1 .. _readme: !! 1 Linux kernel release 4.x <http://kernel.org/>
2 <<
3 Linux kernel release 6.x <http://kernel.org/> <<
4 ============================================= 2 =============================================
5 3
6 These are the release notes for Linux version !! 4 These are the release notes for Linux version 4. Read them carefully,
7 as they tell you what this is all about, expla 5 as they tell you what this is all about, explain how to install the
8 kernel, and what to do if something goes wrong 6 kernel, and what to do if something goes wrong.
9 7
10 What is Linux? 8 What is Linux?
11 -------------- 9 --------------
12 10
13 Linux is a clone of the operating system Uni 11 Linux is a clone of the operating system Unix, written from scratch by
14 Linus Torvalds with assistance from a loosel 12 Linus Torvalds with assistance from a loosely-knit team of hackers across
15 the Net. It aims towards POSIX and Single UN 13 the Net. It aims towards POSIX and Single UNIX Specification compliance.
16 14
17 It has all the features you would expect in 15 It has all the features you would expect in a modern fully-fledged Unix,
18 including true multitasking, virtual memory, 16 including true multitasking, virtual memory, shared libraries, demand
19 loading, shared copy-on-write executables, p 17 loading, shared copy-on-write executables, proper memory management,
20 and multistack networking including IPv4 and 18 and multistack networking including IPv4 and IPv6.
21 19
22 It is distributed under the GNU General Publ 20 It is distributed under the GNU General Public License v2 - see the
23 accompanying COPYING file for more details. 21 accompanying COPYING file for more details.
24 22
25 On what hardware does it run? 23 On what hardware does it run?
26 ----------------------------- 24 -----------------------------
27 25
28 Although originally developed first for 32-b 26 Although originally developed first for 32-bit x86-based PCs (386 or higher),
29 today Linux also runs on (at least) the Comp 27 today Linux also runs on (at least) the Compaq Alpha AXP, Sun SPARC and
30 UltraSPARC, Motorola 68000, PowerPC, PowerPC 28 UltraSPARC, Motorola 68000, PowerPC, PowerPC64, ARM, Hitachi SuperH, Cell,
31 IBM S/390, MIPS, HP PA-RISC, Intel IA-64, DE !! 29 IBM S/390, MIPS, HP PA-RISC, Intel IA-64, DEC VAX, AMD x86-64, AXIS CRIS,
32 ARC architectures. !! 30 Xtensa, Tilera TILE, AVR32, ARC and Renesas M32R architectures.
33 31
34 Linux is easily portable to most general-pur 32 Linux is easily portable to most general-purpose 32- or 64-bit architectures
35 as long as they have a paged memory manageme 33 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 Compil 34 GNU C compiler (gcc) (part of The GNU Compiler Collection, GCC). Linux has
37 also been ported to a number of architecture 35 also been ported to a number of architectures without a PMMU, although
38 functionality is then obviously somewhat lim 36 functionality is then obviously somewhat limited.
39 Linux has also been ported to itself. You ca 37 Linux has also been ported to itself. You can now run the kernel as a
40 userspace application - this is called UserM 38 userspace application - this is called UserMode Linux (UML).
41 39
42 Documentation 40 Documentation
43 ------------- 41 -------------
44 42
45 - There is a lot of documentation available b 43 - There is a lot of documentation available both in electronic form on
46 the Internet and in books, both Linux-speci 44 the Internet and in books, both Linux-specific and pertaining to
47 general UNIX questions. I'd recommend look 45 general UNIX questions. I'd recommend looking into the documentation
48 subdirectories on any Linux FTP site for th 46 subdirectories on any Linux FTP site for the LDP (Linux Documentation
49 Project) books. This README is not meant t 47 Project) books. This README is not meant to be documentation on the
50 system: there are much better sources avail 48 system: there are much better sources available.
51 49
52 - There are various README files in the Docum 50 - There are various README files in the Documentation/ subdirectory:
53 these typically contain kernel-specific ins 51 these typically contain kernel-specific installation notes for some
54 drivers for example. Please read the !! 52 drivers for example. See Documentation/00-INDEX for a list of what
>> 53 is contained in each file. Please read the
55 :ref:`Documentation/process/changes.rst <ch 54 :ref:`Documentation/process/changes.rst <changes>` file, as it
56 contains information about the problems, wh 55 contains information about the problems, which may result by upgrading
57 your kernel. 56 your kernel.
