Linux Kernel Info

Distro	Action	Update initramfs	Update DKMS	GRUB Update
Ubuntu	update with apt	triggered	triggered	triggered
Ubuntu	update with mainline	manual	manual	triggered
Ubuntu	manual download dpkg	triggered	manual	triggered
Ubuntu	custom build - versioned	manual ( usually )	manual	manual
Ubuntu	custom build - git cloned	manual	manual	manual
Arch	update with pacman	triggered	manual	triggered
Arch	custom build - versioned	manual	manual	manual
Arch	custom build - git cloned	manual	manual	manual

Ubuntu - Upgrade Kernel

Using apt:

uname -r
sudo apt update && sudo apt upgrade
apt list --upgradable | grep linux-image        # check available kernels
sudo apt install --install-recommends linux-generic  # upgrade to latest kenel
sudo reboot
uname -r

• DKMS module update is triggered automatically when using apt on Ubuntu

Install Latest Mainline Kernel (Bleeding Edge):

sudo add-apt-repository ppa:cappelikan/ppa
sudo apt update
sudo apt install mainline
mainline --list
mainline --install v6.6.1
mainline-gtk               # or use GUI
sudo reboot
uname -r

Update initramfs and DKMS modules for this kernel version:

sudo update-initramfs -c -k 6.6.1

sudo dkms autoinstall -k 6.6.1
dkms status

Manual download ( https://kernel.ubuntu.com/~kernel-ppa/mainline/ ):

wet https://kernel.ubuntu.com/~kernel-ppa/mainline/v6.6.1/amd64/linux-image-6.6.1-xxxx.deb
wget https://kernel.ubuntu.com/~kernel-ppa/mainline/v6.6.1/amd64/linux-headers-6.6.1-xxxx.deb

sudo dpkg -i linux-*.deb
sudo reboot
uname -r

Update DKMS modules for this kernel version:

sudo dkms autoinstall -k 6.6.1
dkms status

Ubuntu - Compile Kernel

uname -r

sudo apt update && sudo apt upgrade -y
sudo apt install -y build-essential libncurses-dev bison flex libssl-dev libelf-dev bc

Download from Kernel.org (Recommended for Latest Kernel)

cd /usr/src
sudo wget https://cdn.kernel.org/pub/linux/kernel/v6.x/linux-6.6.1.tar.xz
sudo tar -xf linux-6.6.1.tar.xz
cd linux-6.6.1

Get Ubuntu’s Kernel Source (More Stable)

sudo apt install -y git fakeroot
git clone git://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/mainline linux-source
cd linux-source

cat Makefile | grep -E '^VERSION|^PATCHLEVEL|^SUBLEVEL'   # grab kernel version for this latest cloned source
git describe --tags                                       # could also use this if it has tags

Configure:

cp -v /boot/config-$(uname -r) .config # copy old config if using it

make olddefconfig     # Uses old config, applies default values for any new options introduced in the newer kernel version.
make oldconfig        # Uses old config but asks about new options.
make defconfig        # Uses a default minimal config.
make menuconfig       # use interactive menu
make tinyconfig       # minimal config

Can use these together:

make olddefconfig       # get a good config to start
make menuconfig         # customize it

Build:

make -j$(nproc)

Install:

sudo make modules_install
sudo make install

Create new initramfs, update DKMS modules, update GRUB, and reboot:

sudo update-initramfs -c -k 6.6.1
sudo dkms autoinstall -k 6.6.1
sudo update-grub
sudo reboot

Verify:

uname -r

Remove old kernels if you want:

sudo apt remove --purge linux-image-<old-version>
sudo update-grub

Arch Linux - Upgrade Kernel

Use Pacman:

uname -r

sudo pacman -Syu                             # update entire system including kernel

sudo pacman -S linux linux-headers            # update just the kernel and headers
sudo pacman -S linux-lts linux-lts-headers    # for LTS kernel

sudo dkms autoinstall                         # rebuild DKMS modules if used ( need to do manually )

sudo grub-mkconfig -o /boot/grub/grub.cfg     # update grub ( usually automatic but do anyway )

sudo reboot
uname -r

Arch Linux - Compile Kernel

uname -r

sudo pacman -Syu --needed base-devel bc kmod cpio flex bison libelf pahole git

latest stable:

cd /usr/src
sudo git clone --depth=1 https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
cd linux

cat Makefile | grep -E '^VERSION|^PATCHLEVEL|^SUBLEVEL'   # grab kernel version for this latest cloned source
git describe --tags                                       # could also use this if it has tags

OR specific version:

sudo wget https://cdn.kernel.org/pub/linux/kernel/v6.x/linux-6.7.tar.xz
sudo tar -xvf linux-6.7.tar.xz
cd linux-6.7

Use current kernel’s config as a base:

zcat /proc/config.gz > .config

make olddefconfig     # Uses old config, applies default values for any new options introduced in the newer kernel version.
make oldconfig        # Uses old config but asks about new options.
make defconfig        # Uses a default minimal config.
make menuconfig       # use interactive menu
make tinyconfig       # minimal config

Can use these together:

make olddefconfig       # get a good config to start
make menuconfig         # customize it

Build:

make -j$(nproc)

Install:

make modules_install
sudo make install

• The kernel image (/boot/vmlinuz-linux)
• The system map (/boot/System.map)
• The configuration (/boot/config)

Update the initramfs, update DKMS modules, update GRUB, and reboot:

sudo mkinitcpio -P
sudo dkms autoinstall
sudo grub-mkconfig -o /boot/grub/grub.cfg
sudo reboot

Reboot:

uname -r

Kernel Configuration Options – Common settings for a custom kernel

Types of options/parameters:

• Kernel Configuration Options - They control which features and modules are included in the kernel binary.
• Sysctl Parameters - Used for adjusting kernel behavior at runtime.
• Kernel Command Line Parameters - Configure the kernel during the boot process. Passed by bootloader and can’t be changed at runtime.

