Debian 的核心儘量納入所有的功能，以及最多的驅動程式，以便涵蓋現在的硬體組態。所以，有些使用者寧願自行編譯祗包括所需的核心。這麼做有兩個理由。第一，記憶體用量較小，核心程式碼，即使未用到，也佔有記憶體的空間 (而且永遠不 “離開” 置換記憶體，因為它用到實際的 RAM)，降低系統的整體效能。在地自行編譯的核心也限制了安全問題的範圍，因為祗編譯與執行部份核心碼。
使用祗在補丁內的功能 (不在標準的核心內) 時，就必須重新編譯核心。
Debian 以套件方式管理核心，與傳統的編譯安裝不同調。核心還是在套件系統的控制下，可以被完整移除，或布建在多個機器上。與該等套件有關的腳本自動與啟動程式和 initrd 產生器互動。
The upstream Linux sources contain everything needed to build a Debian package of the kernel. But you still need to install build-essential to ensure that you have the tools required to build a Debian package. Furthermore, the configuration step for the kernel requires the libncurses-dev package (formerly libncurses5-dev, which is now a transitional package). Finally, the fakeroot package will enable creation of the Debian package without using administrator's rights.
Like anything that can be useful on a Debian system, the Linux kernel sources are available in a package. To retrieve them, just install the
linux-source-version package. The
apt search ^linux-source command lists the various kernel versions packaged by Debian. The latest version is available in the
Unstable distribution: you can retrieve them without much risk (especially if your APT is configured according to the instructions of
節 6.2.6, “在多個發行版工作”). Note that the source code contained in these packages does not correspond precisely with that published by Linus Torvalds and the kernel developers; like all distributions, Debian applies a number of patches, which might (or might not) find their way into the upstream version of Linux. These modifications include backports of fixes/features/drivers from newer kernel versions, new features not yet (entirely) merged in the upstream Linux tree, and sometimes even Debian specific changes.
The remainder of this section focuses on the 5.10 version of the Linux kernel, but the examples can, of course, be adapted to the particular version of the kernel that you want.
We assume the linux-source-5.10 package has been installed. It contains /usr/src/linux-source-5.10.tar.xz, a compressed archive of the kernel sources. You must extract these files in a new directory (not directly under /usr/src/, since there is no need for special permissions to compile a Linux kernel): ~/kernel/ is appropriate.
$ mkdir ~/kernel; cd ~/kernel
$ tar -xaf /usr/src/linux-source-5.10.tar.xz
To build a kernel from the pristine sources, just download the tarball of the version of your choice from
kernel.org, verify the integrity after importing the kernel maintainers key, and then proceed as described in the following chapters.
下個步驟是根據需要組態核心。確切的程序視需要而訂。
When recompiling a more recent version of the kernel (possibly with an additional patch), the configuration will most likely be kept as close as possible to that proposed by Debian. In this case, and rather than reconfiguring everything from scratch, it is sufficient to copy the
/boot/config-version file (the version is that of the kernel currently used, which can be found with the
uname -r command) into a
.config file in the directory containing the kernel sources. Make sure to read sidebar
TIP Missing debian/certs/debian-uefi-certs.pem in this case.
$ cp /boot/config-5.10.0-8-amd64 ~/kernel/linux-source-5.10/.config
需要改變組態的話，就跳至
節 8.10.4, “編譯與建立套件”。或者從基本開始重新組態，就需花時間組態核心。在核心原始碼的資料夾內有很多專屬介面，供呼叫
make target 命令，讓
target 是下列的其中一個值。
make menuconfig compiles and executes a text-mode interface (this is where the libncurses-dev package is required) which allows navigating the options available in a hierarchical structure. Pressing the Space key changes the value of the selected option, and Enter validates the button selected at the bottom of the screen; Select returns to the selected sub-menu; Exit closes the current screen and moves back up in the hierarchy; Help will display more detailed information on the role of the selected option. The arrow keys allow moving within the list of options and buttons. To exit the configuration program, choose Exit from the main menu. The program then offers to save the changes you've made; accept if you are satisfied with your choices.
Other interfaces have similar features, but they work within more modern graphical interfaces; such as make xconfig which uses a Qt graphical interface, and make gconfig which uses GTK+. The former requires qtbase5-dev, while the latter depends on libglade2-dev and libgtk2.0-dev.
使用這些組態介面時，建議從合理的預設組態開始。提供該等組態的核心在 arch/arch/configs/*_defconfig，然後可將選定的組態置於像 make x86_64_defconfig (64 位元電腦) 或 make i386_defconfig (32 位元電腦) 這樣的命令。
Once the kernel configuration is ready, a simple make deb-pkg will generate up to 5 Debian packages:
- linux-image-version
contains the kernel image and the associated modules,
- linux-headers-version
contains the header files required to build external modules,
- linux-firmware-image-version
contains the firmware files needed by some drivers (this package might be missing when you build from the kernel sources provided by Debian),
- linux-image-version-dbg
contains the debugging symbols for the kernel image and its modules (only created if CONFIG_DEBUG_INFO=y), and
- linux-libc-dev
contains headers relevant to some user-space libraries like GNU glibc.
