Linux what are kernel headers

Linux kernel headers

I’ve been looking into this matter a little bit myself recently.

I don’t know how related this answer is since it sounds like you are only concerned about understanding the packaging of the kernel source you have on hand. This answer probably only pertains to your second question. Nevertheless here is some stuff I’ve found about kernel headers.

From what I’ve found there are two potential locations that end up being referred to as «kernel headers».

The first location is in /usr/src/linux-headers-`version’ (at least on my Ubuntu machine). This is where your kernel (source?) is installed as well as the accompanying headers. If you want to build kernel modules then you will need to build against the headers found here.

On the other hand /usr/include/ also contain «kernel headers». You can think of these header files as the userland interface to your kernel. It is the API exported by the kernel so userland programs can make system calls. Your libc will take advantage of this API so it can create functions (in /usr/include) based on which system calls are available.

Here are a couple of documents to back up what I’ve just said and to clarify things a bit more:

Here is a link about the difference between /usr/src/linux-headers-`version’ and /usr/include on RHEL4.

Finally here is another explanation of what kernel headers are for: http://www.overclockers.com/forums/showthread.php?t=647638

So maybe you knew this already and you just wanted to know how to create a driver using the sources in your kernel package, but at least with this answer you know that its definitely the place to start.

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How to install kernel headers on Debian

All instructions in this tutorial are also useful for other Debian-based Linux distributions such as Ubuntu.

Installing kernel headers on Debian 11:

First, update the information on your software using apt, as shown in the example below.

Check for available Linux kernel headers by running the following command.

For a different simple way to list available headers, run the command below.

To install the Linux kernel headers, run the command shown in the screenshot below.

Using Debian 11 x64 or using the second method to find the header, you can also run the following command.

In my case, the headers were installed in the previous example, so the output says it’s already properly installed.

What is the Linux kernel?

Some experts say the kernel is the core component of an Operating System; others disagree and say the kernel is not part of the OS but a vital component needed by any OS. The function of the kernel is to manage the device resources for them to interact with the operating system and applications. We can think about the kernel as a translator allowing communication between the hardware and the software. In order to manage resources properly, the kernel has full privileges. In some cases, the installed kernel may lack the proper code to allow the hardware and software interaction; that’s when we need to install kernel headers.

What are Linux Kernel Headers?

Linux kernel headers are components usually used to compile drivers and loadable modules adding support to the kernel. For this purpose, kernel headers include C headers with functions and structures needed to compile modules. Thanks to kernel headers, modules or drivers can interact with the kernel. It is important to clarify the kernel headers are part of the kernel, despite being distributed separately.

Dealing with kernel headers is easier than dealing with whole kernel sources. If you are looking for drivers for a device, you’ll use kernel headers, while to rebuild the whole kernel, you will need whole kernel sources. By default, some Linux distributions, including Debian, include the kernel headers to be used if needed (this tutorial assumes you discarded or removed the headers). If all your hardware works properly, you probably won’t need to deal with kernel headers.

Conclusion:

As you can see, installing Linux kernel headers on Debian or Ubuntu is pretty easy. Any Linux-level user should know the function of kernel headers and how to install them. Users must pay attention to the kernel headers they download that are compatible with their system, not only the architecture but also the version.

Thank you for reading this tutorial explaining how to install kernel headers on Debian. Keep following Linux Hint for additional Linux tips and tutorials.

About the author

David Adams

David Adams is a System Admin and writer that is focused on open source technologies, security software, and computer systems.

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How to Install Linux Kernel Headers on Fedora 38/37/36 Linux

If you use a Fedora Linux system, you may need to install missing kernel headers to build and install specific software. This guide will show you how to install missing kernel headers on Fedora.

What are Linux Kernel Headers? Explained

Linux Kernel Headers are crucial for connecting the Linux Kernel with user-space programs. They consist of a collection of C header files that define all the interfaces and data structures used by the kernel. These headers enable direct communication between user-space programs and the kernel, allowing user-space software to access information about the kernel’s configuration, such as its version or build options. This makes it easier for users to build Linux-specific software on their machines. Understanding the importance of Linux Kernel Headers is essential for new users who want to delve deeper into their system’s configuration.

Step 1: Update Fedora

Before proceeding, ensure your system is up-to-date regarding the Linux Kernel. If any Linux Kernel packages are updated, ensure to restart your system.

Step 2: Check the Current Linux Kernel

First, to install the missing kernel headers, it’s essential to check the current kernel version. This step can be done by executing the following command in the terminal.

The command will show the version of the currently running kernel. Note this version as it will be needed in the next step.