58 57
>> 58 - The Documentation/DocBook/ subdirectory contains several guides for
>> 59 kernel developers and users. These guides can be rendered in a
>> 60 number of formats: PostScript (.ps), PDF, HTML, & man-pages, among others.
>> 61 After installation, ``make psdocs``, ``make pdfdocs``, ``make htmldocs``,
>> 62 or ``make mandocs`` will render the documentation in the requested format.
>> 63
59 Installing the kernel source 64 Installing the kernel source
60 ---------------------------- 65 ----------------------------
61 66
62 - If you install the full sources, put the ke 67 - If you install the full sources, put the kernel tarball in a
63 directory where you have permissions (e.g. 68 directory where you have permissions (e.g. your home directory) and
64 unpack it:: 69 unpack it::
65 70
66 xz -cd linux-6.x.tar.xz | tar xvf - !! 71 xz -cd linux-4.X.tar.xz | tar xvf -
67 72
68 Replace "X" with the version number of the 73 Replace "X" with the version number of the latest kernel.
69 74
70 Do NOT use the /usr/src/linux area! This ar 75 Do NOT use the /usr/src/linux area! This area has a (usually
71 incomplete) set of kernel headers that are 76 incomplete) set of kernel headers that are used by the library header
72 files. They should match the library, and 77 files. They should match the library, and not get messed up by
73 whatever the kernel-du-jour happens to be. 78 whatever the kernel-du-jour happens to be.
74 79
75 - You can also upgrade between 6.x releases b !! 80 - You can also upgrade between 4.x releases by patching. Patches are
76 distributed in the xz format. To install b 81 distributed in the xz format. To install by patching, get all the
77 newer patch files, enter the top level dire 82 newer patch files, enter the top level directory of the kernel source
78 (linux-6.x) and execute:: !! 83 (linux-4.X) and execute::
79 84
80 xz -cd ../patch-6.x.xz | patch -p1 !! 85 xz -cd ../patch-4.x.xz | patch -p1
81 86
82 Replace "x" for all versions bigger than th !! 87 Replace "x" for all versions bigger than the version "X" of your current
83 source tree, **in_order**, and you should b 88 source tree, **in_order**, and you should be ok. You may want to remove
84 the backup files (some-file-name~ or some-f 89 the backup files (some-file-name~ or some-file-name.orig), and make sure
85 that there are no failed patches (some-file 90 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 m 91 If there are, either you or I have made a mistake.
87 92
88 Unlike patches for the 6.x kernels, patches !! 93 Unlike patches for the 4.x kernels, patches for the 4.x.y kernels
89 (also known as the -stable kernels) are not 94 (also known as the -stable kernels) are not incremental but instead apply
90 directly to the base 6.x kernel. For examp !! 95 directly to the base 4.x kernel. For example, if your base kernel is 4.0
91 and you want to apply the 6.0.3 patch, you !! 96 and you want to apply the 4.0.3 patch, you must not first apply the 4.0.1
92 and 6.0.2 patches. Similarly, if you are ru !! 97 and 4.0.2 patches. Similarly, if you are running kernel version 4.0.2 and
93 want to jump to 6.0.3, you must first rever !! 98 want to jump to 4.0.3, you must first reverse the 4.0.2 patch (that is,
94 patch -R) **before** applying the 6.0.3 pat !! 99 patch -R) **before** applying the 4.0.3 patch. You can read more on this in
95 :ref:`Documentation/process/applying-patche 100 :ref:`Documentation/process/applying-patches.rst <applying_patches>`.
96 101
97 Alternatively, the script patch-kernel can 102 Alternatively, the script patch-kernel can be used to automate this
98 process. It determines the current kernel 103 process. It determines the current kernel version and applies any
99 patches found:: 104 patches found::
100 105
101 linux/scripts/patch-kernel linux 106 linux/scripts/patch-kernel linux
102 107
103 The first argument in the command above is 108 The first argument in the command above is the location of the
104 kernel source. Patches are applied from th 109 kernel source. Patches are applied from the current directory, but
105 an alternative directory can be specified a 110 an alternative directory can be specified as the second argument.
