3 Linux kernel release 4.x <http://kernel.org/>
4 =============================================
6 These are the release notes for Linux version 4. 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.
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.
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.
22 It is distributed under the GNU General Public License v2 - see the
23 accompanying COPYING file for more details.
25 On what hardware does it run?
26 -----------------------------
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
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).
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.
52 - There are various README files in the Documentation/ subdirectory:
53 these typically contain kernel-specific installation notes for some
54 drivers for example. See Documentation/00-INDEX for a list of what
55 is contained in each file. Please read the
56 :ref:`Documentation/process/changes.rst <changes>` file, as it
57 contains information about the problems, which may result by upgrading
60 Installing the kernel source
61 ----------------------------
63 - If you install the full sources, put the kernel tarball in a
64 directory where you have permissions (e.g. your home directory) and
67 xz -cd linux-4.X.tar.xz | tar xvf -
69 Replace "X" with the version number of the latest kernel.
71 Do NOT use the /usr/src/linux area! This area has a (usually
72 incomplete) set of kernel headers that are used by the library header
73 files. They should match the library, and not get messed up by
74 whatever the kernel-du-jour happens to be.
76 - You can also upgrade between 4.x releases by patching. Patches are
77 distributed in the xz format. To install by patching, get all the
78 newer patch files, enter the top level directory of the kernel source
79 (linux-4.X) and execute::
81 xz -cd ../patch-4.x.xz | patch -p1
83 Replace "x" for all versions bigger than the version "X" of your current
84 source tree, **in_order**, and you should be ok. You may want to remove
85 the backup files (some-file-name~ or some-file-name.orig), and make sure
86 that there are no failed patches (some-file-name# or some-file-name.rej).
87 If there are, either you or I have made a mistake.
89 Unlike patches for the 4.x kernels, patches for the 4.x.y kernels
90 (also known as the -stable kernels) are not incremental but instead apply
91 directly to the base 4.x kernel. For example, if your base kernel is 4.0
92 and you want to apply the 4.0.3 patch, you must not first apply the 4.0.1
93 and 4.0.2 patches. Similarly, if you are running kernel version 4.0.2 and
94 want to jump to 4.0.3, you must first reverse the 4.0.2 patch (that is,
95 patch -R) **before** applying the 4.0.3 patch. You can read more on this in
96 :ref:`Documentation/process/applying-patches.rst <applying_patches>`.
98 Alternatively, the script patch-kernel can be used to automate this
99 process. It determines the current kernel version and applies any
102 linux/scripts/patch-kernel linux
104 The first argument in the command above is the location of the
105 kernel source. Patches are applied from the current directory, but
106 an alternative directory can be specified as the second argument.
108 - Make sure you have no stale .o files and dependencies lying around::
113 You should now have the sources correctly installed.
115 Software requirements
116 ---------------------
118 Compiling and running the 4.x kernels requires up-to-date
119 versions of various software packages. Consult
120 :ref:`Documentation/process/changes.rst <changes>` for the minimum version numbers
121 required and how to get updates for these packages. Beware that using
122 excessively old versions of these packages can cause indirect
123 errors that are very difficult to track down, so don't assume that
124 you can just update packages when obvious problems arise during
127 Build directory for the kernel
128 ------------------------------
130 When compiling the kernel, all output files will per default be
131 stored together with the kernel source code.
132 Using the option ``make O=output/dir`` allows you to specify an alternate
133 place for the output files (including .config).
136 kernel source code: /usr/src/linux-4.X
137 build directory: /home/name/build/kernel
139 To configure and build the kernel, use::
141 cd /usr/src/linux-4.X
142 make O=/home/name/build/kernel menuconfig
143 make O=/home/name/build/kernel
144 sudo make O=/home/name/build/kernel modules_install install
146 Please note: If the ``O=output/dir`` option is used, then it must be
147 used for all invocations of make.
149 Configuring the kernel
150 ----------------------
152 Do not skip this step even if you are only upgrading one minor
153 version. New configuration options are added in each release, and
154 odd problems will turn up if the configuration files are not set up
155 as expected. If you want to carry your existing configuration to a
156 new version with minimal work, use ``make oldconfig``, which will
157 only ask you for the answers to new questions.
159 - Alternative configuration commands are::
161 "make config" Plain text interface.
163 "make menuconfig" Text based color menus, radiolists & dialogs.
165 "make nconfig" Enhanced text based color menus.
167 "make xconfig" Qt based configuration tool.
169 "make gconfig" GTK+ based configuration tool.
171 "make oldconfig" Default all questions based on the contents of
172 your existing ./.config file and asking about
176 Like above, but sets new symbols to their default
177 values without prompting.
