About Kernel Modules

The boot loader loads the kernel into memory. You can add new code to the kernel by including the source files in the kernel source tree and recompiling the kernel. Kernel modules provide device drivers that enable the kernel to access new hardware, support different file system types, and extend its functionality in other ways. The modules can be dynamically loaded and unloaded on demand. To avoid wasting memory on unused device drivers, Oracle Linux supports loadable kernel modules (LKMs), which enable a system to run with only the device drivers and kernel code that are required to be loaded into memory. See Managing Kernel Modules to see more information on how to manage kernel modules on Oracle Linux.

Note:

From UEK R7 onward, kernel packaging changes are applied to provide a more streamlined kernel. Kernel modules that are required for most server configurations are provided in the kernel-uek-modules package, while optional kernel modules for hardware less often found in server configurations, such as Bluetooth, Wi-Fi, and video capture cards, can be found in the kernel-uek-modules-extra package. Note that both of these packages require the linux-firmware package to be installed.

You can view the contents of these packages by running:

dnf repoquery -l kernel-uek-modules
dnf repoquery -l kernel-uek-modules-extra

To install all available kernel modules, run:

sudo dnf install -y kernel-uek-modules kernel-uek-modules-extra linux-firmware

See Unbreakable Enterprise Kernel Release 7: Release Notes (5.15.0-0.30).

Kernel modules can be signed to protect the system from running malicious code at boot time. When UEFI Secure Boot is enabled, only kernel modules that contain the correct signature information can be loaded. See Oracle Linux: Working With UEFI Secure Boot for more information.

About Weak Update Modules

External modules, such as drivers that are installed by using a driver update disk or that are installed from an independent package, are typically installed in the /lib/modules/kernel-version/extra directory. Modules that are stored in this directory are preferred over any matching modules that are included with the kernel when these modules are being loaded. Installed external drivers and modules can override existing kernel modules to resolve hardware issues. For each kernel update, these external modules must be made available to each compatible kernel so that potential boot issues resulting from driver incompatibilities with the affected hardware can be avoided.

Because the requirement to load the external module with each compatible kernel update is system critical, a mechanism exists for external modules to be loaded as weak update modules for compatible kernels.

You make weak update modules available by creating symbolic links to compatible modules in the /lib/modules/kernel-version/weak-updates directory. The package manager handles this process automatically when it detects driver modules that are installed in the /lib/modules/kernel-version/extra directories for any compatible kernels.

For example, if a newer kernel is compatible with a module that was installed for the previous kernel, an external module (such as kmod-kvdo) is automatically added as a symbolic link in the weak-updates directory as part of the installation process, as shown in the following command output:

ls -l /lib/modules/5.15.0-208.159.3.2.el8.x86_64/weak-updates/kmod-kvdo/uds

lrwxrwxrwx. 1 root root 68 Jul  8 07:57 uds.ko -> 
/lib/modules/5.15.0-208.159.3.2.el8.x86_64/extra/kmod-kvdo/uds/uds.ko

ls -l /lib/modules/5.15.0-208.159.3.2.el8.x86_64/weak-updates/kmod-kvdo/vdo

lrwxrwxrwx. 1 root root 68 Jul  8 07:57 uds.ko -> 
/lib/modules/5.15.0-208.159.3.2.el8.x86_64/extra/kmod-kvdo/uds/uds.ko

The symbolic link enables the external module to load for kernel updates.

Weak updates are beneficial and ensure that no extra work is required to carry an external module through kernel updates. Any potential driver-related boot issues after kernel upgrades are prevented, so this approach provides a more predictable running of a system and its hardware.

You can remove weak update modules if a kernel version provides a superior or preferred driver or module version. See Removing Weak Update Modules for more information.

For more information about external driver modules and driver update disks, see Oracle Linux 8: Installing Oracle Linux.