1Linux kernel release 4.x <http://kernel.org/>
2=============================================
3
4These are the release notes for Linux version 4.  Read them carefully,
5as they tell you what this is all about, explain how to install the
6kernel, and what to do if something goes wrong.
7
8What is Linux?
9--------------
10
11  Linux is a clone of the operating system Unix, written from scratch by
12  Linus Torvalds with assistance from a loosely-knit team of hackers across
13  the Net. It aims towards POSIX and Single UNIX Specification compliance.
14
15  It has all the features you would expect in a modern fully-fledged Unix,
16  including true multitasking, virtual memory, shared libraries, demand
17  loading, shared copy-on-write executables, proper memory management,
18  and multistack networking including IPv4 and IPv6.
19
20  It is distributed under the GNU General Public License v2 - see the
21  accompanying COPYING file for more details.
22
23On what hardware does it run?
24-----------------------------
25
26  Although originally developed first for 32-bit x86-based PCs (386 or higher),
27  today Linux also runs on (at least) the Compaq Alpha AXP, Sun SPARC and
28  UltraSPARC, Motorola 68000, PowerPC, PowerPC64, ARM, Hitachi SuperH, Cell,
29  IBM S/390, MIPS, HP PA-RISC, Intel IA-64, DEC VAX, AMD x86-64 Xtensa, and
30  ARC architectures.
31
32  Linux is easily portable to most general-purpose 32- or 64-bit architectures
33  as long as they have a paged memory management unit (PMMU) and a port of the
34  GNU C compiler (gcc) (part of The GNU Compiler Collection, GCC). Linux has
35  also been ported to a number of architectures without a PMMU, although
36  functionality is then obviously somewhat limited.
37  Linux has also been ported to itself. You can now run the kernel as a
38  userspace application - this is called UserMode Linux (UML).
39
40Documentation
41-------------
42
43 - There is a lot of documentation available both in electronic form on
44   the Internet and in books, both Linux-specific and pertaining to
45   general UNIX questions.  I'd recommend looking into the documentation
46   subdirectories on any Linux FTP site for the LDP (Linux Documentation
47   Project) books.  This README is not meant to be documentation on the
48   system: there are much better sources available.
49
50 - There are various README files in the Documentation/ subdirectory:
51   these typically contain kernel-specific installation notes for some
52   drivers for example. See Documentation/00-INDEX for a list of what
53   is contained in each file.  Please read the
54   :ref:`Documentation/process/changes.rst <changes>` file, as it
55   contains information about the problems, which may result by upgrading
56   your kernel.
57
58Installing the kernel source
59----------------------------
60
61 - If you install the full sources, put the kernel tarball in a
62   directory where you have permissions (e.g. your home directory) and
63   unpack it::
64
65     xz -cd linux-4.X.tar.xz | tar xvf -
66
67   Replace "X" with the version number of the latest kernel.
68
69   Do NOT use the /usr/src/linux area! This area has a (usually
70   incomplete) set of kernel headers that are used by the library header
71   files.  They should match the library, and not get messed up by
72   whatever the kernel-du-jour happens to be.
73
74 - You can also upgrade between 4.x releases by patching.  Patches are
75   distributed in the xz format.  To install by patching, get all the
76   newer patch files, enter the top level directory of the kernel source
77   (linux-4.X) and execute::
78
79     xz -cd ../patch-4.x.xz | patch -p1
80
81   Replace "x" for all versions bigger than the version "X" of your current
82   source tree, **in_order**, and you should be ok.  You may want to remove
83   the backup files (some-file-name~ or some-file-name.orig), and make sure
84   that there are no failed patches (some-file-name# or some-file-name.rej).
85   If there are, either you or I have made a mistake.
86
87   Unlike patches for the 4.x kernels, patches for the 4.x.y kernels
88   (also known as the -stable kernels) are not incremental but instead apply
89   directly to the base 4.x kernel.  For example, if your base kernel is 4.0
90   and you want to apply the 4.0.3 patch, you must not first apply the 4.0.1
91   and 4.0.2 patches. Similarly, if you are running kernel version 4.0.2 and
92   want to jump to 4.0.3, you must first reverse the 4.0.2 patch (that is,
93   patch -R) **before** applying the 4.0.3 patch. You can read more on this in
94   :ref:`Documentation/process/applying-patches.rst <applying_patches>`.
