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Kernel Build Management & Your System-Specific Optimization Guide

Managing Multiple Kernel Versions

Kernel Naming Strategy

The kernel version is controlled by the EXTRAVERSION variable in the Makefile and CONFIG_LOCALVERSION in your config.

Method 1: Using .config (Recommended)

cd /usr/src/linux

# Edit .config and find/add this line:
CONFIG_LOCALVERSION="-custom"

# Or use menuconfig:
make menuconfig
# Navigate to: General setup --> Local version - append to kernel release
# Enter: -custom (or -latest, -untested, etc.)

Method 2: Edit Makefile Directly

# At the top of the Makefile you'll see:
VERSION = 6
PATCHLEVEL = 12
SUBLEVEL = 6
EXTRAVERSION =

# Change EXTRAVERSION to:
EXTRAVERSION = -custom

Suggested Naming Convention

For your learning process, I recommend this progression:

  1. 6.12.6 (your current working kernel - KEEP THIS)
  2. 6.12.6-v2 (first optimization attempt)
  3. 6.12.6-v3 (further refinements)
  4. 6.12.6-stripped (when you've removed lots of stuff)
  5. 6.12.6-final (when you're happy with it)

Or use dates:

  • 6.12.6-20241220 (today's build)
  • 6.12.6-20241221 (tomorrow's build)

Complete Build Process with Versioning

cd /usr/src/linux

# 1. Set the version name
make menuconfig
# Set Local version to: -v2

# 2. Build
make -j4 2>&1 | tee build.log   # 4 cores = -j4
make modules -j4

# 3. Install (this creates versioned directories automatically)
sudo make modules_install   # Creates /lib/modules/6.12.6-v2/
sudo make install          # Creates /boot/vmlinuz-6.12.6-v2

# 4. Update bootloader
sudo update-grub           # Debian/Ubuntu
# or
sudo grub-mkconfig -o /boot/grub/grub.cfg  # Other distros

Managing Your Kernels

# List installed kernels
ls -lh /boot/vmlinuz-*
ls /lib/modules/

# Current running kernel
uname -r

# Remove old kernel (BE CAREFUL!)
sudo apt remove linux-image-6.12.6-v2   # If installed via package
# or manually:
sudo rm /boot/vmlinuz-6.12.6-v2
sudo rm /boot/initrd.img-6.12.6-v2
sudo rm /boot/config-6.12.6-v2
sudo rm /boot/System.map-6.12.6-v2
sudo rm -rf /lib/modules/6.12.6-v2/
sudo update-grub

Bootloader Management

Your GRUB menu will automatically list all kernels. To choose at boot:

  1. Reboot
  2. Press ESC/Shift during boot to see GRUB menu
  3. Select "Advanced options"
  4. Choose your kernel

To set default kernel:

# Edit /etc/default/grub
sudo nano /etc/default/grub

# Find and modify:
GRUB_DEFAULT=0              # First kernel in list
# or
GRUB_DEFAULT="Advanced options for Debian GNU/Linux>Debian GNU/Linux, with Linux 6.12.6"

# Apply changes
sudo update-grub

Your System Analysis

Based on your lspci and lsmod output, here's what you have:

Hardware Summary

  • CPU: Intel Core i5-4460 (Haswell, 4 cores, 3.2GHz base, 3.4GHz boost)
  • GPU: Intel HD Graphics (integrated, i915 driver)
  • Ethernet: Realtek RTL8111 (r8169 driver)
  • Audio: Intel HD Audio
  • Storage: SATA via Intel AHCI controller
  • USB: XHCI (USB 3.0) and EHCI (USB 2.0) controllers
  • Chipset: Intel H97
  • No WiFi, no Bluetooth, no discrete GPU

Current Kernel Issues to Address

Problem 1: Debug Symbols (BIGGEST SPACE SAVER)

# Your modules have debug info:
$ file /lib/modules/6.12.6/kernel/drivers/net/ethernet/realtek/r8169.ko
... with debug_info, not stripped

# Debian's don't:
$ file /lib/modules/6.1.0-41-amd64/kernel/drivers/net/ethernet/realtek/r8169.ko
... not stripped   (but no debug_info!)