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.
184 "make ${PLATFORM}_defconfig"
185 Create a ./.config file by using the default
187 arch/$ARCH/configs/${PLATFORM}_defconfig.
188 Use "make help" to get a list of all available
189 platforms of your architecture.
192 Create a ./.config file by setting symbol
193 values to 'y' as much as possible.
196 Create a ./.config file by setting symbol
197 values to 'm' as much as possible.
199 "make allnoconfig" Create a ./.config file by setting symbol
200 values to 'n' as much as possible.
202 "make randconfig" Create a ./.config file by setting symbol
203 values to random values.
205 "make localmodconfig" Create a config based on current config and
206 loaded modules (lsmod). Disables any module
207 option that is not needed for the loaded modules.
209 To create a localmodconfig for another machine,
210 store the lsmod of that machine into a file
211 and pass it in as a LSMOD parameter.
213 target$ lsmod > /tmp/mylsmod
214 target$ scp /tmp/mylsmod host:/tmp
216 host$ make LSMOD=/tmp/mylsmod localmodconfig
218 The above also works when cross compiling.
220 "make localyesconfig" Similar to localmodconfig, except it will convert
221 all module options to built in (=y) options.
223 "make kvmconfig" Enable additional options for kvm guest kernel support.
225 "make xenconfig" Enable additional options for xen dom0 guest kernel
228 "make tinyconfig" Configure the tiniest possible kernel.
230 You can find more information on using the Linux kernel config tools
231 in Documentation/kbuild/kconfig.txt.
233 - NOTES on ``make config``:
235 - Having unnecessary drivers will make the kernel bigger, and can
236 under some circumstances lead to problems: probing for a
237 nonexistent controller card may confuse your other controllers.
239 - A kernel with math-emulation compiled in will still use the
240 coprocessor if one is present: the math emulation will just
241 never get used in that case. The kernel will be slightly larger,
242 but will work on different machines regardless of whether they
243 have a math coprocessor or not.
245 - The "kernel hacking" configuration details usually result in a
246 bigger or slower kernel (or both), and can even make the kernel
247 less stable by configuring some routines to actively try to
248 break bad code to find kernel problems (kmalloc()). Thus you
249 should probably answer 'n' to the questions for "development",
250 "experimental", or "debugging" features.
255 - Make sure you have at least gcc 3.2 available.
256 For more information, refer to :ref:`Documentation/process/changes.rst <changes>`.
258 Please note that you can still run a.out user programs with this kernel.
260 - Do a ``make`` to create a compressed kernel image. It is also
261 possible to do ``make install`` if you have lilo installed to suit the
262 kernel makefiles, but you may want to check your particular lilo setup first.
264 To do the actual install, you have to be root, but none of the normal
265 build should require that. Don't take the name of root in vain.
267 - If you configured any of the parts of the kernel as ``modules``, you
268 will also have to do ``make modules_install``.
270 - Verbose kernel compile/build output:
272 Normally, the kernel build system runs in a fairly quiet mode (but not
273 totally silent). However, sometimes you or other kernel developers need
274 to see compile, link, or other commands exactly as they are executed.
275 For this, use "verbose" build mode. This is done by passing
276 ``V=1`` to the ``make`` command, e.g.::
280 To have the build system also tell the reason for the rebuild of each
281 target, use ``V=2``. The default is ``V=0``.
283 - Keep a backup kernel handy in case something goes wrong. This is
284 especially true for the development releases, since each new release
285 contains new code which has not been debugged. Make sure you keep a
286 backup of the modules corresponding to that kernel, as well. If you
287 are installing a new kernel with the same version number as your
288 working kernel, make a backup of your modules directory before you
289 do a ``make modules_install``.
291 Alternatively, before compiling, use the kernel config option
292 "LOCALVERSION" to append a unique suffix to the regular kernel version.
293 LOCALVERSION can be set in the "General Setup" menu.
295 - In order to boot your new kernel, you'll need to copy the kernel
296 image (e.g. .../linux/arch/x86/boot/bzImage after compilation)
297 to the place where your regular bootable kernel is found.
299 - Booting a kernel directly from a floppy without the assistance of a
300 bootloader such as LILO, is no longer supported.
302 If you boot Linux from the hard drive, chances are you use LILO, which
303 uses the kernel image as specified in the file /etc/lilo.conf. The
304 kernel image file is usually /vmlinuz, /boot/vmlinuz, /bzImage or
305 /boot/bzImage. To use the new kernel, save a copy of the old image
306 and copy the new image over the old one. Then, you MUST RERUN LILO
307 to update the loading map! If you don't, you won't be able to boot
308 the new kernel image.