The version is defined by the concatenation of the upstream version (as defined by the variables VERSION, PATCHLEVEL, SUBLEVEL, and EXTRAVERSION in the Makefile), of the LOCALVERSION configuration parameter, and of the LOCALVERSION environment variable. The package version reuses the same version string with an appended revision that is regularly incremented (and stored in .version), except if you override it with the KDEB_PKGVERSION environment variable.
$ make deb-pkg LOCALVERSION=-falcot KDEB_PKGVERSION=$(make kernelversion)-1
[...]
$ ls ../*.deb
../linux-headers-5.10.46-falcot_5.10.46-1_amd64.deb
../linux-image-5.10.46-falcot_5.10.46-1_amd64.deb
../linux-image-5.10.46-falcot-dbg_5.10.46-1_amd64.deb
../linux-libc-dev_5.10.46-1_amd64.deb
The whole process requires around 20 GB of free space, at least 8 GB of RAM, and several hours of compilation (utilizing one core) for a standard amd64 Debian kernel. These requirements can be drastically reduced by disabling the debug information using CONFIG_DEBUG_INFO=n, but this will make it impossible to trace kernel errors (“oops”) using gdb and also stop the creation of the linux-image-version-dbg package.
Some modules are maintained outside of the official Linux kernel. To use them, they must be compiled alongside the matching kernel. A number of common third party modules are provided by Debian in dedicated packages, such as vpb-driver-source (extra modules for Voicetronix telephony hardware) or leds-alix-source (driver of PCEngines ALIX 2/3 boards).
These packages are many and varied, apt-cache rdepends module-assistant$ can show the list provided by Debian. However, a complete list isn't particularly useful since there is no particular reason for compiling external modules except when you know you need it. In such cases, the device's documentation will typically detail the specific module(s) it needs to function under Linux.
For example, let's look at the dahdi-source package: after installation, a .tar.bz2 of the module's sources is stored in /usr/src/. While we could manually extract the tarball and build the module, in practice we prefer to automate all this using the DKMS framework (Dynamic Kernel Module Support). Most modules offer the required DKMS integration in a package ending with a -dkms suffix. In our case, installing dahdi-dkms is all that is needed to compile the kernel module for the current kernel provided that we have the linux-headers-* package matching the installed kernel. For instance, if you use linux-image-amd64, you would also install linux-headers-amd64.
$ sudo apt install dahdi-dkms
[...]
Setting up dkms (2.8.4-3) ...
Setting up linux-headers-5.10.0-8-amd64 (5.10.46-4) ...
/etc/kernel/header_postinst.d/dkms:
dkms: running auto installation service for kernel 5.10.0-8-amd64:.
Setting up dahdi-dkms (1:2.11.1.0.20170917~dfsg-7.4) ...
Loading new dahdi-2.11.1.0.20170917~dfsg-7.4 DKMS files...
Building for 5.10.0-8-amd64
Building initial module for 5.10.0-8-amd64
Done.
dahdi_dummy.ko:
Running module version sanity check.
- Original module
- No original module exists within this kernel
- Installation
- Installing to /lib/modules/5.10.0-8-amd64/updates/dkms/
dahdi_dynamic_eth.ko:
Running module version sanity check.
- Original module
- No original module exists within this kernel
- Installation
- Installing to /lib/modules/5.10.0-8-amd64/updates/dkms/
[...]
DKMS: install completed.
$ sudo dkms status
dahdi, 2.11.1.0.20170917~dfsg-7.4, 5.10.0-8-amd64, x86_64: installed
$ sudo modinfo dahdi_dummy
filename: /lib/modules/5.10.0-8-amd64/updates/dkms/dahdi_dummy.ko
license: GPL v2
author: Robert Pleh <robert.pleh@hermes.si>
description: Timing-Only Driver
depends: dahdi
retpoline: Y
name: dahdi_dummy
vermagic: 5.10.0-8-amd64 SMP mod_unload modversions
parm: debug:int
因為不夠成熟或核心維護者意見不一致，很多功能未列入標準的核心。這種功能就以補丁的型式發行，任何人都可以自由地把它維入核心原始碼。
Debian sometimes provides some of these patches in linux-patch-* packages, but they often don't make it into stable releases (sometimes for the very same reasons that they are not merged into the official upstream kernel). These packages install files in the /usr/src/kernel-patches/ directory.
To apply one or more of these installed patches, use the patch command in the sources directory then start compilation of the kernel as described above. The following shows an old example using linux-patch-grsecurity2 and linux-source-4.9.
$ cd ~/kernel/linux-source-4.9
$ make clean
$ zcat /usr/src/kernel-patches/diffs/grsecurity2/grsecurity-3.1-4.9.11-201702181444.patch.gz | patch -p1
有些補丁不見得適用於每個核心版本；以 patch 可能無法應用於核心原始碼。將出現錯誤訊息且提示錯誤的原因；在此情況下，參照 Debian 補丁套件的文件 (位於 /usr/share/doc/linux-patch-*/ 資料夾)。大部份的情況下，維護者會指出其補丁適用的核心版本。
