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Adds barebone linux compilation iso #6

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16 changes: 16 additions & 0 deletions linux-from-kernel-scratch/Dockerfile
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FROM --platform=linux/amd64 ubuntu:22.04

ENV DEBIAN_FRONTEND=noninteractive

RUN apt-get update && apt-get install -y \
git vim make gcc libncurses-dev flex bison bc cpio \
libelf-dev libssl-dev syslinux isolinux dosfstools \
xorriso mtools grub-pc-bin grub-efi-amd64-bin bzip2 \
&& rm -rf /var/lib/apt/lists/*

WORKDIR /build

COPY build.sh /build/
RUN chmod +x /build/build.sh

CMD ["/build/build.sh"]
45 changes: 45 additions & 0 deletions linux-from-kernel-scratch/README.md
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# Minimal Linux Distro

A bootable x86_64 Linux ISO built from scratch using Docker.

## What's Inside

- **Linux Kernel** - Latest mainline kernel (defconfig)
- **BusyBox** - Static userspace with common utilities
- **ISOLINUX** - Bootloader

## Files

```
├── Dockerfile # x86_64 Ubuntu build environment
├── build.sh # Full build (kernel + busybox + iso)
├── build-busybox-iso.sh # Partial build (reuses existing kernel)
└── output/
├── bzImage # Compiled kernel
├── initramfs.gz # Root filesystem
└── minimal-linux.iso # Bootable ISO (16MB)
```

## Build

```bash
# Build Docker image
docker build --platform linux/amd64 -t linux-builder .

# Full build (~25 min on ARM Mac)
docker run --platform linux/amd64 --rm -v "$(pwd)/output:/output" linux-builder

# If kernel exists, build only busybox + iso (~3 min)
docker run --platform linux/amd64 --rm \
-v "$(pwd)/output:/output" \
-v "$(pwd)/build-busybox-iso.sh:/build/build-busybox-iso.sh" \
linux-builder bash /build/build-busybox-iso.sh
```

## Test

```bash
qemu-system-x86_64 -cdrom output/minimal-linux.iso -m 512
```

Boots to a shell with `ls`, `vi`, `grep`, `awk`, `sed`, `bc`, and more.
81 changes: 81 additions & 0 deletions linux-from-kernel-scratch/build-busybox-iso.sh
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#!/bin/bash
set -e

echo "=== Building BusyBox and ISO (kernel already built) ==="

# Check kernel exists
if [ ! -f /output/bzImage ]; then
echo "ERROR: bzImage not found in /output"
exit 1
fi
echo ">>> Found existing kernel: $(ls -lh /output/bzImage | awk '{print $5}')"

# Build BusyBox
echo ">>> Cloning BusyBox from GitHub mirror..."
git clone --depth 1 https://github.com/mirror/busybox.git busybox
cd busybox

echo ">>> Configuring BusyBox (static build)..."
make defconfig
sed -i 's/# CONFIG_STATIC is not set/CONFIG_STATIC=y/' .config
make oldconfig

echo ">>> Building BusyBox..."
make -j$(nproc) 2>&1 | tail -5

mkdir -p /output/initramfs
make CONFIG_PREFIX=/output/initramfs install
cd ..

# Create init script
echo ">>> Creating init script..."
cd /output/initramfs
cat > init << 'INITEOF'
#!/bin/sh
mount -t proc none /proc
mount -t sysfs none /sys
mount -t devtmpfs none /dev

echo "Welcome to Minimal Linux!"
echo "Type 'poweroff' to shutdown."
echo ""

exec /bin/sh
INITEOF
chmod +x init
mkdir -p proc sys dev

# Create initramfs
echo ">>> Creating initramfs..."
find . | cpio -o -H newc 2>/dev/null | gzip > /output/initramfs.gz
cd /output

