What are linux kernel header files

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.

Check Kernel Version and Kernel Headers in Ubuntu

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.

Check Kernel Headers in Ubuntu

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.

Install Kernel Headers in Ubuntu

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

Verify Installed Kernel Headers in Ubuntu

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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Linux kernel headers

I want to understand, what type of header files are placed under «/includes/» in the base directory of the kernel. Are these files intended to be the «public» headers/API’s in some sense ? Thereby being, oblivious of the architecture, config switches that have been enabled/disabled etc ?

In short, if I want to use some core kernel functionality within my driver, may I safely assume that the functionality I am looking for, would be contained in one of the relevant header files under «/includes» and nowhere else ?

Look forward to some comments.

2 Answers 2

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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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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Exporting kernel headers for use by userspace¶

The “make headers_install” command exports the kernel’s header files in a form suitable for use by userspace programs.

The linux kernel’s exported header files describe the API for user space programs attempting to use kernel services. These kernel header files are used by the system’s C library (such as glibc or uClibc) to define available system calls, as well as constants and structures to be used with these system calls. The C library’s header files include the kernel header files from the “linux” subdirectory. The system’s libc headers are usually installed at the default location /usr/include and the kernel headers in subdirectories under that (most notably /usr/include/linux and /usr/include/asm).

Kernel headers are backwards compatible, but not forwards compatible. This means that a program built against a C library using older kernel headers should run on a newer kernel (although it may not have access to new features), but a program built against newer kernel headers may not work on an older kernel.

The “make headers_install” command can be run in the top level directory of the kernel source code (or using a standard out-of-tree build). It takes two optional arguments:

ARCH indicates which architecture to produce headers for, and defaults to the current architecture. The linux/asm directory of the exported kernel headers is platform-specific, to see a complete list of supported architectures use the command:

INSTALL_HDR_PATH indicates where to install the headers. It defaults to “./usr”.

An ‘include’ directory is automatically created inside INSTALL_HDR_PATH and headers are installed in ‘INSTALL_HDR_PATH/include’.

© Copyright The kernel development community.

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Как установить заголовочные файлы ядра в Linux

Когда вы компилируете драйвер устройства как модуль ядра, вам необходимы установленные заголовочные файлы ядра. Также они требуются, если вы собираете пользовательское приложение, которое взаимодействует напрямую с ядром. При установке заголовочных файлов ядра, необходимо убедиться, что их версия совпадает с версией ядра установленного в системе.

Если версия вашего ядра не менялась после установки дистрибутива, или вы обновляли его с использованием системного менеджера пакетов (то есть apt-get, aptitude или yum) из системных репозиториев, то заголовочные файлы вы также можете установить с помощью пакетного менеджера. Однако если вы скачивали исходный код ядра и компилировали его самостоятельно, то заголовочные файлы необходимо устанавливать с помощью команды make.

Здесь мы предполагаем, что ваше ядро установлено из основного системного репозитория вашего дистрибутива, и вы хотите установить соответствующие заголовочные файлы ядра.

Установка заголовочных файлов ядра в Debian, Ubuntu или Linux Mint

Если вы не компилировали ядро вручную, то можете установить соответствующие заголовочные файлы ядра с помощью команды apt-get.
Сначала проверьте, не установлены ли уже требуемые заголовочные файлы с помощью команды:

Теперь установите заголовочные файлы, как показано ниже.

Проверьте, что установка прошла успешно.

По умолчанию в Debian, Ubuntu или Linux Mint заголовочные файлы находятся в /usr/src.

Установка заголовочных файлов ядра в Fedora, CentOS или RHEL

Если вы не обновляли ядро вручную, то можете установить соответствующие заголовочные файлы ядра с помощью команды yum.
Сначала проверьте, не установлены ли уже требуемые заголовочные файлы. По умолчанию заголовочные файлы ядра расположены в /usr/src/kernels/.
Если подходящих заголовочных файлов не установлено, вы можете установить их с помощью команды yum. Она автоматически найдет подходящий пакет.

Если заголовочные файлы ядра, установленные с помощью вышеприведенной команды, не соответствуют установленному в системе ядре, значит оно устарело. В этом случае обновите ядро системы до последней версии с помощью приведенной ниже команды. После обновления необходимо перезагрузить систему.

Теперь проверьте, что установлены заголовочные файлы соответствующей версии с помощью команды:

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