How do you use kernel module and driver parameters to customize functionality and behavior?

1 What are kernel module and driver parameters?

Kernel module and driver parameters are special options that you can pass to the kernel or the drivers when they are loaded or inserted into the system. They allow you to modify the default settings or features of the modules or drivers, and thus affect how they interact with the hardware or the software. For example, you can use parameters to enable or disable certain functions, change the values of variables, or select different modes of operation.

2 How to find available parameters?

Before using parameters, you should be aware of the parameters available for a given module or driver, and what they do. There are several ways to gather this information, depending on the source and type of the module or driver. For instance, you can read the documentation or source code of the module or driver if available. Alternatively, you can use the modinfo command to display information about a module, including its parameters and their descriptions. Additionally, you can access the parameters of a loaded module or driver through the sysfs interface under the /sys/module or /sys/bus directories. Lastly, you can use the dmesg command to view kernel messages that may show the parameters and their values.

3 How to pass parameters to the kernel?

One way to pass parameters to the kernel is to edit the bootloader configuration file, such as /etc/default/grub for GRUB, and add the parameters to the end of the line that starts with GRUB_CMDLINE_LINUX. For example, if you want to pass the parameter acpi_osi=Linux to the kernel, you would add it like this:

GRUB_CMDLINE_LINUX="... acpi_osi=Linux"

Then, you need to update the bootloader with the update-grub command and reboot the system for the changes to take effect.

Another way to pass parameters to the kernel is to use the kexec command, which allows you to load a new kernel without rebooting the system. However, this method requires that you have the kexec-tools package installed and that you have a compatible kernel image and initramfs file ready. For example, if you want to pass the parameter debug to the kernel, you would run something like this:

kexec -l /boot/vmlinuz --initrd=/boot/initrd.img --append="... debug"

kexec -e

4 How to pass parameters to the modules?

One way to pass parameters to the modules is to use the modprobe command, which loads or removes modules and their dependencies. You can specify the parameters after the module name, separated by spaces. For example, if you want to load the e1000e module with the parameter SmartPowerDownEnable=1, you would run something like this:

modprobe e1000e SmartPowerDownEnable=1

Another way to pass parameters to the modules is to create a configuration file under the /etc/modprobe.d directory, with a .conf extension, and write the parameters in the format of module_name parameter=value. For example, if you want to load the snd_hda_intel module with the parameter model=generic, you would create a file named snd_hda_intel.conf and write this:

snd_hda_intel model=generic

Then, you need to reload the module with the modprobe -r and modprobe commands for the changes to take effect.

5 How to pass parameters to the drivers?

One way to pass parameters to the drivers is to use the udev rules, which are files that define actions to be performed when a device is detected or removed. You can create a udev rule file under the /etc/udev/rules.d directory, with a .rules extension, and write the parameters in the format of ATTR{parameter}=value. For example, if you want to set the brightness of your backlight device to 50%, you would create a file named backlight.rules and write this:

SUBSYSTEM=="backlight", ATTR{brightness}="50"

Then, you need to reload the udev rules with the udevadm control --reload-rules command for the changes to take effect.

Another way to pass parameters to the drivers is to use the sysfs interface, which is a virtual filesystem that exposes the attributes of devices and drivers. You can access the sysfs files under the /sys directory, and write the parameters to them with the echo command. For example, if you want to set the speed of your fan device to 3000 RPM, you would run something like this:

echo 3000 > /sys/class/hwmon/hwmon0/fan1_target

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?