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README

1        Linux kernel release 4.x <http://kernel.org/>
2
3These are the release notes for Linux version 4.  Read them carefully,
4as they tell you what this is all about, explain how to install the
5kernel, and what to do if something goes wrong.
6
7WHAT IS LINUX?
8
9  Linux is a clone of the operating system Unix, written from scratch by
10  Linus Torvalds with assistance from a loosely-knit team of hackers across
11  the Net. It aims towards POSIX and Single UNIX Specification compliance.
12
13  It has all the features you would expect in a modern fully-fledged Unix,
14  including true multitasking, virtual memory, shared libraries, demand
15  loading, shared copy-on-write executables, proper memory management,
16  and multistack networking including IPv4 and IPv6.
17
18  It is distributed under the GNU General Public License - see the
19  accompanying COPYING file for more details.
20
21ON WHAT HARDWARE DOES IT RUN?
22
23  Although originally developed first for 32-bit x86-based PCs (386 or higher),
24  today Linux also runs on (at least) the Compaq Alpha AXP, Sun SPARC and
25  UltraSPARC, Motorola 68000, PowerPC, PowerPC64, ARM, Hitachi SuperH, Cell,
26  IBM S/390, MIPS, HP PA-RISC, Intel IA-64, DEC VAX, AMD x86-64, AXIS CRIS,
27  Xtensa, Tilera TILE, AVR32, ARC and Renesas M32R architectures.
28
29  Linux is easily portable to most general-purpose 32- or 64-bit architectures
30  as long as they have a paged memory management unit (PMMU) and a port of the
31  GNU C compiler (gcc) (part of The GNU Compiler Collection, GCC). Linux has
32  also been ported to a number of architectures without a PMMU, although
33  functionality is then obviously somewhat limited.
34  Linux has also been ported to itself. You can now run the kernel as a
35  userspace application - this is called UserMode Linux (UML).
36
37DOCUMENTATION:
38
39 - There is a lot of documentation available both in electronic form on
40   the Internet and in books, both Linux-specific and pertaining to
41   general UNIX questions.  I'd recommend looking into the documentation
42   subdirectories on any Linux FTP site for the LDP (Linux Documentation
43   Project) books.  This README is not meant to be documentation on the
44   system: there are much better sources available.
45
46 - There are various README files in the Documentation/ subdirectory:
47   these typically contain kernel-specific installation notes for some
48   drivers for example. See Documentation/00-INDEX for a list of what
49   is contained in each file.  Please read the Changes file, as it
50   contains information about the problems, which may result by upgrading
51   your kernel.
52
53 - The Documentation/DocBook/ subdirectory contains several guides for
54   kernel developers and users.  These guides can be rendered in a
55   number of formats:  PostScript (.ps), PDF, HTML, & man-pages, among others.
56   After installation, "make psdocs", "make pdfdocs", "make htmldocs",
57   or "make mandocs" will render the documentation in the requested format.
58
59INSTALLING the kernel source:
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   Documentation/applying-patches.txt
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   Compiling and running the 4.x kernels requires up-to-date
116   versions of various software packages.  Consult
117   Documentation/Changes for the minimum version numbers required
118   and how to get updates for these packages.  Beware that using
119   excessively old versions of these packages can cause indirect
120   errors that are very difficult to track down, so don't assume that
121   you can just update packages when obvious problems arise during
122   build or operation.
123
124BUILD directory for the kernel:
125
126   When compiling the kernel, all output files will per default be
127   stored together with the kernel source code.
128   Using the option "make O=output/dir" allows you to specify an alternate
129   place for the output files (including .config).
130   Example:
131
132     kernel source code: /usr/src/linux-4.X
133     build directory:    /home/name/build/kernel
134
135   To configure and build the kernel, use:
136
137     cd /usr/src/linux-4.X
138     make O=/home/name/build/kernel menuconfig
139     make O=/home/name/build/kernel
140     sudo make O=/home/name/build/kernel modules_install install
141
142   Please note: If the 'O=output/dir' option is used, then it must be
143   used for all invocations of make.
144
145CONFIGURING the kernel:
146
147   Do not skip this step even if you are only upgrading one minor
148   version.  New configuration options are added in each release, and
149   odd problems will turn up if the configuration files are not set up
150   as expected.  If you want to carry your existing configuration to a
151   new version with minimal work, use "make oldconfig", which will
152   only ask you for the answers to new questions.
153
154 - Alternative configuration commands are:
155
156     "make config"      Plain text interface.
157
158     "make menuconfig"  Text based color menus, radiolists & dialogs.
159
160     "make nconfig"     Enhanced text based color menus.
161
162     "make xconfig"     Qt based configuration tool.
163
164     "make gconfig"     GTK+ based configuration tool.
165
166     "make oldconfig"   Default all questions based on the contents of
167                        your existing ./.config file and asking about
168                        new config symbols.
169
170     "make silentoldconfig"
171                        Like above, but avoids cluttering the screen
172                        with questions already answered.