Step 3: Install Linux Kernel Headers

After identifying the kernel version, the kernel headers package can be installed. On Fedora Linux, this can be done by executing the following command in the terminal.

sudo dnf install kernel-headers

Sometimes this may work but not correctly if you install Nvidia Drivers; you may need to use the following command instead.

sudo dnf install kernel-headers-$(uname -r) 

This command installs the kernel headers package corresponding to the currently running kernel version. Now, rebooting your Fedora system after installing any kernel packages is an optional step that you may choose to take.

Step 4: Verify Linux Kernel Headers Installation

After installing the headers package for your Linux Kernel, you can verify the successful installation by running the following command.

sudo dnf list installed | grep kernel-headers

This command will show a list of all the installed kernel-headers packages. The package you recently installed should be visible in the list.

kernel-headers.x86_64 6.1.5-200.fc37 @updates 

Conclusion:

In conclusion, installing Linux Kernel headers on Fedora is a straightforward process that involves checking the current kernel version, installing the matching headers package, and verifying the installation. These steps ensure the kernel headers are in place for building and installing specific software.

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How to Install Linux Kernel Headers on Rocky Linux

If you’re working on a Rocky Linux system, you may need to install missing Linux kernel headers to build and install specific software. This guide demonstrates installing the missing kernel headers on Rocky Linux 9 and Rocky Linux 8 distributions.

What are Linux Kernel Headers? Explained

Linux Kernel Headers provide a vital connection between the Linux Kernel and user-space programs. Essentially, these headers are a collection of C header files that define all of the interfaces and data structures used by the kernel. Irrespective of the purpose, these definitions make possible direct communication between user-space programs and Kernel. With the help of these headers, user-space software can obtain information about the configuration of their Linux Kernel – such as the version or build options. As a result, building Linux-specific software on user machines becomes relatively easy due to this collection of headers, as it allows users to interact with their kernel effectively. Knowing that Linux Kernel Headers are key components of any Linux system is paramount for newer users who want to dig deeper into the configuration wirings on their system.

Step 1: Update Rocky Linux

First, ensure your system is up-to-date, especially in regards to the Linux Kernel; ensure you do a restart if any Linux Kernel packages are updated before proceeding.

Step 2: Check the Current Linux Kernel

Before installing the missing kernel headers, it’s important to check the current kernel version. This can be done by running the following command in the terminal.

This command will display the version of the currently running kernel. Note this version, as it will be used in the next step.

Example output from my machine:

Step 3: Install Linux Kernel Headers

Once the kernel version has been determined, the kernel headers package can be installed. On Rocky Linux, this can be done by running the following command in the terminal.

sudo dnf install kernel-headers-$(uname -r)

This command will install the kernel headers package corresponding to the currently running kernel version. The package manager and package name may differ if you use a different version of Linux.

Optionally, once installing any kernel packages, you may want to reboot your system.

Step 4: Verify Linux Kernel Headers Installation

Now that you have installed the headers package for your Linux Kernel run the following command to verify that the kernel headers have been successfully installed.

sudo dnf list installed | grep kernel-headers

This command will display a list of all installed kernel headers packages, and the package you just installed should be listed there.

kernel-headers.x86_64 5.14.0-162.6.1.el9_1.0.1 @appstream 

Conclusion:

Installing missing Linux Kernel headers on Rocky Linux is a simple process that can be accomplished by checking the currently installed kernel version, installing the corresponding kernel headers package, and verifying the installation. These steps should ensure that the necessary kernel headers are in place for building and installing specific software.

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What exactly are Linux kernel headers? [duplicate]

I know that if I want to compile my own Linux kernel I need the Linux kernel headers, but what exactly are they good for? I found out that under /usr/src/ there seem to be dozens of C header files. But what is their purpose, aren’t they included in the kernel sources directly?

3 Answers 3

The header files define an interface: they specify how the functions in the source file are defined.

They are used so that a compiler can check if the usage of a function is correct as the function signature (return value and parameters) is present in the header file. For this task the actual implementation of the function is not necessary.

You could do the same with the complete kernel sources but you will install a lot of unnecessary files.

Example: if I want to use the function

in a program I do not need to know how the implementation of foo is, I just need to know that it accepts a single param ( double ) and returns an integer.

As stated, header files define interfaces to functions as well as structures used by programs.

In the case of the kernel header files, these functions and structures are within the kernel itself.

If you are building a complete kernel, then, obviously, you need the complete source files, not just the headers. However, if you are compiling a device driver or other loadable module which links into the kernel then you only need the header files, so can save space by not installing the full sources.

The separation of packages so that you can install just the header files is partly historical as the difference in disk usage used to be a significant consideration when disks were smaller. These days, having the entire source on disk (unnecessarily) would not be a major disk space consideration.

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