

Save and Exit.

Compile buildroot

make -j$(nproc)

NOTE: it will take approx 30min to 1 hours to build depending on your system configuration.

check output

After a successful build, you'll have a new directory: output/

inside it:

output/
├── build/
├── host/
├── images/
├── staging/
└── target/

Here's what they contain:

build/ – Temporary build directories for each package.

host/ – Tools built for your Ubuntu host (including the cross-compiler if Buildroot builds one).

target/ – The target root filesystem before it's packaged.

images/ – The final bootable kernel and root filesystem images.

boot linux on qemu

bydefault, buildroot will generate a script to boot images on qemu, so we need to just run the script

./output/images/start-qemu.sh

after runnung, you will see linux booting logs on qemu and finaly

Now type root to login.

Configure

set password

bydefault there are no password for root user so lets set a password, i will suggest to use root as password to avoid confusion.

on linux qemu terminal, type passwd and then type root and press enter, again it will as for password so type root and then press enter.

enable hostfwd

so for ssh login to linux running on qemu, we need to enable some configuration.

so modify ./output/images/start-qemu.sh and make below changes

-net nic,model=virtio -net user,hostfwd=tcp::2222-:22  ${EXTRA_ARGS} "$@"

-virtfs local,path=/media/vishal/data/qemu/modules,mount_tag=hostshare,security_model=none,id=hostshare

NOTE: change /media/vishal/data/qemu/modules based on your host shared directopry path.

ssh root@localhost -p 2222

Exit from qemu

poweroff

If you want the shared folder to be mounted automatically when the guest boots,

mkdir -p /mnt/host

and add below entry to /etc/fstab

hostshare  /mnt/host  9p  trans=virtio,version=9p2000.L,_netdev  0  0

Importent location

Linux kernel source code: output/build/linux-/