173                        Additionally updates the dependencies.
174
175     "make olddefconfig"
176                        Like above, but sets new symbols to their default
177                        values without prompting.
178
179     "make defconfig"   Create a ./.config file by using the default
180                        symbol values from either arch/$ARCH/defconfig
181                        or arch/$ARCH/configs/${PLATFORM}_defconfig,
182                        depending on the architecture.
183
184     "make ${PLATFORM}_defconfig"
185                        Create a ./.config file by using the default
186                        symbol values from
187                        arch/$ARCH/configs/${PLATFORM}_defconfig.
188                        Use "make help" to get a list of all available
189                        platforms of your architecture.
190
191     "make allyesconfig"
192                        Create a ./.config file by setting symbol
193                        values to 'y' as much as possible.
194
195     "make allmodconfig"
196                        Create a ./.config file by setting symbol
197                        values to 'm' as much as possible.
198
199     "make allnoconfig" Create a ./.config file by setting symbol
200                        values to 'n' as much as possible.
201
202     "make randconfig"  Create a ./.config file by setting symbol
203                        values to random values.
204
205     "make localmodconfig" Create a config based on current config and
206                           loaded modules (lsmod). Disables any module
207                           option that is not needed for the loaded modules.
208
209                           To create a localmodconfig for another machine,
210                           store the lsmod of that machine into a file
211                           and pass it in as a LSMOD parameter.
212
213                   target$ lsmod > /tmp/mylsmod
214                   target$ scp /tmp/mylsmod host:/tmp
215
216                   host$ make LSMOD=/tmp/mylsmod localmodconfig
217
218                           The above also works when cross compiling.
219
220     "make localyesconfig" Similar to localmodconfig, except it will convert
221                           all module options to built in (=y) options.
222
223   You can find more information on using the Linux kernel config tools
224   in Documentation/kbuild/kconfig.txt.
225
226 - NOTES on "make config":
227
228    - Having unnecessary drivers will make the kernel bigger, and can
229      under some circumstances lead to problems: probing for a
230      nonexistent controller card may confuse your other controllers
231
232    - Compiling the kernel with "Processor type" set higher than 386
233      will result in a kernel that does NOT work on a 386.  The
234      kernel will detect this on bootup, and give up.
235
236    - A kernel with math-emulation compiled in will still use the
237      coprocessor if one is present: the math emulation will just
238      never get used in that case.  The kernel will be slightly larger,
239      but will work on different machines regardless of whether they
240      have a math coprocessor or not.
241
242    - The "kernel hacking" configuration details usually result in a
243      bigger or slower kernel (or both), and can even make the kernel
244      less stable by configuring some routines to actively try to
245      break bad code to find kernel problems (kmalloc()).  Thus you
246      should probably answer 'n' to the questions for "development",
247      "experimental", or "debugging" features.
248
249COMPILING the kernel:
250
251 - Make sure you have at least gcc 3.2 available.
252   For more information, refer to Documentation/Changes.
253
254   Please note that you can still run a.out user programs with this kernel.
255
256 - Do a "make" to create a compressed kernel image. It is also
257   possible to do "make install" if you have lilo installed to suit the
258   kernel makefiles, but you may want to check your particular lilo setup first.
259
260   To do the actual install, you have to be root, but none of the normal
261   build should require that. Don't take the name of root in vain.
262
263 - If you configured any of the parts of the kernel as `modules', you
264   will also have to do "make modules_install".
265
266 - Verbose kernel compile/build output:
267
268   Normally, the kernel build system runs in a fairly quiet mode (but not
269   totally silent).  However, sometimes you or other kernel developers need
270   to see compile, link, or other commands exactly as they are executed.
271   For this, use "verbose" build mode.  This is done by passing
272   "V=1" to the "make" command, e.g.
273
274     make V=1 all
275
276   To have the build system also tell the reason for the rebuild of each
277   target, use "V=2".  The default is "V=0".
278
279 - Keep a backup kernel handy in case something goes wrong.  This is
280   especially true for the development releases, since each new release
281   contains new code which has not been debugged.  Make sure you keep a
282   backup of the modules corresponding to that kernel, as well.  If you
283   are installing a new kernel with the same version number as your
284   working kernel, make a backup of your modules directory before you
285   do a "make modules_install".
286
287   Alternatively, before compiling, use the kernel config option
288   "LOCALVERSION" to append a unique suffix to the regular kernel version.
289   LOCALVERSION can be set in the "General Setup" menu.
290
291 - In order to boot your new kernel, you'll need to copy the kernel
292   image (e.g. .../linux/arch/i386/boot/bzImage after compilation)
293   to the place where your regular bootable kernel is found.
294
295 - Booting a kernel directly from a floppy without the assistance of a
296   bootloader such as LILO, is no longer supported.
297
298   If you boot Linux from the hard drive, chances are you use LILO, which
299   uses the kernel image as specified in the file /etc/lilo.conf.  The
300   kernel image file is usually /vmlinuz, /boot/vmlinuz, /bzImage or
301   /boot/bzImage.  To use the new kernel, save a copy of the old image
302   and copy the new image over the old one.  Then, you MUST RERUN LILO
303   to update the loading map! If you don't, you won't be able to boot
304   the new kernel image.