# Create ISO
echo ">>> Creating bootable ISO..."
mkdir -p iso/boot/isolinux

cp /usr/lib/ISOLINUX/isolinux.bin iso/boot/isolinux/
cp /usr/lib/syslinux/modules/bios/ldlinux.c32 iso/boot/isolinux/
cp bzImage iso/boot/
cp initramfs.gz iso/boot/

cat > iso/boot/isolinux/isolinux.cfg << 'CFGEOF'
DEFAULT linux
LABEL linux
KERNEL /boot/bzImage
APPEND initrd=/boot/initramfs.gz
CFGEOF

xorriso -as mkisofs \
-o /output/minimal-linux.iso \
-b boot/isolinux/isolinux.bin \
-c boot/isolinux/boot.cat \
-no-emul-boot \
-boot-load-size 4 \
-boot-info-table \
-isohybrid-mbr /usr/lib/ISOLINUX/isohdpfx.bin \
iso/

echo ""
echo "=== BUILD COMPLETE ==="
ls -lh /output/minimal-linux.iso
100 changes: 100 additions & 0 deletions linux-from-kernel-scratch/build.sh
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#!/bin/bash
set -e

echo "=== Building Minimal Linux Distro ==="

# 1. Build Linux Kernel (minimal config for faster build)
echo ">>> Cloning Linux kernel..."
git clone --depth 1 https://github.com/torvalds/linux.git
cd linux

echo ">>> Configuring kernel (minimal x86_64)..."
make defconfig
# Enable initramfs support
scripts/config --enable CONFIG_BLK_DEV_INITRD
scripts/config --enable CONFIG_RD_GZIP
scripts/config --enable CONFIG_RD_BZIP2
scripts/config --enable CONFIG_RD_LZMA
scripts/config --enable CONFIG_RD_XZ
scripts/config --enable CONFIG_RD_LZO
scripts/config --enable CONFIG_RD_LZ4
scripts/config --enable CONFIG_RD_ZSTD
make olddefconfig

echo ">>> Building kernel (this takes a while)..."
make -j$(nproc) bzImage 2>&1 | tail -20

mkdir -p /output
cp arch/x86/boot/bzImage /output/
cd ..

# 2. Build BusyBox
echo ">>> Cloning BusyBox..."
git clone --depth 1 https://github.com/mirror/busybox.git busybox
cd busybox

echo ">>> Configuring BusyBox (static build)..."
make defconfig
sed -i 's/# CONFIG_STATIC is not set/CONFIG_STATIC=y/' .config
make oldconfig

echo ">>> Building BusyBox..."
make -j$(nproc) 2>&1 | tail -10

mkdir -p /output/initramfs
make CONFIG_PREFIX=/output/initramfs install
cd ..

# 3. Create init script
echo ">>> Creating init script..."
cd /output/initramfs
cat > init << 'INITEOF'
#!/bin/sh
mount -t proc none /proc
mount -t sysfs none /sys
mount -t devtmpfs none /dev

echo "Welcome to Minimal Linux!"
echo "Type 'poweroff' to shutdown."
echo ""

exec /bin/sh
INITEOF
chmod +x init
mkdir -p proc sys dev

# 4. Create initramfs
echo ">>> Creating initramfs..."
find . | cpio -o -H newc 2>/dev/null | gzip > /output/initramfs.gz
cd /output

# 5. Create ISO with ISOLINUX
echo ">>> Creating bootable ISO..."
mkdir -p iso/boot/isolinux

cp /usr/lib/ISOLINUX/isolinux.bin iso/boot/isolinux/
cp /usr/lib/syslinux/modules/bios/ldlinux.c32 iso/boot/isolinux/
cp bzImage iso/boot/
cp initramfs.gz iso/boot/

cat > iso/boot/isolinux/isolinux.cfg << 'CFGEOF'
DEFAULT linux
LABEL linux
KERNEL /boot/bzImage
APPEND initrd=/boot/initramfs.gz
CFGEOF

xorriso -as mkisofs \
-o /output/minimal-linux.iso \
-b boot/isolinux/isolinux.bin \
-c boot/isolinux/boot.cat \
-no-emul-boot \
-boot-load-size 4 \
-boot-info-table \
-isohybrid-mbr /usr/lib/ISOLINUX/isohdpfx.bin \
iso/

echo ""
echo "=== BUILD COMPLETE ==="
ls -lh /output/minimal-linux.iso
echo "ISO ready at /output/minimal-linux.iso"
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