95
96   Alternatively, the script patch-kernel can be used to automate this
97   process.  It determines the current kernel version and applies any
98   patches found::
99
100     linux/scripts/patch-kernel linux
101
102   The first argument in the command above is the location of the
103   kernel source.  Patches are applied from the current directory, but
104   an alternative directory can be specified as the second argument.
105
106 - Make sure you have no stale .o files and dependencies lying around::
107
108     cd linux
109     make mrproper
110
111   You should now have the sources correctly installed.
112
113Software requirements
114---------------------
115
116   Compiling and running the 4.x kernels requires up-to-date
117   versions of various software packages.  Consult
118   :ref:`Documentation/process/changes.rst <changes>` for the minimum version numbers
119   required and how to get updates for these packages.  Beware that using
120   excessively old versions of these packages can cause indirect
121   errors that are very difficult to track down, so don't assume that
122   you can just update packages when obvious problems arise during
123   build or operation.
124
125Build directory for the kernel
126------------------------------
127
128   When compiling the kernel, all output files will per default be
129   stored together with the kernel source code.
130   Using the option ``make O=output/dir`` allows you to specify an alternate
131   place for the output files (including .config).
132   Example::
133
134     kernel source code: /usr/src/linux-4.X
135     build directory:    /home/name/build/kernel
136
137   To configure and build the kernel, use::
138
139     cd /usr/src/linux-4.X
140     make O=/home/name/build/kernel menuconfig
141     make O=/home/name/build/kernel
142     sudo make O=/home/name/build/kernel modules_install install
143
144   Please note: If the ``O=output/dir`` option is used, then it must be
145   used for all invocations of make.
146
147Configuring the kernel
148----------------------
149
150   Do not skip this step even if you are only upgrading one minor
151   version.  New configuration options are added in each release, and
152   odd problems will turn up if the configuration files are not set up
153   as expected.  If you want to carry your existing configuration to a
154   new version with minimal work, use ``make oldconfig``, which will
155   only ask you for the answers to new questions.
156
157 - Alternative configuration commands are::
158
159     "make config"      Plain text interface.
160
161     "make menuconfig"  Text based color menus, radiolists & dialogs.
162
163     "make nconfig"     Enhanced text based color menus.
164
165     "make xconfig"     Qt based configuration tool.
166
167     "make gconfig"     GTK+ based configuration tool.
168
169     "make oldconfig"   Default all questions based on the contents of
170                        your existing ./.config file and asking about
171                        new config symbols.
172
173     "make olddefconfig"
174                        Like above, but sets new symbols to their default
175                        values without prompting.
176
177     "make defconfig"   Create a ./.config file by using the default
178                        symbol values from either arch/$ARCH/defconfig
179                        or arch/$ARCH/configs/${PLATFORM}_defconfig,
180                        depending on the architecture.
181
182     "make ${PLATFORM}_defconfig"
183                        Create a ./.config file by using the default
184                        symbol values from
185                        arch/$ARCH/configs/${PLATFORM}_defconfig.
186                        Use "make help" to get a list of all available
187                        platforms of your architecture.
188
189     "make allyesconfig"
190                        Create a ./.config file by setting symbol
191                        values to 'y' as much as possible.
192
193     "make allmodconfig"
194                        Create a ./.config file by setting symbol
195                        values to 'm' as much as possible.
196
197     "make allnoconfig" Create a ./.config file by setting symbol
198                        values to 'n' as much as possible.
199
200     "make randconfig"  Create a ./.config file by setting symbol
201                        values to random values.
202
203     "make localmodconfig" Create a config based on current config and
204                           loaded modules (lsmod). Disables any module
205                           option that is not needed for the loaded modules.
206
207                           To create a localmodconfig for another machine,
208                           store the lsmod of that machine into a file
209                           and pass it in as a LSMOD parameter.
210
211                   target$ lsmod > /tmp/mylsmod
212                   target$ scp /tmp/mylsmod host:/tmp
213
214                   host$ make LSMOD=/tmp/mylsmod localmodconfig
215
216                           The above also works when cross compiling.
217
218     "make localyesconfig" Similar to localmodconfig, except it will convert
219                           all module options to built in (=y) options.
220
221     "make kvmconfig"   Enable additional options for kvm guest kernel support.
