About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Documentation / admin-guide / README.rst




Custom Search

Based on kernel version 4.16.1. Page generated on 2018-04-09 11:52 EST.

1	Linux kernel release 4.x <http://kernel.org/>
2	=============================================
3	
4	These are the release notes for Linux version 4.  Read them carefully,
5	as they tell you what this is all about, explain how to install the
6	kernel, and what to do if something goes wrong.
7	
8	What 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	
23	On 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, AXIS CRIS,
30	  Xtensa, Tilera TILE, ARC and Renesas M32R 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	
40	Documentation
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	
58	Installing 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	
113	Software 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	
125	Build 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	
147	Configuring 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	   You can find more information on using the Linux kernel config tools
222	   in Documentation/kbuild/kconfig.txt.
223	
224	 - NOTES on ``make config``:
225	
226	    - Having unnecessary drivers will make the kernel bigger, and can
227	      under some circumstances lead to problems: probing for a
228	      nonexistent controller card may confuse your other controllers.
229	
230	    - A kernel with math-emulation compiled in will still use the
231	      coprocessor if one is present: the math emulation will just
232	      never get used in that case.  The kernel will be slightly larger,
233	      but will work on different machines regardless of whether they
234	      have a math coprocessor or not.
235	
236	    - The "kernel hacking" configuration details usually result in a
237	      bigger or slower kernel (or both), and can even make the kernel
238	      less stable by configuring some routines to actively try to
239	      break bad code to find kernel problems (kmalloc()).  Thus you
240	      should probably answer 'n' to the questions for "development",
241	      "experimental", or "debugging" features.
242	
243	Compiling the kernel
244	--------------------
245	
246	 - Make sure you have at least gcc 3.2 available.
247	   For more information, refer to :ref:`Documentation/process/changes.rst <changes>`.
248	
249	   Please note that you can still run a.out user programs with this kernel.
250	
251	 - Do a ``make`` to create a compressed kernel image. It is also
252	   possible to do ``make install`` if you have lilo installed to suit the
253	   kernel makefiles, but you may want to check your particular lilo setup first.
254	
255	   To do the actual install, you have to be root, but none of the normal
256	   build should require that. Don't take the name of root in vain.
257	
258	 - If you configured any of the parts of the kernel as ``modules``, you
259	   will also have to do ``make modules_install``.
260	
261	 - Verbose kernel compile/build output:
262	
263	   Normally, the kernel build system runs in a fairly quiet mode (but not
264	   totally silent).  However, sometimes you or other kernel developers need
265	   to see compile, link, or other commands exactly as they are executed.
266	   For this, use "verbose" build mode.  This is done by passing
267	   ``V=1`` to the ``make`` command, e.g.::
268	
269	     make V=1 all
270	
271	   To have the build system also tell the reason for the rebuild of each
272	   target, use ``V=2``.  The default is ``V=0``.
273	
274	 - Keep a backup kernel handy in case something goes wrong.  This is
275	   especially true for the development releases, since each new release
276	   contains new code which has not been debugged.  Make sure you keep a
277	   backup of the modules corresponding to that kernel, as well.  If you
278	   are installing a new kernel with the same version number as your
279	   working kernel, make a backup of your modules directory before you
280	   do a ``make modules_install``.
281	
282	   Alternatively, before compiling, use the kernel config option
283	   "LOCALVERSION" to append a unique suffix to the regular kernel version.
284	   LOCALVERSION can be set in the "General Setup" menu.
285	
286	 - In order to boot your new kernel, you'll need to copy the kernel
287	   image (e.g. .../linux/arch/x86/boot/bzImage after compilation)
288	   to the place where your regular bootable kernel is found.
289	
290	 - Booting a kernel directly from a floppy without the assistance of a
291	   bootloader such as LILO, is no longer supported.
292	
293	   If you boot Linux from the hard drive, chances are you use LILO, which
294	   uses the kernel image as specified in the file /etc/lilo.conf.  The
295	   kernel image file is usually /vmlinuz, /boot/vmlinuz, /bzImage or
296	   /boot/bzImage.  To use the new kernel, save a copy of the old image
297	   and copy the new image over the old one.  Then, you MUST RERUN LILO
298	   to update the loading map! If you don't, you won't be able to boot
299	   the new kernel image.
300	
301	   Reinstalling LILO is usually a matter of running /sbin/lilo.
302	   You may wish to edit /etc/lilo.conf to specify an entry for your
303	   old kernel image (say, /vmlinux.old) in case the new one does not
304	   work.  See the LILO docs for more information.
305	
306	   After reinstalling LILO, you should be all set.  Shutdown the system,
