Understanding Kernel Modules

Oct 13, 2025 by vinooalluri.com 149 views

Introduction

As a Linux user, you may have encountered situations where you need to make changes to kernel module parameters persistent across reboots. This is particularly useful when you need to configure kernel modules to work around hardware issues or to optimize system performance. In this article, we will explore how to make changes to /sys/module/*/parameters persistent in Fedora and other Linux distributions.

Understanding Kernel Modules

Kernel modules are pieces of code that extend the functionality of the Linux kernel. They are loaded into memory when the system boots and can be unloaded when they are no longer needed. Kernel modules can be used to add support for new hardware, optimize system performance, or provide additional functionality.

The Problem with Persistent Changes

When you make changes to kernel module parameters, they are stored in memory and are lost when the system is rebooted. This can be frustrating, especially if you need to make changes to kernel module parameters frequently.

Solution: Using sysctl.conf

One way to make changes to kernel module parameters persistent is to use the sysctl.conf file. The sysctl.conf file is a configuration file that stores kernel module parameters and other system settings.

To make changes to kernel module parameters persistent using sysctl.conf, follow these steps:

Edit the sysctl.conf file: Open the sysctl.conf file in a text editor. The file is usually located in the /etc/sysctl.d/ directory.
Add kernel module parameters: Add the kernel module parameters you want to make persistent to the sysctl.conf file. For example, to disable USB autosuspend, you can add the following line to the file:

net.ipv4.conf.all.autonegotiate=1

Save the changes: Save the changes to the sysctl.conf file.
Reload the sysctl configuration: Reload the sysctl configuration using the following command:

sudo sysctl -p /etc/sysctl.d/*

Alternative Solution: Using kernel command line options

Another way to make changes to kernel module parameters persistent is to use kernel command line options. Kernel command line options are options that are passed to the kernel when it boots.

To make changes to kernel module parameters persistent using kernel command line options, follow these steps:

Edit the grub configuration file: Open the grub configuration file in a text editor. The file is usually located in the /etc/grub2.cfg directory.
Add kernel command line options: Add the kernel command line options you want to make persistent to the grub configuration file. For example, to disable USB autosuspend, you can add the following line to the file:

echo "usbcore.autosuspend=-1" >> /etc/grub2.cfg

Save the changes: Save the changes to the grub configuration file.
Update the grub configuration: Update the grub configuration using the following command:

sudo update-grub

Alternative Solution: Using kernel module parameters files

Kernel module parameters files are files that store kernel module parameters. These files are usually located in the /etc/modprobe.d/ directory.

To make changes to kernel module parameters persistent using kernel module parameters files, follow these steps:

Create a kernel module parameters file: Create a new file in the /etc/modprobe.d/ directory. For example, you can create a file called usb-autosuspend.conf.
Add kernel module parameters: Add the kernel module parameters you want to make persistent to the file. For example, to disable USB autosuspend, you can add the following line to the file:

options usbcore autosuspend=-1

Save the changes: Save the changes to the file.
Reload the kernel module parameters: Reload the kernel module parameters using the following command:

sudo modprobe -r usbcore
sudo modprobe usbcore

Conclusion

Making changes to kernel module parameters persistent can be a challenge, but there are several solutions available. In this article, we explored three solutions: using sysctl.conf, kernel command line options, and kernel module parameters files. By following the steps outlined in this article, you can make changes to kernel module parameters persistent and avoid the frustration of having to make changes repeatedly.

Additional Tips and Tricks

Use the sysctl command: The sysctl command is a powerful tool that allows you to view and modify kernel module parameters. You can use the sysctl command to view the current value of a kernel module parameter and to modify its value.
Use the modprobe command: The modprobe command is a tool that allows you to load and unload kernel modules. You can use the modprobe command to load a kernel module and to unload it.
Use the grub command: The grub command is a tool that allows you to configure the grub bootloader. You can use the grub command to add kernel command line options and to update the grub configuration.

References

Fedora Documentation: sysctl.conf
Fedora Documentation: kernel command line options
Fedora Documentation: kernel module parameters files
Q&A: Making Changes to /sys/module/*/parameters Persistent ===========================================================

**Q: What is the purpose of the /sys/module/*/parameters directory?**

A: The /sys/module/*/parameters directory is a directory that stores kernel module parameters. Kernel module parameters are settings that can be modified to configure the behavior of kernel modules.

Q: Why do kernel module parameters need to be made persistent?

A: Kernel module parameters need to be made persistent because they are lost when the system is rebooted. This can be frustrating, especially if you need to make changes to kernel module parameters frequently.

Q: How can I make changes to kernel module parameters persistent?

A: There are several ways to make changes to kernel module parameters persistent. Some of the most common methods include:

Using the sysctl.conf file
Using kernel command line options
Using kernel module parameters files

Q: What is the sysctl.conf file and how do I use it?

A: The sysctl.conf file is a configuration file that stores kernel module parameters and other system settings. To use the sysctl.conf file, you need to edit it to add the kernel module parameters you want to make persistent. Then, you need to reload the sysctl configuration using the sysctl -p command.

Q: What are kernel command line options and how do I use them?

A: Kernel command line options are options that are passed to the kernel when it boots. To use kernel command line options, you need to edit the grub configuration file to add the options you want to make persistent. Then, you need to update the grub configuration using the update-grub command.

Q: What are kernel module parameters files and how do I use them?

A: Kernel module parameters files are files that store kernel module parameters. To use kernel module parameters files, you need to create a new file in the /etc/modprobe.d/ directory and add the kernel module parameters you want to make persistent. Then, you need to reload the kernel module parameters using the modprobe command.

Q: How do I reload the kernel module parameters after making changes to the sysctl.conf file?

A: To reload the kernel module parameters after making changes to the sysctl.conf file, you need to use the sysctl -p command. This command reloads the sysctl configuration and applies the changes you made to the sysctl.conf file.

Q: How do I reload the kernel module parameters after making changes to the kernel command line options?

A: To reload the kernel module parameters after making changes to the kernel command line options, you need to update the grub configuration using the update-grub command. This command updates the grub configuration and applies the changes you made to the kernel command line options.

Q: How do I reload the kernel module parameters after making changes to the kernel module parameters files?

A: To reload the kernel module parameters after making changes to the kernel module parameters files, you need to use the modprobe command. This command reloads the kernel module parameters and applies the changes you made to the kernel module parameters files.

Q: What are some common kernel module parameters that need to be made persistent?

A: Some common kernel module parameters that need to be made persistent include:

usbcore.autosuspend: This parameter controls whether USB devices are put into autosuspend mode.
net.ipv4.conf.all.autonegotiate: This parameter controls whether the network interface is put into autonegotiate mode.
vm.swappiness: This parameter controls the swappiness of the system.

Q: How do I troubleshoot issues with making changes to kernel module parameters persistent?

A: To troubleshoot issues with making changes to kernel module parameters persistent, you can use the following steps:

Check the sysctl.conf file to ensure that the kernel module parameters are correctly configured.
Check the grub configuration file to ensure that the kernel command line options are correctly configured.
Check the kernel module parameters files to ensure that the kernel module parameters are correctly configured.
Use the sysctl command to view the current value of the kernel module parameters.
Use the modprobe command to reload the kernel module parameters.
Use the update-grub command to update the grub configuration.