Documentation/admin-guide/README.rst

3 Linux kernel release 6.x <http://kernel.org/>
8 kernel, and what to do if something goes wrong.
11 --------------
14   Linus Torvalds with assistance from a loosely-knit team of hackers across
17   It has all the features you would expect in a modern fully-fledged Unix,
19   loading, shared copy-on-write executables, proper memory management,
22   It is distributed under the GNU General Public License v2 - see the
26 -----------------------------
28   Although originally developed first for 32-bit x86-based PCs (386 or higher),
31   IBM S/390, MIPS, HP PA-RISC, Intel IA-64, DEC VAX, AMD x86-64 Xtensa, and
34   Linux is easily portable to most general-purpose 32- or 64-bit architectures
39   Linux has also been ported to itself. You can now run the kernel as a
40   userspace application - this is called UserMode Linux (UML).
43 -------------
45  - There is a lot of documentation available both in electronic form on
46    the Internet and in books, both Linux-specific and pertaining to
52  - There are various README files in the Documentation/ subdirectory:
53    these typically contain kernel-specific installation notes for some
57    your kernel.
59 Installing the kernel source
60 ----------------------------
62  - If you install the full sources, put the kernel tarball in a
66      xz -cd linux-6.x.tar.xz | tar xvf -
68    Replace "X" with the version number of the latest kernel.
71    incomplete) set of kernel headers that are used by the library header
73    whatever the kernel-du-jour happens to be.
75  - You can also upgrade between 6.x releases by patching.  Patches are
76    distributed in the xz format.  To install by patching, get all the
77    newer patch files, enter the top level directory of the kernel source
78    (linux-6.x) and execute::
80      xz -cd ../patch-6.x.xz | patch -p1
84    the backup files (some-file-name~ or some-file-name.orig), and make sure
85    that there are no failed patches (some-file-name# or some-file-name.rej).
89    (also known as the -stable kernels) are not incremental but instead apply
90    directly to the base 6.x kernel.  For example, if your base kernel is 6.0
92    and 6.0.2 patches. Similarly, if you are running kernel version 6.0.2 and
94    patch -R) **before** applying the 6.0.3 patch. You can read more on this in
95    :ref:`Documentation/process/applying-patches.rst <applying_patches>`.
97    Alternatively, the script patch-kernel can be used to automate this
98    process.  It determines the current kernel version and applies any
101      linux/scripts/patch-kernel linux
103    The first argument in the command above is the location of the
104    kernel source.  Patches are applied from the current directory, but
107  - Make sure you have no stale .o files and dependencies lying around::
115 ---------------------
117    Compiling and running the 6.x kernels requires up-to-date
126 Build directory for the kernel
127 ------------------------------
129    When compiling the kernel, all output files will per default be
130    stored together with the kernel source code.
135      kernel source code: /usr/src/linux-6.x
136      build directory:    /home/name/build/kernel
138    To configure and build the kernel, use::
140      cd /usr/src/linux-6.x
141      make O=/home/name/build/kernel menuconfig
142      make O=/home/name/build/kernel
143      sudo make O=/home/name/build/kernel modules_install install
148 Configuring the kernel
149 ----------------------
152    version.  New configuration options are added in each release, and
158  - Alternative configuration commands are::
210                            and pass it in as a LSMOD parameter.
212                            Also, you can preserve modules in certain folders
213                            or kconfig files by specifying their paths in
226                            all module options to built in (=y) options. You can
229      "make kvm_guest.config"   Enable additional options for kvm guest kernel
232      "make xen.config"   Enable additional options for xen dom0 guest kernel
235      "make tinyconfig"  Configure the tiniest possible kernel.
237    You can find more information on using the Linux kernel config tools
238    in Documentation/kbuild/kconfig.rst.
240  - NOTES on ``make config``:
242     - Having unnecessary drivers will make the kernel bigger, and can
246     - A kernel with math-emulation compiled in will still use the
248       never get used in that case.  The kernel will be slightly larger,
252     - The "kernel hacking" configuration details usually result in a
253       bigger or slower kernel (or both), and can even make the kernel
255       break bad code to find kernel problems (kmalloc()).  Thus you
259 Compiling the kernel
260 --------------------
262  - Make sure you have at least gcc 5.1 available.
265  - Do a ``make`` to create a compressed kernel image. It is also possible to do
267    install script recognised by the kernel's installer. Most popular
272    build should require that. Don't take the name of root in vain.
274  - If you configured any of the parts of the kernel as ``modules``, you
277  - Verbose kernel compile/build output:
279    Normally, the kernel build system runs in a fairly quiet mode (but not
280    totally silent).  However, sometimes you or other kernel developers need
290  - Keep a backup kernel handy in case something goes wrong.  This is
293    backup of the modules corresponding to that kernel, as well.  If you
294    are installing a new kernel with the same version number as your
295    working kernel, make a backup of your modules directory before you
298    Alternatively, before compiling, use the kernel config option
299    "LOCALVERSION" to append a unique suffix to the regular kernel version.
300    LOCALVERSION can be set in the "General Setup" menu.
302  - In order to boot your new kernel, you'll need to copy the kernel
304    to the place where your regular bootable kernel is found.
306  - Booting a kernel directly from a storage device without the assistance
307    of a bootloader such as LILO or GRUB, is no longer supported in BIOS
308    (non-EFI systems). On UEFI/EFI systems, however, you can use EFISTUB
309    which allows the motherboard to boot directly to the kernel.
313    see "Documentation/admin-guide/efi-stub.rst".
315  - It's important to note that as of 2016 LILO (LInux LOader) is no longer in
317    in documentation. Popular alternatives include GRUB2, rEFInd, Syslinux,
318    systemd-boot, or EFISTUB. For various reasons, it's not recommended to use
319    software that's no longer in active development.
321  - Chances are your distribution includes an install script and running
327 ------------------------
330  - If you use LILO the kernel images are specified in the file /etc/lilo.conf.
331    The kernel image file is usually /vmlinuz, /boot/vmlinuz, /bzImage or
332    /boot/bzImage. To use the new kernel, save a copy of the old image and copy
334    loading map! If you don't, you won't be able to boot the new kernel image.
336  - Reinstalling LILO is usually a matter of running /sbin/lilo. You may wish
337    to edit /etc/lilo.conf to specify an entry for your old kernel image
338    (say, /vmlinux.old) in case the new one does not work. See the LILO docs
341  - After reinstalling LILO, you should be all set. Shutdown the system,
344  - If you ever need to change the default root device, video mode, etc. in the
345    kernel image, use your bootloader's boot options where appropriate. No need
346    to recompile the kernel to change these parameters.
348  - Reboot with the new kernel and enjoy.
352 -----------------------
354 If you have problems that seem to be due to kernel bugs, please follow the
355 instructions at 'Documentation/admin-guide/reporting-issues.rst'.
357 Hints on understanding kernel bug reports are in
358 'Documentation/admin-guide/bug-hunting.rst'. More on debugging the kernel
359 with gdb is in 'Documentation/dev-tools/gdb-kernel-debugging.rst' and
360 'Documentation/dev-tools/kgdb.rst'.