This is why your modules are 515M vs Debian's 395M!

Fix in .config:

CONFIG_DEBUG_INFO=n
CONFIG_DEBUG_INFO_NONE=y
CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=n
CONFIG_DEBUG_KERNEL=n

Or in menuconfig:

Kernel hacking -->
  Compile-time checks and compiler options -->
    [ ] Compile the kernel with debug info  # DISABLE THIS

Problem 2: Too Many Loaded Modules (141!)

Many of these are networking/firewall modules you may not need.

System-Specific Optimization Checklist

Phase 1: Quick Wins (Do This First)

cd /usr/src/linux
cp /boot/config-6.12.6 .config
make menuconfig

General Setup

  • Set Local version: -v2
  • Kernel compression: Change to ZSTD (faster boot than XZ)
  • DISABLE: Auditing support (unless you need SELinux/AppArmor auditing)
  • Control groups: Keep (needed by systemd)
  • initramfs support: Keep enabled

Processor Type and Features

  • Processor family: Change from generic to Core 2/newer Xeon
    • Location: Processor type --> Processor family
    • Your Haswell i5 is covered by this option
  • Maximum number of CPUs: Change from 512/1024 to 4
    • You have exactly 4 cores, no hyperthreading
  • SMT (Hyperthreading): Disable (you don't have it - Model 60, 1 thread per core)
  • Preemption Model: Select Preemptible Kernel (Low-Latency Desktop)
  • Timer frequency: Select 1000 HZ
  • NUMA: Disable (single socket system)
  • DISABLE: CPU microcode loading facility (you can use fwupd in userspace instead)
  • CPU Frequency scaling: Keep enabled

Power Management

  • ACPI: Keep
  • CPU Frequency scaling: Keep
  • CPU idle: Keep
  • Suspend to RAM: Keep if you use it
  • Hibernate: Keep if you use it

Bus Options

  • PCI support: Keep
  • PCI Express hotplug: Probably disable
  • DISABLE: CardBus support
  • DISABLE: PCMCIA support

Networking

You have extensive netfilter/iptables modules loaded. If you don't run a firewall:

  • Consider disabling or building as modules:
    • Netfilter (iptables/nftables) - but keep if you use a firewall
    • Bridge support - disable unless you use VMs/containers
    • 802.1Q VLAN - disable unless needed

Keep enabled:

  • TCP/IP networking
  • Unix domain sockets
  • IPv6 (or disable if you really don't use it)

Definitely disable:

  • Amateur Radio support
  • IrDA subsystem
  • Bluetooth (you don't have it)
  • Wireless (you don't have WiFi)
  • NFC
  • Old protocols: IPX, AppleTalk, etc.

Device Drivers

Graphics
Device Drivers -->
  Graphics support -->
    [*] /dev/agpgart (AGP Support)  # Keep for Intel
    [M] Intel 8xx/9xx/G3x/G4x/HD Graphics  # i915
        [*] Enable modesetting on intel by default
        [*] Enable Intel GVT-g graphics virtualization host support  # Disable unless you use VMs

DISABLE all of these GPU drivers:

  • ATI Radeon
  • AMD GPU
  • Nouveau (NVIDIA)
  • All other GPU vendors
Storage
Device Drivers -->
  Serial ATA and Parallel ATA drivers (libata) -->
    [*] ATA ACPI Support
    [*] SATA Port Multiplier support
    [M] AHCI SATA support                    # Your SATA controller
    [M] Intel ESB, ICH, PIIX3, PIIX4 PATA/SATA support  # For Intel chipset

DISABLE:

  • All AMD SATA
  • All Marvell SATA
  • All other vendor SATA controllers
  • Old PATA/IDE drivers (unless you have IDE drives)
  • NVMe (you don't have NVMe)
Network
Device Drivers -->
  Network device support -->
    Ethernet driver support -->
      [M] Realtek devices
          [M] Realtek 8169/8168/8101/8125 gigabit ethernet support

