1 .. _readme:
2
3 Linux kernel release 6.x <http://kernel.org/>
4 =============================================
5
6 These are the release notes for Linux version 6. Read them carefully,
7 as they tell you what this is all about, explain how to install the
8 kernel, and what to do if something goes wrong.
9
10 What is Linux?
11 --------------
12
13 Linux is a clone of the operating system Unix, written from scratch by
14 Linus Torvalds with assistance from a loosely-knit team of hackers across
15 the Net. It aims towards POSIX and Single UNIX Specification compliance.
16
17 It has all the features you would expect in a modern fully-fledged Unix,
18 including true multitasking, virtual memory, shared libraries, demand
19 loading, shared copy-on-write executables, proper memory management,
20 and multistack networking including IPv4 and IPv6.
21
22 It is distributed under the GNU General Public License v2 - see the
23 accompanying COPYING file for more details.
24
25 On what hardware does it run?
26 -----------------------------
27
28 Although originally developed first for 32-bit x86-based PCs (386 or higher),
29 today Linux also runs on (at least) the Compaq Alpha AXP, Sun SPARC and
30 UltraSPARC, Motorola 68000, PowerPC, PowerPC64, ARM, Hitachi SuperH, Cell,
31 IBM S/390, MIPS, HP PA-RISC, Intel IA-64, DEC VAX, AMD x86-64 Xtensa, and
32 ARC architectures.
33
34 Linux is easily portable to most general-purpose 32- or 64-bit architectures
35 as long as they have a paged memory management unit (PMMU) and a port of the
36 GNU C compiler (gcc) (part of The GNU Compiler Collection, GCC). Linux has
37 also been ported to a number of architectures without a PMMU, although
38 functionality is then obviously somewhat limited.
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).
41
42 Documentation
43 -------------
44
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
47 general UNIX questions. I'd recommend looking into the documentation
48 subdirectories on any Linux FTP site for the LDP (Linux Documentation
49 Project) books. This README is not meant to be documentation on the
50 system: there are much better sources available.
51
52 - There are various README files in the Documentation/ subdirectory:
53 these typically contain kernel-specific installation notes for some
54 drivers for example. Please read the
55 :ref:`Documentation/process/changes.rst <changes>` file, as it
56 contains information about the problems, which may result by upgrading
57 your kernel.
58
59 Installing the kernel source
60 ----------------------------
61
62 - If you install the full sources, put the kernel tarball in a
63 directory where you have permissions (e.g. your home directory) and
64 unpack it::
65
66 xz -cd linux-6.x.tar.xz | tar xvf -
67
68 Replace "X" with the version number of the latest kernel.
69
70 Do NOT use the /usr/src/linux area! This area has a (usually
71 incomplete) set of kernel headers that are used by the library header
72 files. They should match the library, and not get messed up by
73 whatever the kernel-du-jour happens to be.
74
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::
79
80 xz -cd ../patch-6.x.xz | patch -p1
81
82 Replace "x" for all versions bigger than the version "x" of your current
83 source tree, **in_order**, and you should be ok. You may want to remove
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).
86 If there are, either you or I have made a mistake.
87
88 Unlike patches for the 6.x kernels, patches for the 6.x.y kernels
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
91 and you want to apply the 6.0.3 patch, you must not first apply the 6.0.1
92 and 6.0.2 patches. Similarly, if you are running kernel version 6.0.2 and
93 want to jump to 6.0.3, you must first reverse the 6.0.2 patch (that is,
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>`.
96
97 Alternatively, the script patch-kernel can be used to automate this
98 process. It determines the current kernel version and applies any
99 patches found::
100
101 linux/scripts/patch-kernel linux
102
103 The first argument in the command above is the location of the
104 kernel source. Patches are applied from the current directory, but
105 an alternative directory can be specified as the second argument.
106
107 - Make sure you have no stale .o files and dependencies lying around::
108
109 cd linux
110 make mrproper
111
112 You should now have the sources correctly installed.
113
114 Software requirements
115 ---------------------
116
117 Compiling and running the 6.x kernels requires up-to-date
118 versions of various software packages. Consult
119 :ref:`Documentation/process/changes.rst <changes>` for the minimum version numbers
120 required and how to get updates for these packages. Beware that using
121 excessively old versions of these packages can cause indirect
122 errors that are very difficult to track down, so don't assume that
123 you can just update packages when obvious problems arise during
124 build or operation.
125
126 Build directory for the kernel
127 ------------------------------
128
129 When compiling the kernel, all output files will per default be
130 stored together with the kernel source code.
131 Using the option ``make O=output/dir`` allows you to specify an alternate
132 place for the output files (including .config).
133 Example::
134
135 kernel source code: /usr/src/linux-6.x
136 build directory: /home/name/build/kernel
137
138 To configure and build the kernel, use::
139
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
144
145 Please note: If the ``O=output/dir`` option is used, then it must be
146 used for all invocations of make.
147
148 Configuring the kernel
149 ----------------------
150
151 Do not skip this step even if you are only upgrading one minor
152 version. New configuration options are added in each release, and
153 odd problems will turn up if the configuration files are not set up
154 as expected. If you want to carry your existing configuration to a
155 new version with minimal work, use ``make oldconfig``, which will
156 only ask you for the answers to new questions.
157
158 - Alternative configuration commands are::
159
160 "make config" Plain text interface.
161
162 "make menuconfig" Text based color menus, radiolists & dialogs.
163
164 "make nconfig" Enhanced text based color menus.
165
166 "make xconfig" Qt based configuration tool.
167
168 "make gconfig" GTK+ based configuration tool.
169
170 "make oldconfig" Default all questions based on the contents of
171 your existing ./.config file and asking about
172 new config symbols.