305
306   Reinstalling LILO is usually a matter of running /sbin/lilo.
307   You may wish to edit /etc/lilo.conf to specify an entry for your
308   old kernel image (say, /vmlinux.old) in case the new one does not
309   work.  See the LILO docs for more information.
310
311   After reinstalling LILO, you should be all set.  Shutdown the system,
312   reboot, and enjoy!
313
314   If you ever need to change the default root device, video mode,
315   ramdisk size, etc.  in the kernel image, use the 'rdev' program (or
316   alternatively the LILO boot options when appropriate).  No need to
317   recompile the kernel to change these parameters.
318
319 - Reboot with the new kernel and enjoy.
320
321IF SOMETHING GOES WRONG:
322
323 - If you have problems that seem to be due to kernel bugs, please check
324   the file MAINTAINERS to see if there is a particular person associated
325   with the part of the kernel that you are having trouble with. If there
326   isn't anyone listed there, then the second best thing is to mail
327   them to me (torvalds@linux-foundation.org), and possibly to any other
328   relevant mailing-list or to the newsgroup.
329
330 - In all bug-reports, *please* tell what kernel you are talking about,
331   how to duplicate the problem, and what your setup is (use your common
332   sense).  If the problem is new, tell me so, and if the problem is
333   old, please try to tell me when you first noticed it.
334
335 - If the bug results in a message like
336
337     unable to handle kernel paging request at address C0000010
338     Oops: 0002
339     EIP:   0010:XXXXXXXX
340     eax: xxxxxxxx   ebx: xxxxxxxx   ecx: xxxxxxxx   edx: xxxxxxxx
341     esi: xxxxxxxx   edi: xxxxxxxx   ebp: xxxxxxxx
342     ds: xxxx  es: xxxx  fs: xxxx  gs: xxxx
343     Pid: xx, process nr: xx
344     xx xx xx xx xx xx xx xx xx xx
345
346   or similar kernel debugging information on your screen or in your
347   system log, please duplicate it *exactly*.  The dump may look
348   incomprehensible to you, but it does contain information that may
349   help debugging the problem.  The text above the dump is also
350   important: it tells something about why the kernel dumped code (in
351   the above example, it's due to a bad kernel pointer). More information
352   on making sense of the dump is in Documentation/oops-tracing.txt
353
354 - If you compiled the kernel with CONFIG_KALLSYMS you can send the dump
355   as is, otherwise you will have to use the "ksymoops" program to make
356   sense of the dump (but compiling with CONFIG_KALLSYMS is usually preferred).
357   This utility can be downloaded from
358   ftp://ftp.<country>.kernel.org/pub/linux/utils/kernel/ksymoops/ .
359   Alternatively, you can do the dump lookup by hand:
360
361 - In debugging dumps like the above, it helps enormously if you can
362   look up what the EIP value means.  The hex value as such doesn't help
363   me or anybody else very much: it will depend on your particular
364   kernel setup.  What you should do is take the hex value from the EIP
365   line (ignore the "0010:"), and look it up in the kernel namelist to
366   see which kernel function contains the offending address.
367
368   To find out the kernel function name, you'll need to find the system
369   binary associated with the kernel that exhibited the symptom.  This is
370   the file 'linux/vmlinux'.  To extract the namelist and match it against
371   the EIP from the kernel crash, do:
372
373     nm vmlinux | sort | less
374
375   This will give you a list of kernel addresses sorted in ascending
376   order, from which it is simple to find the function that contains the
377   offending address.  Note that the address given by the kernel
378   debugging messages will not necessarily match exactly with the
379   function addresses (in fact, that is very unlikely), so you can't
380   just 'grep' the list: the list will, however, give you the starting
381   point of each kernel function, so by looking for the function that
382   has a starting address lower than the one you are searching for but
383   is followed by a function with a higher address you will find the one
384   you want.  In fact, it may be a good idea to include a bit of
385   "context" in your problem report, giving a few lines around the
386   interesting one.
387
388   If you for some reason cannot do the above (you have a pre-compiled
389   kernel image or similar), telling me as much about your setup as
390   possible will help.  Please read the REPORTING-BUGS document for details.
391
392 - Alternatively, you can use gdb on a running kernel. (read-only; i.e. you
393   cannot change values or set break points.) To do this, first compile the
394   kernel with -g; edit arch/i386/Makefile appropriately, then do a "make
395   clean". You'll also need to enable CONFIG_PROC_FS (via "make config").
396
397   After you've rebooted with the new kernel, do "gdb vmlinux /proc/kcore".
398   You can now use all the usual gdb commands. The command to look up the
399   point where your system crashed is "l *0xXXXXXXXX". (Replace the XXXes
400   with the EIP value.)
401
402   gdb'ing a non-running kernel currently fails because gdb (wrongly)
403   disregards the starting offset for which the kernel is compiled.
404
405