Linux kernel and headers

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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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 Kernel Headers in Ubuntu and Debian

In our last article, we have explained how to install kernel headers in CentOS 7. Kernel Headers contain the C header files for the Linux kernel, which offers the various function and structure definitions required when compiling any code that interfaces with the kernel, such as kernel modules or device drivers and some user programs.

It is very important to note that the kernel headers package you install should match with the currently installed kernel version on your system. If your kernel version ships with the default distribution installation or you have upgraded your Kernel using dpkg or apt package manager from the Ubuntu or Debian base repositories, then you must install matching kernel headers using package manager only. And if you’ve compiled kernel from sources, you must also install kernel headers from sources.

In this article, we will explain how to install Kernel Headers in Ubuntu and Debian Linux distributions using default package manager.

Install Kernel Headers in Ubuntu and Debian

First check your installed kernel version as well as kernel header package that matches your kernel version using following commands.

$ uname -r $ apt search linux-headers-$(uname -r)

On Debian, Ubuntu and their derivatives, all kernel header files can be found under /usr/src directory. You can check if the matching kernel headers for your kernel version are already installed on your system using the following command.

$ ls -l /usr/src/linux-headers-$(uname -r)

From the above output, it’s clear that the matching kernel header directory doesn’t exist, meaning the package is not yet installed.

Before you can install the appropriate kernel headers, update your packages index, in order to grab information about the latest package releases, using the following command.

Then run the following command that follows to install the Linux Kernel headers package for your kernel version.

$ sudo apt install linux-headers-$(uname -r)

Next, check if the matching kernel headers have been installed on your system using the following command

$ ls -l /usr/src/linux-headers-$(uname -r)

That’s all! In this article, we have explained how to install kernel headers in Ubuntu and Debian Linux and other distributions in the Debian family tree.

Always keep in mind that to compile a kernel module, you will need the Linux kernel headers. If you have any quires, or thoughts to share, use the comment form below to reach us.

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How do I install kernel header files?

You should be able to install the kernel header files for the currently running kernel by running the following in a terminal:

sudo apt-get install linux-headers-$(uname -r) 

In general, the kernel header packages are named linux-header-* where «*» indicates the version & variant (generic, server, etc.).

hey thanks but could you tell me what does generic, server, etc means i want to write (kernel driver)

This won’t install the headers for future updates automatically and you’ll have to re-run this command every time. Therefore, it’s recommended to install the metapackage instead, as described in another answer.

sudo apt-get install linux-headers-generic 

if you are on a Desktop installation. The apt-get will solve the dependencies and install the correct version of kernel headers.

In Debian Wheezy I get the error message «Package linux-headers-generic is not available, but is referred to by another package. [. ] E: Package ‘linux-headers-generic’ has no installation candidate»

@IQAndreas the linux-headers-generic package is ubuntu specific. On Debian you should use sudo apt-get install linux-headers-$(uname -r)

I have linux-headers-generic installed on 18.04 but still don’t have the headers for the newest and current kernel version. Maybe it’s just a bug with this version, I’ve compiled kernel modules in earlier versions so I must’ve had the correct headers back then.

Case of Obsolete kernel package

This should cover another problem when: the currently running kernel is obsolete, meaning it’s not in the repository anymore neither its headers. So the best thing to do is to update the kernel to last version in the repository.

linux-generic is a meta package to keep current version of the kernel & its headers:

sudo apt-get update sudo apt-get install linux-generic 

Note: Depending on your Ubuntu edition, See if you need linux-lowlatency (Ubuntu Studio), linux-signed-generic or linux-virtual .

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What are Linux Headers – How to Install Linux Kernel Headers on Kali?

A computer or software program contains multiple source files. Many source files need common declarations and functions to operate. Instead of reproducing the same code in each source file, separate files are introduced as an interface between the source files. These files are known as header files. The concept of Linux headers is similar to these header files. The Linux-headers is a package that provides an interface between Kernel internal components, and between Kernel and external memory resources. The kernel is the core program in any Operating System (OS). When an OS boots; Kernel loads after boot loader. It controls various activities including task management, memory management, disk management, etc. For instance, when multiple processes run on an operating system, the Kernel provides uniform resource access to all the running processes. Similarly, the Kernel is responsible for allocating and de-allocating the memory resources to the applications. Since Kernel itself is a program (mostly developed in C language), it also requires memory space to execute the code. The space reserved for Kernel code execution is called the Protected Kernel Space. The protected Kernel space is inaccessible by other applications. The space used by other applications is known as userspace. Therefore, an interface is required between the protected space and the userspace. This interface is provided by the Linux headers.

How to Automatically Install Linux Headers?

Before installing Linux headers, it is important to upgrade the available packages and remove the obsolete ones. First, we need to update the packages list to get information about the latest available versions of the installed packages and dependencies. This can be achieved with the following command.

After updating the packages list, we can download and install the available updates using the dist-upgrade command.

Note: The sudo apt-get upgrade command only upgrades the newest available versions of the installed packages, whereas the sudo apt-get dist-upgrade also removes the obsolete packages from the system.

When the upgrading process completes, reboot the system for the changes to take effect.

After rebooting the system, we can install the Linux-headers package using any of the following commands.

1# sudo apt-get install –y linux-headers-$(uname -r) 2# sudo apt-get install –y linux-headers

In the first command, the uname -r parameter fetches the installed Kernel version on the system.

We can manually verify the Kernel version using the following command.

sudo apt-get install –y linux-headers-$(uname -r)

We can also search for specific Linux headers using the following command.

sudo apt search linux-headers

After finding the appropriate package, we can install it as follows.

sudo apt-get install –y linux-headers-

For instance, we can install the 5.10.0-kali9-amd64 package using the following syntax.

sudo apt-get install –y linux-headers-5.10.0-kali9-amd64

How to Manually Install Linux Headers?

Besides the automated installation, we can manually install the Linux headers from the following repository.

https://http.kali.org/kali/pool/main/l/linux/

Scroll down the list to find the desired Linux-headers package. Let’s assume we are interested in installing the Linux-headers-5.10.0-kali4-amd64_5.10.19-1kali1_amd64.deb package from the list.

We can install this package with the help of the following command.

sudo dpkg -i linux-headers-5.10.0-kali4-amd64_5.10.19-1kali1_amd64.deb

The Linux headers play the role of a bridge for many Kernel operations. The Kernel requires the services of Linux headers for protected as well as open memory processes. The upgrading of the existing Kernel version is important for the smooth installation of Linux headers.

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