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kernel-from-source.md

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Run the VM

  1. Run with Qemu. (keep inline, new lines does not work in windows terminal)

    • Create virtual disk - 'qcow2', 'raw' or other format supported by Qemu (35 GB atleast).
    qemu-system-x86_64
-accel whpx
-drive file='Ubuntu Server.qcow2,format=qcow2',if=virtio,discard=unmap
-cdrom ubuntu-server.iso
-m 8G
-smp 10
-netdev user,id=net0,hostfwd=tcp::2222-:22
-device virtio-net,netdev=net0
-vga virtio
-boot order=c
-nographic
-monitor telnet:127.0.0.1:4444,server,nowait

  2. SSH into the VM. (enable SSH via optional-features)

    ssh -p 2222 username@localhost

Setup Linux Kernel

  1. Clone the Linux kernel.

    git clone https://kernel.googlesource.com/pub/scm/linux/kernel/git/torvalds/linux

    | I thought it would be faster to download from google rather than github —less traffic, maybe? Who knows? :p

  2. Copy the source code (optional, to avoid re-downloading if something is misconfigured badly).

    mv linux linux-base
cp -r linux-base linux
cd linux

  3. Uncomment the deb-src lines and update package lists.

    vim /etc/apt/sources.list
sudo apt update

    On Ubuntu, edit /etc/apt/sources.list.d/ubuntu.sources instead:

    vim /etc/apt/sources.list.d/ubuntu.sources

  4. Enable source repositories (if missing).

    vi /etc/apt/sources.list.d/ubuntu.sources

    Add the following if it's missing:

    Types: deb deb-src
URIs: http://archive.ubuntu.com/ubuntu
Suites: noble noble-updates noble-security
Components: main restricted universe multiverse

    Update package lists and install kernel build deps:

    sudo apt update
sudo apt build-dep linux

  5. Install additional deps.

    sudo apt install libncurses-dev gawk flex bison openssl libssl-dev dkms libelf-dev libudev-dev libpci-dev libiberty-dev autoconf llvm

  6. Use the current kernel's configuration as a starting point.

    cat /boot/config-$(uname -r) > .config

  7. Configure the kernel using menuconfig.

    make menuconfig
    • Navigate to General setup →
    • Select to save the configuration.
    • Select .

    Remove Debian-specific configurations:

    • Go to Cryptographic API → Certificates for signature checking.

    • Remove debian/canonical-certs.pem from:

      (debian/canonical-certs.pem) Additional X.509 keys for default system keyring

      Change it to:

      () Additional X.509 keys for default system keyring

    • Remove debian/canonical-revoked-certs.pem from:

      (debian/canonical-revoked-certs.pem) X.509 certificates to be preloaded into the system blacklist keyring

      Change it to:

      () X.509 certificates to be preloaded into the system blacklist keyring

    • Save and Exit.

  8. Build the kernel.

    make -j$(nproc)
    • -j$(nproc): Uses all CPU cores for faster compilation.

    Install stripped kernel modules:

    sudo make INSTALL_MOD_STRIP=1 modules_install

  9. Buildroot (optional)

    • Create 'ext2' image with buildroot.

  10. Run the kernel in VM.

qemu-system-x86_64 -kernel linux/arch/x86/boot/bzImage -drive file=buildroot/output/images/rootfs.ext2,format=raw -append "root=/dev/sda console=ttyS0" -nographic -no-reboot