DISABLE EVERYTHING ELSE:

  • Intel network cards
  • AMD network cards
  • Broadcom
  • Atheros
  • All wireless drivers
  • All other ethernet chipsets
Sound
Device Drivers -->
  Sound card support -->
    Advanced Linux Sound Architecture -->
      [M] Intel HD Audio
          [M] HD Audio PCI
          [M] Build HDMI/DisplayPort HD-audio codec support

DISABLE:

  • USB Audio
  • FireWire audio
  • All other sound card vendors
  • OSS emulation
USB
Device Drivers -->
  USB support -->
    [M] XHCI HCD (USB 3.0) support
    [M] EHCI HCD (USB 2.0) support
    [M] USB Mass Storage support

DISABLE:

  • OHCI (USB 1.1)
  • UHCI (USB 1.1) - unless you have really old USB devices
  • USB over IP
  • USB Gadget support
Input Devices
Device Drivers -->
  Input device support -->
    [*] Keyboards
    [*] Mice
    [M] Event interface  # evdev

You have:

  • Cooler Master keyboard (USB)
  • SteelSeries mouse (USB)

DISABLE:

  • Touchscreens
  • Tablets (unless you have drawing tablet)
  • Joysticks (unless gaming with joystick)
Hardware Monitoring

Keep sensors for your Intel chipset, disable everything else.

Filesystems

Based on your lsblk:

  • You're using ext4 (or similar)
  • No LVM visible
  • Multiple partitions

Keep:

  • ext4
  • FAT/VFAT (for EFI partition)
  • tmpfs
  • proc/sys/devtmpfs

Consider:

  • NTFS (if dual-boot with Windows)
  • ISO9660 (for reading CDs)

DISABLE:

  • Btrfs (unless you use it)
  • XFS (unless you use it)
  • JFS, ReiserFS (ancient)
  • Network filesystems (NFS, CIFS) - or build as modules
  • Most exotic filesystems

Kernel Hacking (CRITICAL FOR SIZE)

DISABLE EVERYTHING HERE for production kernel:

Kernel hacking -->
  [ ] Kernel debugging  # DISABLE
  Compile-time checks and compiler options -->
      [ ] Compile the kernel with debug info  # CRITICAL - DISABLE THIS
      [ ] Provide GDB scripts  # DISABLE
  Memory Debugging -->
      [ ] All options  # DISABLE ALL
  [ ] KGDB  # DISABLE
  [ ] Tracers  # DISABLE ALL

Keep only:

  • Magic SysRq key (for emergencies)

Phase 2: Configuration File

Here's a starting .config snippet for your next build:

# In menuconfig, make these changes:
CONFIG_LOCALVERSION="-v2"

# Processor
CONFIG_MCORE2=y                    # Core 2/newer Xeon
CONFIG_NR_CPUS=4                   # Exactly 4 cores
CONFIG_SCHED_SMT=n                 # No hyperthreading
CONFIG_PREEMPT=y                   # Low-latency desktop
CONFIG_HZ_1000=y                   # 1000 Hz timer
CONFIG_NUMA=n                      # Single socket

# Debugging - DISABLE ALL
CONFIG_DEBUG_INFO=n
CONFIG_DEBUG_INFO_NONE=y
CONFIG_DEBUG_KERNEL=n
CONFIG_KGDB=n
CONFIG_FTRACE=n

# Compression
CONFIG_KERNEL_ZSTD=y               # Fast boot

# Features you don't need
CONFIG_BT=n                        # No bluetooth
CONFIG_WLAN=n                      # No WiFi
CONFIG_PCMCIA=n                    # No PCMCIA
CONFIG_HAMRADIO=n                  # No amateur radio

Build Script

Create a helper script:

#!/bin/bash
# ~/kernel-build.sh

set -e  # Exit on error

VERSION="v2"
CORES=4

cd /usr/src/linux

echo "Building kernel version: $VERSION"
echo "Using $CORES cores"