307	   reboot, and enjoy!
308	
309	   If you ever need to change the default root device, video mode,
310	   ramdisk size, etc.  in the kernel image, use the ``rdev`` program (or
311	   alternatively the LILO boot options when appropriate).  No need to
312	   recompile the kernel to change these parameters.
313	
314	 - Reboot with the new kernel and enjoy.
315	
316	If something goes wrong
317	-----------------------
318	
319	 - If you have problems that seem to be due to kernel bugs, please check
320	   the file MAINTAINERS to see if there is a particular person associated
321	   with the part of the kernel that you are having trouble with. If there
322	   isn't anyone listed there, then the second best thing is to mail
323	   them to me (torvalds@linux-foundation.org), and possibly to any other
324	   relevant mailing-list or to the newsgroup.
325	
326	 - In all bug-reports, *please* tell what kernel you are talking about,
327	   how to duplicate the problem, and what your setup is (use your common
328	   sense).  If the problem is new, tell me so, and if the problem is
329	   old, please try to tell me when you first noticed it.
330	
331	 - If the bug results in a message like::
332	
333	     unable to handle kernel paging request at address C0000010
334	     Oops: 0002
335	     EIP:   0010:XXXXXXXX
336	     eax: xxxxxxxx   ebx: xxxxxxxx   ecx: xxxxxxxx   edx: xxxxxxxx
337	     esi: xxxxxxxx   edi: xxxxxxxx   ebp: xxxxxxxx
338	     ds: xxxx  es: xxxx  fs: xxxx  gs: xxxx
339	     Pid: xx, process nr: xx
340	     xx xx xx xx xx xx xx xx xx xx
341	
342	   or similar kernel debugging information on your screen or in your
343	   system log, please duplicate it *exactly*.  The dump may look
344	   incomprehensible to you, but it does contain information that may
345	   help debugging the problem.  The text above the dump is also
346	   important: it tells something about why the kernel dumped code (in
347	   the above example, it's due to a bad kernel pointer). More information
348	   on making sense of the dump is in Documentation/admin-guide/bug-hunting.rst
349	
350	 - If you compiled the kernel with CONFIG_KALLSYMS you can send the dump
351	   as is, otherwise you will have to use the ``ksymoops`` program to make
352	   sense of the dump (but compiling with CONFIG_KALLSYMS is usually preferred).
353	   This utility can be downloaded from
354	   https://www.kernel.org/pub/linux/utils/kernel/ksymoops/ .
355	   Alternatively, you can do the dump lookup by hand:
356	
357	 - In debugging dumps like the above, it helps enormously if you can
358	   look up what the EIP value means.  The hex value as such doesn't help
359	   me or anybody else very much: it will depend on your particular
360	   kernel setup.  What you should do is take the hex value from the EIP
361	   line (ignore the ``0010:``), and look it up in the kernel namelist to
362	   see which kernel function contains the offending address.
363	
364	   To find out the kernel function name, you'll need to find the system
365	   binary associated with the kernel that exhibited the symptom.  This is
366	   the file 'linux/vmlinux'.  To extract the namelist and match it against
367	   the EIP from the kernel crash, do::
368	
369	     nm vmlinux | sort | less
370	
371	   This will give you a list of kernel addresses sorted in ascending
372	   order, from which it is simple to find the function that contains the
373	   offending address.  Note that the address given by the kernel
374	   debugging messages will not necessarily match exactly with the
375	   function addresses (in fact, that is very unlikely), so you can't
376	   just 'grep' the list: the list will, however, give you the starting
377	   point of each kernel function, so by looking for the function that
378	   has a starting address lower than the one you are searching for but
379	   is followed by a function with a higher address you will find the one
380	   you want.  In fact, it may be a good idea to include a bit of
381	   "context" in your problem report, giving a few lines around the
382	   interesting one.
383	
384	   If you for some reason cannot do the above (you have a pre-compiled
385	   kernel image or similar), telling me as much about your setup as
386	   possible will help.  Please read the :ref:`admin-guide/reporting-bugs.rst <reportingbugs>`
387	   document for details.
388	
389	 - Alternatively, you can use gdb on a running kernel. (read-only; i.e. you
390	   cannot change values or set break points.) To do this, first compile the
391	   kernel with -g; edit arch/x86/Makefile appropriately, then do a ``make
392	   clean``. You'll also need to enable CONFIG_PROC_FS (via ``make config``).
393	
394	   After you've rebooted with the new kernel, do ``gdb vmlinux /proc/kcore``.
395	   You can now use all the usual gdb commands. The command to look up the
396	   point where your system crashed is ``l *0xXXXXXXXX``. (Replace the XXXes
397	   with the EIP value.)
398	
399	   gdb'ing a non-running kernel currently fails because ``gdb`` (wrongly)
400	   disregards the starting offset for which the kernel is compiled.
Hide Line Numbers
About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Information is copyright its respective author. All material is available from the Linux Kernel Source distributed under a GPL License. This page is provided as a free service by mjmwired.net.