222
223     "make xenconfig"   Enable additional options for xen dom0 guest kernel
224                        support.
225
226     "make tinyconfig"  Configure the tiniest possible kernel.
227
228   You can find more information on using the Linux kernel config tools
229   in Documentation/kbuild/kconfig.txt.
230
231 - NOTES on ``make config``:
232
233    - Having unnecessary drivers will make the kernel bigger, and can
234      under some circumstances lead to problems: probing for a
235      nonexistent controller card may confuse your other controllers.
236
237    - A kernel with math-emulation compiled in will still use the
238      coprocessor if one is present: the math emulation will just
239      never get used in that case.  The kernel will be slightly larger,
240      but will work on different machines regardless of whether they
241      have a math coprocessor or not.
242
243    - The "kernel hacking" configuration details usually result in a
244      bigger or slower kernel (or both), and can even make the kernel
245      less stable by configuring some routines to actively try to
246      break bad code to find kernel problems (kmalloc()).  Thus you
247      should probably answer 'n' to the questions for "development",
248      "experimental", or "debugging" features.
249
250Compiling the kernel
251--------------------
252
253 - Make sure you have at least gcc 3.2 available.
254   For more information, refer to :ref:`Documentation/process/changes.rst <changes>`.
255
256   Please note that you can still run a.out user programs with this kernel.
257
258 - Do a ``make`` to create a compressed kernel image. It is also
259   possible to do ``make install`` if you have lilo installed to suit the
260   kernel makefiles, but you may want to check your particular lilo setup first.
261
262   To do the actual install, you have to be root, but none of the normal
263   build should require that. Don't take the name of root in vain.
264
265 - If you configured any of the parts of the kernel as ``modules``, you
266   will also have to do ``make modules_install``.
267
268 - Verbose kernel compile/build output:
269
270   Normally, the kernel build system runs in a fairly quiet mode (but not
271   totally silent).  However, sometimes you or other kernel developers need
272   to see compile, link, or other commands exactly as they are executed.
273   For this, use "verbose" build mode.  This is done by passing
274   ``V=1`` to the ``make`` command, e.g.::
275
276     make V=1 all
277
278   To have the build system also tell the reason for the rebuild of each
279   target, use ``V=2``.  The default is ``V=0``.
280
281 - Keep a backup kernel handy in case something goes wrong.  This is
282   especially true for the development releases, since each new release
283   contains new code which has not been debugged.  Make sure you keep a
284   backup of the modules corresponding to that kernel, as well.  If you
285   are installing a new kernel with the same version number as your
286   working kernel, make a backup of your modules directory before you
287   do a ``make modules_install``.
288
289   Alternatively, before compiling, use the kernel config option
290   "LOCALVERSION" to append a unique suffix to the regular kernel version.
291   LOCALVERSION can be set in the "General Setup" menu.
292
293 - In order to boot your new kernel, you'll need to copy the kernel
294   image (e.g. .../linux/arch/x86/boot/bzImage after compilation)
295   to the place where your regular bootable kernel is found.
296
297 - Booting a kernel directly from a floppy without the assistance of a
298   bootloader such as LILO, is no longer supported.
299
300   If you boot Linux from the hard drive, chances are you use LILO, which
301   uses the kernel image as specified in the file /etc/lilo.conf.  The
302   kernel image file is usually /vmlinuz, /boot/vmlinuz, /bzImage or
303   /boot/bzImage.  To use the new kernel, save a copy of the old image
304   and copy the new image over the old one.  Then, you MUST RERUN LILO
305   to update the loading map! If you don't, you won't be able to boot
306   the new kernel image.
307
308   Reinstalling LILO is usually a matter of running /sbin/lilo.
309   You may wish to edit /etc/lilo.conf to specify an entry for your
310   old kernel image (say, /vmlinux.old) in case the new one does not
311   work.  See the LILO docs for more information.
312
313   After reinstalling LILO, you should be all set.  Shutdown the system,
314   reboot, and enjoy!
315
316   If you ever need to change the default root device, video mode,
317   ramdisk size, etc.  in the kernel image, use the ``rdev`` program (or
318   alternatively the LILO boot options when appropriate).  No need to
319   recompile the kernel to change these parameters.
320
321 - Reboot with the new kernel and enjoy.
