lenovo-gentoo/scripts/build-kernel.sh

#!/bin/bash
set -e  # Exit on any error

# Kernel Build Script for Gentoo
# This script manually builds the kernel without using genkernel
# Date: 2025-11-05

# Configuration
KERNEL_VERSION="6.12.41-gentoo-x86_64"
KERNEL_SRC="/usr/src/linux"
LOG_DIR="/home/alexander/repository/git.hinrichs.dev/alexander/claude/gentoo-setup/logs"
TIMESTAMP=$(date +%Y%m%d-%H%M%S)
BUILD_LOG="${LOG_DIR}/kernel-build-${TIMESTAMP}.log"
CPU_CORES=16

# Colors for output
RED='\033[0;31m'
GREEN='\033[0;32m'
YELLOW='\033[1;33m'
NC='\033[0m' # No Color

log() {
    echo -e "${GREEN}[$(date '+%Y-%m-%d %H:%M:%S')]${NC} $1" | tee -a "$BUILD_LOG"
}

error() {
    echo -e "${RED}[$(date '+%Y-%m-%d %H:%M:%S')] ERROR:${NC} $1" | tee -a "$BUILD_LOG"
    exit 1
}

warning() {
    echo -e "${YELLOW}[$(date '+%Y-%m-%d %H:%M:%S')] WARNING:${NC} $1" | tee -a "$BUILD_LOG"
}

# Check if running as root
if [ "$EUID" -ne 0 ]; then
    error "This script must be run as root (use sudo)"
fi

# Create log directory if it doesn't exist
mkdir -p "$LOG_DIR"

log "=== Kernel Build Started ==="
log "Kernel Version: $KERNEL_VERSION"
log "Source Directory: $KERNEL_SRC"
log "Build Log: $BUILD_LOG"

# Step 1: Navigate to kernel source
cd "$KERNEL_SRC" || error "Failed to change to $KERNEL_SRC"
log "Changed to kernel source directory"

# Step 2: Backup current config
log "Backing up current .config to .config.backup"
if [ -f .config ]; then
    cp .config .config.backup || error "Failed to backup .config"
    log "Config backed up successfully"
else
    error "No .config file found in $KERNEL_SRC"
fi

# Step 3: Run make mrproper (clean everything)
log "Running make mrproper (cleaning build tree)..."
make mrproper >> "$BUILD_LOG" 2>&1 || error "make mrproper failed"
log "Build tree cleaned"

# Step 4: Restore config from backup
log "Restoring .config from backup"
cp .config.backup .config || error "Failed to restore .config"
log "Config restored successfully"

# Step 5: Run make oldconfig (handle any new options)
log "Running make oldconfig (updating config for new options)..."
yes "" | make oldconfig >> "$BUILD_LOG" 2>&1 || error "make oldconfig failed"
log "Config updated"

# Step 6: Build the kernel
log "Building kernel with -j${CPU_CORES}..."
log "This may take several minutes..."
make -j${CPU_CORES} >> "$BUILD_LOG" 2>&1 || error "Kernel build failed"
log "Kernel built successfully"

# Step 7: Install kernel modules
log "Installing kernel modules..."
make modules_install >> "$BUILD_LOG" 2>&1 || error "Module installation failed"
log "Modules installed to /lib/modules/${KERNEL_VERSION}"

# Step 8: Backup old kernel files
log "Creating backups of old kernel files in /boot"
BACKUP_SUFFIX="backup-${TIMESTAMP}"

if [ -f /boot/vmlinuz-${KERNEL_VERSION} ]; then
    cp /boot/vmlinuz-${KERNEL_VERSION} /boot/vmlinuz-${KERNEL_VERSION}.${BACKUP_SUFFIX}
    log "Backed up vmlinuz to vmlinuz-${KERNEL_VERSION}.${BACKUP_SUFFIX}"
fi

if [ -f /boot/System.map-${KERNEL_VERSION} ]; then
    cp /boot/System.map-${KERNEL_VERSION} /boot/System.map-${KERNEL_VERSION}.${BACKUP_SUFFIX}
    log "Backed up System.map to System.map-${KERNEL_VERSION}.${BACKUP_SUFFIX}"
fi

if [ -f /boot/initramfs-${KERNEL_VERSION}.img ]; then
    cp /boot/initramfs-${KERNEL_VERSION}.img /boot/initramfs-${KERNEL_VERSION}.img.${BACKUP_SUFFIX}
    log "Backed up initramfs to initramfs-${KERNEL_VERSION}.img.${BACKUP_SUFFIX}"
fi

# Step 9: Copy new kernel to /boot
log "Copying new kernel to /boot/vmlinuz-${KERNEL_VERSION}"
cp arch/x86_64/boot/bzImage /boot/vmlinuz-${KERNEL_VERSION} || error "Failed to copy kernel"
log "Kernel copied successfully"

# Step 10: Copy System.map
log "Copying System.map to /boot/System.map-${KERNEL_VERSION}"
cp System.map /boot/System.map-${KERNEL_VERSION} || error "Failed to copy System.map"
log "System.map copied successfully"

# Step 11: Generate initramfs with dracut
log "Generating initramfs with dracut..."
dracut --force --kver ${KERNEL_VERSION} /boot/initramfs-${KERNEL_VERSION}.img >> "$BUILD_LOG" 2>&1 || error "dracut failed"
log "Initramfs generated successfully"

# Step 12: Update GRUB
log "Updating GRUB configuration..."
grub-mkconfig -o /boot/grub/grub.cfg >> "$BUILD_LOG" 2>&1 || error "GRUB update failed"
log "GRUB updated successfully"

# Step 13: Verify files exist
log "Verifying kernel files in /boot..."
if [ ! -f /boot/vmlinuz-${KERNEL_VERSION} ]; then
    error "vmlinuz-${KERNEL_VERSION} not found in /boot"
fi
if [ ! -f /boot/System.map-${KERNEL_VERSION} ]; then
    error "System.map-${KERNEL_VERSION} not found in /boot"
fi
if [ ! -f /boot/initramfs-${KERNEL_VERSION}.img ]; then
    error "initramfs-${KERNEL_VERSION}.img not found in /boot"
fi
log "All kernel files verified"

# Summary
log "=== Kernel Build Completed Successfully ==="
log "Kernel: /boot/vmlinuz-${KERNEL_VERSION}"
log "System.map: /boot/System.map-${KERNEL_VERSION}"
log "Initramfs: /boot/initramfs-${KERNEL_VERSION}.img"
log "Modules: /lib/modules/${KERNEL_VERSION}"
log "Build log: ${BUILD_LOG}"
log ""
log "Next steps:"
log "1. Review the build log for any warnings"
log "2. Reboot the system: sudo reboot"
log "3. After reboot, verify kernel version: uname -r"
log ""
warning "Don't forget to reboot to load the new kernel!"