173
174 "make olddefconfig"
175 Like above, but sets new symbols to their default
176 values without prompting.
177
178 "make defconfig" Create a ./.config file by using the default
179 symbol values from either arch/$ARCH/defconfig
180 or arch/$ARCH/configs/${PLATFORM}_defconfig,
181 depending on the architecture.
182
183 "make ${PLATFORM}_defconfig"
184 Create a ./.config file by using the default
185 symbol values from
186 arch/$ARCH/configs/${PLATFORM}_defconfig.
187 Use "make help" to get a list of all available
188 platforms of your architecture.
189
190 "make allyesconfig"
191 Create a ./.config file by setting symbol
192 values to 'y' as much as possible.
193
194 "make allmodconfig"
195 Create a ./.config file by setting symbol
196 values to 'm' as much as possible.
197
198 "make allnoconfig" Create a ./.config file by setting symbol
199 values to 'n' as much as possible.
200
201 "make randconfig" Create a ./.config file by setting symbol
202 values to random values.
203
204 "make localmodconfig" Create a config based on current config and
205 loaded modules (lsmod). Disables any module
206 option that is not needed for the loaded modules.
207
208 To create a localmodconfig for another machine,
209 store the lsmod of that machine into a file
210 and pass it in as a LSMOD parameter.
211
212 Also, you can preserve modules in certain folders
213 or kconfig files by specifying their paths in
214 parameter LMC_KEEP.
215
216 target$ lsmod > /tmp/mylsmod
217 target$ scp /tmp/mylsmod host:/tmp
218
219 host$ make LSMOD=/tmp/mylsmod \
220 LMC_KEEP="drivers/usb:drivers/gpu:fs" \
221 localmodconfig
222
223 The above also works when cross compiling.
224
225 "make localyesconfig" Similar to localmodconfig, except it will convert
226 all module options to built in (=y) options. You can
227 also preserve modules by LMC_KEEP.
228
229 "make kvm_guest.config" Enable additional options for kvm guest kernel
230 support.
231
232 "make xen.config" Enable additional options for xen dom0 guest kernel
233 support.
234
235 "make tinyconfig" Configure the tiniest possible kernel.
236
237 You can find more information on using the Linux kernel config tools
238 in Documentation/kbuild/kconfig.rst.
239
240 - NOTES on ``make config``:
241
242 - Having unnecessary drivers will make the kernel bigger, and can
243 under some circumstances lead to problems: probing for a
244 nonexistent controller card may confuse your other controllers.
245
246 - A kernel with math-emulation compiled in will still use the
247 coprocessor if one is present: the math emulation will just
248 never get used in that case. The kernel will be slightly larger,
249 but will work on different machines regardless of whether they
250 have a math coprocessor or not.
251
252 - The "kernel hacking" configuration details usually result in a
253 bigger or slower kernel (or both), and can even make the kernel
254 less stable by configuring some routines to actively try to
255 break bad code to find kernel problems (kmalloc()). Thus you
256 should probably answer 'n' to the questions for "development",
257 "experimental", or "debugging" features.
258
259 Compiling the kernel
260 --------------------
261
262 - Make sure you have at least gcc 5.1 available.
263 For more information, refer to :ref:`Documentation/process/changes.rst <changes>`.
264
265 - Do a ``make`` to create a compressed kernel image. It is also possible to do
266 ``make install`` if you have lilo installed or if your distribution has an
267 install script recognised by the kernel's installer. Most popular
268 distributions will have a recognized install script. You may want to
269 check your distribution's setup first.
270
271 To do the actual install, you have to be root, but none of the normal
272 build should require that. Don't take the name of root in vain.
273
274 - If you configured any of the parts of the kernel as ``modules``, you
275 will also have to do ``make modules_install``.
276
277 - Verbose kernel compile/build output:
278
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
281 to see compile, link, or other commands exactly as they are executed.
282 For this, use "verbose" build mode. This is done by passing
283 ``V=1`` to the ``make`` command, e.g.::
284
285 make V=1 all
286
287 To have the build system also tell the reason for the rebuild of each
288 target, use ``V=2``. The default is ``V=0``.
289
290 - Keep a backup kernel handy in case something goes wrong. This is
291 especially true for the development releases, since each new release
292 contains new code which has not been debugged. Make sure you keep a
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
296 do a ``make modules_install``.
297
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.
301
302 - In order to boot your new kernel, you'll need to copy the kernel
303 image (e.g. .../linux/arch/x86/boot/bzImage after compilation)
304 to the place where your regular bootable kernel is found.
305
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.
310 On modern workstations and desktops, it's generally recommended to use a
311 bootloader as difficulties can arise with multiple kernels and secure boot.
312 For more details on EFISTUB,
313 see "Documentation/admin-guide/efi-stub.rst".
314
315 - It's important to note that as of 2016 LILO (LInux LOader) is no longer in
316 active development, though as it was extremely popular, it often comes up
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.
320
321 - Chances are your distribution includes an install script and running
322 ``make install`` will be all that's needed. Should that not be the case
323 you'll have to identify your bootloader and reference its documentation or
324 configure your EFI.
325
326 Legacy LILO Instructions
327 ------------------------
328
329
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
333 the new image over the old one. Then, you MUST RERUN LILO to update the
334 loading map! If you don't, you won't be able to boot the new kernel image.
335
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
339 for more information.
340
341 - After reinstalling LILO, you should be all set. Shutdown the system,
342 reboot, and enjoy!
343
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.
347
348 - Reboot with the new kernel and enjoy.
349
350
351 If something goes wrong
352 -----------------------
353
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'.
356
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'.
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.