# Build
echo "=== Building kernel ==="
time make -j${CORES} 2>&1 | tee /tmp/kernel-build.log

echo "=== Building modules ==="
time make modules -j${CORES}

echo "=== Installing modules ==="
sudo make modules_install

echo "=== Installing kernel ==="
sudo make install

echo "=== Updating bootloader ==="
sudo update-grub

echo ""
echo "✓ Build complete!"
echo "  Version: $(make kernelrelease)"
echo "  Kernel: /boot/vmlinuz-$(make kernelrelease)"
echo "  Modules: /lib/modules/$(make kernelrelease)/"
echo ""
echo "Reboot and select the new kernel from GRUB menu"

Make it executable:

chmod +x ~/kernel-build.sh

After Building

Check Size Reduction

# Compare sizes
ls -lh /boot/vmlinuz-*
du -sh /lib/modules/*

# Expected results with debug disabled:
# Modules: 515M → ~100-150M (massive reduction!)
# Kernel: Similar size or slightly smaller

Test Checklist

# After booting new kernel:
uname -r                           # Verify correct kernel
lsmod | wc -l                      # Check module count
dmesg | grep -i error              # Look for errors
dmesg | grep -i firmware           # Check firmware loading

# Test hardware:
# - Ethernet: ping 8.8.8.8
# - Sound: speaker-test -c2 -t wav
# - Graphics: glxinfo | grep -i opengl
# - USB: plug/unplug devices
# - Disk: dd if=/dev/zero of=~/test bs=1M count=100

Documentation Template

Keep notes for each build:

mkdir -p ~/kernel-builds
cat > ~/kernel-builds/6.12.6-v2.txt << 'EOF'
Build: 6.12.6-v2
Date: 2024-12-20
Based on: 6.12.6 (working)

Changes:
- Disabled debug symbols (CONFIG_DEBUG_INFO=n)
- Set processor to Core 2/newer Xeon
- Set max CPUs to 4
- Disabled SMT (no hyperthreading)
- Disabled WiFi/Bluetooth (not present)
- Disabled most other vendor network/storage drivers
- Preemption: Low-latency desktop
- Timer: 1000 Hz

Results:
- Module size: 515M → XXX M
- Boot time: [to be filled]
- Issues: [to be filled]

Status: TESTING
EOF

Next Steps

Immediate (Today/Tomorrow):

  1. Make v2 build with debug symbols disabled
  2. Test thoroughly
  3. Measure size reduction

Soon (This Week):

  1. Make v3 with hardware-specific optimizations
  2. Strip out unused drivers
  3. Fine-tune performance settings

Later (Next Week):

  1. Compare performance (boot time, responsiveness)
  2. Create final optimized config
  3. Consider upgrading to newer kernel (6.13 is coming)

Safety Tips

  1. NEVER remove the working 6.12.6 kernel until the new one is proven stable
  2. Always keep at least 2 bootable kernels
  3. Document every change before you forget why you made it
  4. Test one major change at a time
  5. Keep the previous .config as .config.backup

Recovery

If the new kernel doesn't boot:

  1. Reboot
  2. Select old kernel (6.12.6) from GRUB
  3. Review changes
  4. Try again

If GRUB menu doesn't appear:

  • Hold Shift during boot
  • Or press ESC repeatedly

Useful Commands

# Compare two configs
cd /usr/src/linux
diff .config.backup .config > changes.txt
scripts/diffconfig .config.backup .config

# Find what changed
grep "^[+-]" changes.txt

# Check if option is enabled
grep CONFIG_DEBUG_INFO .config

# See all debug options
grep -i debug .config | grep "=y"

# Current kernel config
zcat /proc/config.gz > running.config  # if CONFIG_IKCONFIG_PROC=y
# or
cat /boot/config-$(uname -r)

# Module info
modinfo i915
lsmod | grep i915

# Module dependencies
modprobe --show-depends i915

Good luck with your kernel optimization journey! 🚀