322
323If something goes wrong
324-----------------------
325
326 - If you have problems that seem to be due to kernel bugs, please check
327   the file MAINTAINERS to see if there is a particular person associated
328   with the part of the kernel that you are having trouble with. If there
329   isn't anyone listed there, then the second best thing is to mail
330   them to me (torvalds@linux-foundation.org), and possibly to any other
331   relevant mailing-list or to the newsgroup.
332
333 - In all bug-reports, *please* tell what kernel you are talking about,
334   how to duplicate the problem, and what your setup is (use your common
335   sense).  If the problem is new, tell me so, and if the problem is
336   old, please try to tell me when you first noticed it.
337
338 - If the bug results in a message like::
339
340     unable to handle kernel paging request at address C0000010
341     Oops: 0002
342     EIP:   0010:XXXXXXXX
343     eax: xxxxxxxx   ebx: xxxxxxxx   ecx: xxxxxxxx   edx: xxxxxxxx
344     esi: xxxxxxxx   edi: xxxxxxxx   ebp: xxxxxxxx
345     ds: xxxx  es: xxxx  fs: xxxx  gs: xxxx
346     Pid: xx, process nr: xx
347     xx xx xx xx xx xx xx xx xx xx
348
349   or similar kernel debugging information on your screen or in your
350   system log, please duplicate it *exactly*.  The dump may look
351   incomprehensible to you, but it does contain information that may
352   help debugging the problem.  The text above the dump is also
353   important: it tells something about why the kernel dumped code (in
354   the above example, it's due to a bad kernel pointer). More information
355   on making sense of the dump is in Documentation/admin-guide/bug-hunting.rst
356
357 - If you compiled the kernel with CONFIG_KALLSYMS you can send the dump
358   as is, otherwise you will have to use the ``ksymoops`` program to make
359   sense of the dump (but compiling with CONFIG_KALLSYMS is usually preferred).
360   This utility can be downloaded from
361   https://www.kernel.org/pub/linux/utils/kernel/ksymoops/ .
362   Alternatively, you can do the dump lookup by hand:
363
364 - In debugging dumps like the above, it helps enormously if you can
365   look up what the EIP value means.  The hex value as such doesn't help
366   me or anybody else very much: it will depend on your particular
367   kernel setup.  What you should do is take the hex value from the EIP
368   line (ignore the ``0010:``), and look it up in the kernel namelist to
369   see which kernel function contains the offending address.
370
371   To find out the kernel function name, you'll need to find the system
372   binary associated with the kernel that exhibited the symptom.  This is
373   the file 'linux/vmlinux'.  To extract the namelist and match it against
374   the EIP from the kernel crash, do::
375
376     nm vmlinux | sort | less
377
378   This will give you a list of kernel addresses sorted in ascending
379   order, from which it is simple to find the function that contains the
380   offending address.  Note that the address given by the kernel
381   debugging messages will not necessarily match exactly with the
382   function addresses (in fact, that is very unlikely), so you can't
383   just 'grep' the list: the list will, however, give you the starting
384   point of each kernel function, so by looking for the function that
385   has a starting address lower than the one you are searching for but
386   is followed by a function with a higher address you will find the one
387   you want.  In fact, it may be a good idea to include a bit of
388   "context" in your problem report, giving a few lines around the
389   interesting one.
390
391   If you for some reason cannot do the above (you have a pre-compiled
392   kernel image or similar), telling me as much about your setup as
393   possible will help.  Please read the :ref:`admin-guide/reporting-bugs.rst <reportingbugs>`
394   document for details.
395
396 - Alternatively, you can use gdb on a running kernel. (read-only; i.e. you
397   cannot change values or set break points.) To do this, first compile the
398   kernel with -g; edit arch/x86/Makefile appropriately, then do a ``make
399   clean``. You'll also need to enable CONFIG_PROC_FS (via ``make config``).
400
401   After you've rebooted with the new kernel, do ``gdb vmlinux /proc/kcore``.
402   You can now use all the usual gdb commands. The command to look up the
403   point where your system crashed is ``l *0xXXXXXXXX``. (Replace the XXXes
404   with the EIP value.)
405
406   gdb'ing a non-running kernel currently fails because ``gdb`` (wrongly)
407   disregards the starting offset for which the kernel is compiled.
408