106 111
107 - Make sure you have no stale .o files and de 112 - Make sure you have no stale .o files and dependencies lying around::
108 113
109 cd linux 114 cd linux
110 make mrproper 115 make mrproper
111 116
112 You should now have the sources correctly i 117 You should now have the sources correctly installed.
113 118
114 Software requirements 119 Software requirements
115 --------------------- 120 ---------------------
116 121
117 Compiling and running the 6.x kernels requi !! 122 Compiling and running the 4.x kernels requires up-to-date
118 versions of various software packages. Con 123 versions of various software packages. Consult
119 :ref:`Documentation/process/changes.rst <ch 124 :ref:`Documentation/process/changes.rst <changes>` for the minimum version numbers
120 required and how to get updates for these p 125 required and how to get updates for these packages. Beware that using
121 excessively old versions of these packages 126 excessively old versions of these packages can cause indirect
122 errors that are very difficult to track dow 127 errors that are very difficult to track down, so don't assume that
123 you can just update packages when obvious p 128 you can just update packages when obvious problems arise during
124 build or operation. 129 build or operation.
125 130
126 Build directory for the kernel 131 Build directory for the kernel
127 ------------------------------ 132 ------------------------------
128 133
129 When compiling the kernel, all output files 134 When compiling the kernel, all output files will per default be
130 stored together with the kernel source code 135 stored together with the kernel source code.
131 Using the option ``make O=output/dir`` allo 136 Using the option ``make O=output/dir`` allows you to specify an alternate
132 place for the output files (including .conf 137 place for the output files (including .config).
133 Example:: 138 Example::
134 139
135 kernel source code: /usr/src/linux-6.x !! 140 kernel source code: /usr/src/linux-4.X
136 build directory: /home/name/build/kern 141 build directory: /home/name/build/kernel
137 142
138 To configure and build the kernel, use:: 143 To configure and build the kernel, use::
139 144
140 cd /usr/src/linux-6.x !! 145 cd /usr/src/linux-4.X
141 make O=/home/name/build/kernel menuconfig 146 make O=/home/name/build/kernel menuconfig
142 make O=/home/name/build/kernel 147 make O=/home/name/build/kernel
143 sudo make O=/home/name/build/kernel modul 148 sudo make O=/home/name/build/kernel modules_install install
144 149
145 Please note: If the ``O=output/dir`` option 150 Please note: If the ``O=output/dir`` option is used, then it must be
146 used for all invocations of make. 151 used for all invocations of make.
147 152
148 Configuring the kernel 153 Configuring the kernel
149 ---------------------- 154 ----------------------
150 155
151 Do not skip this step even if you are only 156 Do not skip this step even if you are only upgrading one minor
152 version. New configuration options are add 157 version. New configuration options are added in each release, and
153 odd problems will turn up if the configurat 158 odd problems will turn up if the configuration files are not set up
154 as expected. If you want to carry your exi 159 as expected. If you want to carry your existing configuration to a
155 new version with minimal work, use ``make o 160 new version with minimal work, use ``make oldconfig``, which will
156 only ask you for the answers to new questio 161 only ask you for the answers to new questions.
157 162
158 - Alternative configuration commands are:: 163 - Alternative configuration commands are::
159 164
160 "make config" Plain text interface. 165 "make config" Plain text interface.
161 166
162 "make menuconfig" Text based color menus 167 "make menuconfig" Text based color menus, radiolists & dialogs.
163 168
164 "make nconfig" Enhanced text based co 169 "make nconfig" Enhanced text based color menus.
165 170
166 "make xconfig" Qt based configuration 171 "make xconfig" Qt based configuration tool.
167 172
168 "make gconfig" GTK+ based configurati 173 "make gconfig" GTK+ based configuration tool.
169 174
170 "make oldconfig" Default all questions 175 "make oldconfig" Default all questions based on the contents of
171 your existing ./.confi 176 your existing ./.config file and asking about
172 new config symbols. 177 new config symbols.
173 178
>> 179 "make silentoldconfig"
>> 180 Like above, but avoids cluttering the screen
>> 181 with questions already answered.
>> 182 Additionally updates the dependencies.
>> 183
174 "make olddefconfig" 184 "make olddefconfig"
175 Like above, but sets n 185 Like above, but sets new symbols to their default
176 values without prompti 186 values without prompting.
177 187
178 "make defconfig" Create a ./.config fil 188 "make defconfig" Create a ./.config file by using the default
179 symbol values from eit 189 symbol values from either arch/$ARCH/defconfig
180 or arch/$ARCH/configs/ 190 or arch/$ARCH/configs/${PLATFORM}_defconfig,
181 depending on the archi 191 depending on the architecture.