310 Reinstalling LILO is usually a matter of running /sbin/lilo.
311 You may wish to edit /etc/lilo.conf to specify an entry for your
312 old kernel image (say, /vmlinux.old) in case the new one does not
313 work. See the LILO docs for more information.
315 After reinstalling LILO, you should be all set. Shutdown the system,
318 If you ever need to change the default root device, video mode,
319 ramdisk size, etc. in the kernel image, use the ``rdev`` program (or
320 alternatively the LILO boot options when appropriate). No need to
321 recompile the kernel to change these parameters.
323 - Reboot with the new kernel and enjoy.
325 If something goes wrong
326 -----------------------
328 - If you have problems that seem to be due to kernel bugs, please check
329 the file MAINTAINERS to see if there is a particular person associated
330 with the part of the kernel that you are having trouble with. If there
331 isn't anyone listed there, then the second best thing is to mail
332 them to me (torvalds@linux-foundation.org), and possibly to any other
333 relevant mailing-list or to the newsgroup.
335 - In all bug-reports, *please* tell what kernel you are talking about,
336 how to duplicate the problem, and what your setup is (use your common
337 sense). If the problem is new, tell me so, and if the problem is
338 old, please try to tell me when you first noticed it.
340 - If the bug results in a message like::
342 unable to handle kernel paging request at address C0000010
345 eax: xxxxxxxx ebx: xxxxxxxx ecx: xxxxxxxx edx: xxxxxxxx
346 esi: xxxxxxxx edi: xxxxxxxx ebp: xxxxxxxx
347 ds: xxxx es: xxxx fs: xxxx gs: xxxx
348 Pid: xx, process nr: xx
349 xx xx xx xx xx xx xx xx xx xx
351 or similar kernel debugging information on your screen or in your
352 system log, please duplicate it *exactly*. The dump may look
353 incomprehensible to you, but it does contain information that may
354 help debugging the problem. The text above the dump is also
355 important: it tells something about why the kernel dumped code (in
356 the above example, it's due to a bad kernel pointer). More information
357 on making sense of the dump is in Documentation/admin-guide/bug-hunting.rst
359 - If you compiled the kernel with CONFIG_KALLSYMS you can send the dump
360 as is, otherwise you will have to use the ``ksymoops`` program to make
361 sense of the dump (but compiling with CONFIG_KALLSYMS is usually preferred).
362 This utility can be downloaded from
363 https://www.kernel.org/pub/linux/utils/kernel/ksymoops/ .
364 Alternatively, you can do the dump lookup by hand:
366 - In debugging dumps like the above, it helps enormously if you can
367 look up what the EIP value means. The hex value as such doesn't help
368 me or anybody else very much: it will depend on your particular
369 kernel setup. What you should do is take the hex value from the EIP
370 line (ignore the ``0010:``), and look it up in the kernel namelist to
371 see which kernel function contains the offending address.
373 To find out the kernel function name, you'll need to find the system
374 binary associated with the kernel that exhibited the symptom. This is
375 the file 'linux/vmlinux'. To extract the namelist and match it against
376 the EIP from the kernel crash, do::
378 nm vmlinux | sort | less
380 This will give you a list of kernel addresses sorted in ascending
381 order, from which it is simple to find the function that contains the
382 offending address. Note that the address given by the kernel
383 debugging messages will not necessarily match exactly with the
384 function addresses (in fact, that is very unlikely), so you can't
385 just 'grep' the list: the list will, however, give you the starting
386 point of each kernel function, so by looking for the function that
387 has a starting address lower than the one you are searching for but
388 is followed by a function with a higher address you will find the one
389 you want. In fact, it may be a good idea to include a bit of
390 "context" in your problem report, giving a few lines around the
393 If you for some reason cannot do the above (you have a pre-compiled
394 kernel image or similar), telling me as much about your setup as
395 possible will help. Please read the :ref:`admin-guide/reporting-bugs.rst <reportingbugs>`
396 document for details.
398 - Alternatively, you can use gdb on a running kernel. (read-only; i.e. you
399 cannot change values or set break points.) To do this, first compile the
400 kernel with -g; edit arch/x86/Makefile appropriately, then do a ``make
401 clean``. You'll also need to enable CONFIG_PROC_FS (via ``make config``).
403 After you've rebooted with the new kernel, do ``gdb vmlinux /proc/kcore``.
404 You can now use all the usual gdb commands. The command to look up the
405 point where your system crashed is ``l *0xXXXXXXXX``. (Replace the XXXes
408 gdb'ing a non-running kernel currently fails because ``gdb`` (wrongly)
409 disregards the starting offset for which the kernel is compiled.
git.samba.org / sfrench / cifs-2.6.git / blob