Managing Kernel and Modules

1. Viewing Loaded Modules

Command Description Example Output

lsmod

Lists all currently loaded kernel modules

Command	Description	Example Output
lsmod	Lists all currently loaded kernel modules	`Module Size Used by snd_hda_intel 57344 1 snd_hda_codec 139264 1 snd_hda_core 81920 2`
cat /proc/modules	Displays loaded modules with additional details like size and reference count	`snd_hda_intel 57344 1 - Live 0x0000000000000000 snd_hda_codec 139264 1 - Live 0x0000000000000000 snd_hda_core 81920 2 - Live 0x0000000000000000`
modinfo <module_name>	Shows metadata and details about a specific module	`filename: /lib/modules/5.15.0-1027-oem/kernel/sound/pci/hda/snd-hda-intel.ko alias: pci:v00008086d00002668svsdbcsci* version: 1.0.0 license: GPL`

Module                  Size  Used by
snd_hda_intel          57344  1
snd_hda_codec         139264  1
snd_hda_core           81920  2

cat /proc/modules

Displays loaded modules with additional details like size and reference count

snd_hda_intel 57344 1 - Live 0x0000000000000000
snd_hda_codec 139264 1 - Live 0x0000000000000000
snd_hda_core 81920 2 - Live 0x0000000000000000

modinfo <module_name>

Shows metadata and details about a specific module

filename:       /lib/modules/5.15.0-1027-oem/kernel/sound/pci/hda/snd-hda-intel.ko
alias:          pci:v00008086d00002668sv*sd*bc*sc*i*
version:        1.0.0
license:        GPL

Example: Check if a specific module is loaded

lsmod | grep snd_hda_intel

2. Loading Modules Manually

Command	Description	Notes
modprobe	Load or unload kernel modules dynamically	Automatically handles dependencies
insmod	Insert a module into the kernel	Does not handle dependencies; requires full path
rmmod	Remove a module from the kernel	Can specify module name or path

Example: Load a module with modprobe

sudo modprobe e1000

Example: Load a module with insmod

sudo insmod /lib/modules/$(uname -r)/kernel/drivers/net/e1000/e1000.ko

Example: Unload a module with rmmod

sudo rmmod e1000

Note: Use modprobe when possible as it handles dependencies and is safer than insmod.

3. Removing Modules

Command	Description	Notes
rmmod	Removes a module from the kernel	Module must be unloaded first if in use
modprobe -r	Removes a module and its dependencies	Automatically handles dependency removal

Example: Removing a Kernel Module

# Remove a specific module
sudo rmmod e1000

# Remove module and dependencies
sudo modprobe -r e1000

Note: Ensure the module is not in use before removal to avoid system instability.

Warning: Removing critical kernel modules like network drivers can cause system crashes or loss of connectivity.

4. Viewing Module Information

Command	Description	Example
lsmod	Lists currently loaded kernel modules	`lsmod`
modinfo	Displays detailed information about a specific module	`modinfo e1000`
cat /proc/modules	Shows all loaded modules with their reference counts and size	`cat /proc/modules`

Example: Check module details

modinfo snd_hda_intel

Note: The modinfo command can show version, author, description, and parameters of a module.

5. Configuring Module Parameters

Parameter	Description	Values	Default
module.param	Module-specific parameter	`value`	None

Example: Setting Module Parameter

# Load module with parameter<br>modprobe module_name.param=value

Example: Persistent Parameter Configuration

# Add to /etc/modprobe.d/module.conf<br>options module_name.param=value

6. Blacklisting Modules

Module Name	Blacklist Location	Description
snd_hda_intel	`/etc/modprobe.d/blacklist.conf`	Prevents loading of Intel HDA audio driver
nouveau	`/etc/modprobe.d/blacklist.conf`	Disables open-source NVIDIA GPU driver

Example: Blacklisting a Module

# Add to /etc/modprobe.d/blacklist.conf
blacklist snd_hda_intel

Note: Changes take effect after reboot or module reload.

7. Updating Kernel

Method	Description	Notes
apt update & apt upgrade	Update kernel packages via APT (Debian/Ubuntu-based systems)	May require reboot after update
dnf update kernel	Update kernel using DNF (Fedora/RHEL-based systems)	System will prompt to reboot if new kernel is installed
yum update kernel	Update kernel using YUM (older RHEL/CentOS systems)	Reboot required to use new kernel
pacman -Syu	Update kernel on Arch-based systems	May update all packages; reboot needed to switch kernels

Example: Update kernel on Ubuntu

$ sudo apt update
$ sudo apt upgrade

Note: Always ensure you have a backup or recovery method before updating the kernel.

Warning: Kernel updates can cause system instability or hardware incompatibility if not properly tested.

Update Process Summary

Check current kernel version: uname -r
Update package lists: apt update
Upgrade kernel packages: apt upgrade
Reboot system to use new kernel

8. Viewing Available Kernels

Command	Description	Notes
uname -r	Displays the running kernel version	Shows current kernel in use
ls /boot	List files in boot directory	Includes kernel images and initrd files
ls /lib/modules	Lists installed kernel modules	Shows available kernel versions
cat /proc/version	Displays kernel version info	Includes compiler and build details
dpkg -l \| grep linux-image	List installed Linux kernel images (Debian/Ubuntu)	Shows all installed kernels
rpm -qa \| grep kernel	List installed kernels (RHEL/CentOS/Fedora)	Lists all kernel packages

Example: Check running kernel version

$ uname -r
5.15.0-1028-oem

Example: List installed kernels (Debian/Ubuntu)

$ dpkg -l | grep linux-image
ii  linux-image-5.15.0-1028-oem  5.15.0-1028.32  amd64  Linux kernel image for version 5.15.0-1028-oem
ii  linux-image-5.15.0-1030-oem  5.15.0-1030.34  amd64  Linux kernel image for version 5.15.0-1030-oem

9. Removing Old Kernels

Command	Description	Notes
dpkg --list \| grep linux-image	List all installed Linux kernel images	Use to identify which kernels are currently installed
apt autoremove	Remove old kernel packages that are no longer needed	Automatically removes unused kernels and dependencies
apt purge linux-image-<version>	Manually remove a specific kernel version	Replace <version> with the desired kernel version to remove

Example: Remove Old Kernels

# List installed kernels
dpkg --list | grep linux-image

# Remove old kernels (keeping current and previous)
sudo apt autoremove

Note: Always ensure that at least one kernel is retained to avoid system boot issues.

Warning: Removing kernels can lead to system instability if the current kernel is removed. Always verify that the running kernel is not being removed.

10. Managing initramfs

Command	Description	Notes
update-initramfs	Creates or updates the initramfs image	Used to regenerate initramfs after kernel/module changes
mkinitramfs	Creates a new initramfs image from scratch	More manual control over the process
dracut	Tool for generating initramfs images	Alternative to update-initramfs, used in some distributions

Example: Update initramfs after kernel update

sudo update-initramfs -u

Example: Create a new initramfs image

sudo mkinitramfs -o /boot/initrd.img-$(uname -r) $(uname -r)

Note: The initramfs is a temporary filesystem loaded into memory during boot. It contains necessary drivers and tools to mount the root filesystem.