182 192
183 "make ${PLATFORM}_defconfig" 193 "make ${PLATFORM}_defconfig"
184 Create a ./.config fil 194 Create a ./.config file by using the default
185 symbol values from 195 symbol values from
186 arch/$ARCH/configs/${P 196 arch/$ARCH/configs/${PLATFORM}_defconfig.
187 Use "make help" to get 197 Use "make help" to get a list of all available
188 platforms of your arch 198 platforms of your architecture.
189 199
190 "make allyesconfig" 200 "make allyesconfig"
191 Create a ./.config fil 201 Create a ./.config file by setting symbol
192 values to 'y' as much 202 values to 'y' as much as possible.
193 203
194 "make allmodconfig" 204 "make allmodconfig"
195 Create a ./.config fil 205 Create a ./.config file by setting symbol
196 values to 'm' as much 206 values to 'm' as much as possible.
197 207
198 "make allnoconfig" Create a ./.config fil 208 "make allnoconfig" Create a ./.config file by setting symbol
199 values to 'n' as much 209 values to 'n' as much as possible.
200 210
201 "make randconfig" Create a ./.config fil 211 "make randconfig" Create a ./.config file by setting symbol
202 values to random value 212 values to random values.
203 213
204 "make localmodconfig" Create a config bas 214 "make localmodconfig" Create a config based on current config and
205 loaded modules (lsm 215 loaded modules (lsmod). Disables any module
206 option that is not 216 option that is not needed for the loaded modules.
207 217
208 To create a localmo 218 To create a localmodconfig for another machine,
209 store the lsmod of 219 store the lsmod of that machine into a file
210 and pass it in as a 220 and pass it in as a LSMOD parameter.
211 221
212 Also, you can prese <<
213 or kconfig files by <<
214 parameter LMC_KEEP. <<
215 <<
216 target$ lsmod > /tmp/mylsmo 222 target$ lsmod > /tmp/mylsmod
217 target$ scp /tmp/mylsmod ho 223 target$ scp /tmp/mylsmod host:/tmp
218 224
219 host$ make LSMOD=/tmp/mylsm !! 225 host$ make LSMOD=/tmp/mylsmod localmodconfig
220 LMC_KEEP="drivers/u <<
221 localmodconfig <<
222 226
223 The above also work 227 The above also works when cross compiling.
224 228
225 "make localyesconfig" Similar to localmod 229 "make localyesconfig" Similar to localmodconfig, except it will convert
226 all module options !! 230 all module options to built in (=y) options.
227 also preserve modul <<
228 <<
229 "make kvm_guest.config" Enable addition <<
230 support. <<
231 <<
232 "make xen.config" Enable additional opt <<
233 support. <<
234 <<
235 "make tinyconfig" Configure the tiniest <<
236 231
237 You can find more information on using the 232 You can find more information on using the Linux kernel config tools
238 in Documentation/kbuild/kconfig.rst. !! 233 in Documentation/kbuild/kconfig.txt.
239 234
240 - NOTES on ``make config``: 235 - NOTES on ``make config``:
241 236
242 - Having unnecessary drivers will make the 237 - Having unnecessary drivers will make the kernel bigger, and can
243 under some circumstances lead to problem 238 under some circumstances lead to problems: probing for a
244 nonexistent controller card may confuse 239 nonexistent controller card may confuse your other controllers.
245 240
246 - A kernel with math-emulation compiled in 241 - A kernel with math-emulation compiled in will still use the
247 coprocessor if one is present: the math 242 coprocessor if one is present: the math emulation will just
248 never get used in that case. The kernel 243 never get used in that case. The kernel will be slightly larger,
249 but will work on different machines rega 244 but will work on different machines regardless of whether they
250 have a math coprocessor or not. 245 have a math coprocessor or not.
251 246
252 - The "kernel hacking" configuration detai 247 - The "kernel hacking" configuration details usually result in a
253 bigger or slower kernel (or both), and c 248 bigger or slower kernel (or both), and can even make the kernel
254 less stable by configuring some routines 249 less stable by configuring some routines to actively try to
255 break bad code to find kernel problems ( 250 break bad code to find kernel problems (kmalloc()). Thus you
256 should probably answer 'n' to the questi 251 should probably answer 'n' to the questions for "development",
257 "experimental", or "debugging" features. 252 "experimental", or "debugging" features.
258 253
259 Compiling the kernel 254 Compiling the kernel
260 -------------------- 255 --------------------
261 256
262 - Make sure you have at least gcc 5.1 availab !! 257 - Make sure you have at least gcc 3.2 available.