CPU and More

Some CPU settings:

CONFIG_SCHED_CORE=y         # Enable Multi-core Scheduling - Improves performance in multi-threaded workloads.
CONFIG_HZ_1000=y            # High Timer Frequency - Increase timer tick rate to 1000Hz for finer time granularity
CONFIG_NO_HZ=n              # Disable Dynamic Ticks (NO_HZ) - Ensures consistent CPU cycles by avoiding tickless idle states
CONFIG_CPU_FREQ=n           # Disable CPU Frequency Scaling to lock CPU speed to max performance
CONFIG_PM_ADVANCED_DEBUG=n  # Disables power debugging features to save CPU cycles

Fully Preemptible Kernel (RT)

• Set to “Preempt-RT” for hard real-time behavior
• Ensures minimum jitter in response times.
• Reduces context-switching delays.
• real-time tasks can interrupt lower-priority or non-real-time tasks without significant delay

CONFIG_PREEMPT_RT_FULL=y    # full real time patchs for max RT performance
CONFIG_PREEMPT_RT=y         # enable real time premption
CONFIG_PREEMPT_VOLUNTARY=y  # only voluntary premption
CONFIG_PREEMPT=y            # General preemption without full real-time guarantees

Memory Management Tweaks

Swappiness

CONFIG_SWAP=n     Disable Swappiness

• don’t swap unless necessary
• Reduces reliance on swap memory if you have enough RAM.
• may use OOM Killer instead of swapping
• may fail to allocate memory and crash

Enable HugePages / Transparent Huge Pages (THP)

CONFIG_TRANSPARENT_HUGEPAGE=y

Configure in runtime:

echo always > /sys/kernel/mm/transparent_hugepage/enabled

Transparent Huge Pages (THP)

• Prob improve performance if you have the mem, can cause issues if you don’t.
• Reduces TLB misses, improving memory access speed.
• Pages will be 2MB or higher instead of standard 4kb
• Great for things that use a lot of memory
• Great for databases, VMs and containerized environments
• May cause (or avoid) memory fragmentation
• Might negatively affect latency-sensitive applications
• Can waste memory
• Excessive compaction when searching for pages can increase CPU usage
• Managed by OS

Huge Pages

• Managed by application

Network

Distributes network packets across CPU cores to reduce bottlenecks.

CONFIG_RPS=y    # Receive Packet Steering (RPS) - distribute packets to mulitple CPU cores
CONFIG_RFS=y    # Receive Flow Steering (RFS) - match to core with relevant app

CONFIG_NETWORK_PHY_TIMESTAMPING=y   # Enable High-Resolution Timestamps for precise latency measurements

Kernel IO Scheduler

Enable schedulers:

CONFIG_IOSCHED_DEADLINE=y         # enable deadline IO scheduler, Avoid CFQ, which prioritizes fairness over speed. For time-sensitive applications and predictable I/O.
CONFIG_IOSCHED_NOOP=y
CONFIG_IOSCHED_CFQ=y
CONFIG_MQ_IOSCHED_DEADLINE=y      # when Multi-Queue Block I/O Layer (blk-mq) is enabled ( default for new systems )
CONFIG_MQ_IOSCHED_KYBER=y
CONFIG_MQ_IOSCHED_BFQ=y

CONFIG_DEFAULT_IOSCHED="noop"     # change default ( for Single-Queue NOT blk-mq )

Change default IO scheduler for blk-mq ( kernel param, can’t do at compile time ):

/etc/default/grub



GRUB_CMDLINE_LINUX="elevator=mq-deadline"        #

For Legacy Block Layer (Single-Queue)

• noop - A simple, minimal I/O scheduler that passes requests directly with no reordering. Ideal for SSDs or virtualized environments.
• deadline - Prioritizes I/O requests with deadlines to prevent starvation. Good for latency-sensitive applications.
• cfq - (Completely Fair Queuing) Provides fairness across processes and is often used for traditional HDDs. Prioritizes fairness over raw performance.

For Multi-Queue Block Layer (blk-mq)

• mq-deadline - The multi-queue version of the Deadline scheduler. Maintains low latency while ensuring fairness.
• kyber - A lightweight I/O scheduler designed for fast storage devices (e.g., NVMe SSDs). Focuses on low latency and throughput.
• bfq - (Budget Fair Queueing) Provides strict bandwidth and latency guarantees. Best suited for desktop or interactive workloads.
• none - Disables any scheduling. Often used for devices where hardware handles I/O management, like some RAID controllers.

Disk

CONFIG_NVME_MULTIPATH=y     # For enterprise SSDs

Security Enhancements

CONFIG_STACKPROTECTOR_STRONG=y   # Enable StackProtector, Hardens against buffer overflow attacks.
CONFIG_SECURITY_APPARMOR=y       # Enable AppArmor
CONFIG_SECURITY_SELINUX=y        # Enable SELinux
CONFIG_HARDENED_USERCOPY=y       # Enable Hardened Usercopy

Reducing Bloat (Minimal Kernel)

• Disable Unused Features
• Remove unused filesystems (Btrfs, XFS, NTFS, ReiserFS if using only ext4).
• Disable unnecessary drivers (Bluetooth, Sound, USB, Legacy Hardware).
• Disable Support for Legacy Hardware
• Remove Old CPU architectures (i386, MIPS, etc.).

CONFIG_BLK_DEV_FD=n    # remove floppy disk support
CONFIG_DEBUG_KERNEL=n  # disable debugging
CONFIG_DEBUG_INFO=n    # disable debugging
CONFIG_KGDB=n          # disable kernel debugger