263 For more information, refer to :ref:`Docume 258 For more information, refer to :ref:`Documentation/process/changes.rst <changes>`.
264 259
265 - Do a ``make`` to create a compressed kernel !! 260 Please note that you can still run a.out user programs with this kernel.
266 ``make install`` if you have lilo installed !! 261
267 install script recognised by the kernel's i !! 262 - Do a ``make`` to create a compressed kernel image. It is also
268 distributions will have a recognized instal !! 263 possible to do ``make install`` if you have lilo installed to suit the
269 check your distribution's setup first. !! 264 kernel makefiles, but you may want to check your particular lilo setup first.
270 265
271 To do the actual install, you have to be ro 266 To do the actual install, you have to be root, but none of the normal
272 build should require that. Don't take the n 267 build should require that. Don't take the name of root in vain.
273 268
274 - If you configured any of the parts of the k 269 - If you configured any of the parts of the kernel as ``modules``, you
275 will also have to do ``make modules_install 270 will also have to do ``make modules_install``.
276 271
277 - Verbose kernel compile/build output: 272 - Verbose kernel compile/build output:
278 273
279 Normally, the kernel build system runs in a 274 Normally, the kernel build system runs in a fairly quiet mode (but not
280 totally silent). However, sometimes you or 275 totally silent). However, sometimes you or other kernel developers need
281 to see compile, link, or other commands exa 276 to see compile, link, or other commands exactly as they are executed.
282 For this, use "verbose" build mode. This i 277 For this, use "verbose" build mode. This is done by passing
283 ``V=1`` to the ``make`` command, e.g.:: 278 ``V=1`` to the ``make`` command, e.g.::
284 279
285 make V=1 all 280 make V=1 all
286 281
287 To have the build system also tell the reas 282 To have the build system also tell the reason for the rebuild of each
288 target, use ``V=2``. The default is ``V=0` 283 target, use ``V=2``. The default is ``V=0``.
289 284
290 - Keep a backup kernel handy in case somethin 285 - Keep a backup kernel handy in case something goes wrong. This is
291 especially true for the development release 286 especially true for the development releases, since each new release
292 contains new code which has not been debugg 287 contains new code which has not been debugged. Make sure you keep a
293 backup of the modules corresponding to that 288 backup of the modules corresponding to that kernel, as well. If you
294 are installing a new kernel with the same v 289 are installing a new kernel with the same version number as your
295 working kernel, make a backup of your modul 290 working kernel, make a backup of your modules directory before you
296 do a ``make modules_install``. 291 do a ``make modules_install``.
297 292
298 Alternatively, before compiling, use the ke 293 Alternatively, before compiling, use the kernel config option
299 "LOCALVERSION" to append a unique suffix to 294 "LOCALVERSION" to append a unique suffix to the regular kernel version.
300 LOCALVERSION can be set in the "General Set 295 LOCALVERSION can be set in the "General Setup" menu.
301 296
302 - In order to boot your new kernel, you'll ne 297 - In order to boot your new kernel, you'll need to copy the kernel
303 image (e.g. .../linux/arch/x86/boot/bzImage 298 image (e.g. .../linux/arch/x86/boot/bzImage after compilation)
304 to the place where your regular bootable ke 299 to the place where your regular bootable kernel is found.
305 300
306 - Booting a kernel directly from a storage de !! 301 - Booting a kernel directly from a floppy without the assistance of a
307 of a bootloader such as LILO or GRUB, is no !! 302 bootloader such as LILO, is no longer supported.
308 (non-EFI systems). On UEFI/EFI systems, how <<
309 which allows the motherboard to boot direct <<
310 On modern workstations and desktops, it's g <<
311 bootloader as difficulties can arise with m <<
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 <<
316 active development, though as it was extrem <<
317 in documentation. Popular alternatives incl <<
318 systemd-boot, or EFISTUB. For various reaso <<
319 software that's no longer in active develop <<
320 <<
321 - Chances are your distribution includes an i <<
322 ``make install`` will be all that's needed. <<
323 you'll have to identify your bootloader and <<
324 configure your EFI. <<
325 <<
326 Legacy LILO Instructions <<
327 ------------------------ <<
328 <<
329 <<
330 - If you use LILO the kernel images are speci <<
331 The kernel image file is usually /vmlinuz, <<
332 /boot/bzImage. To use the new kernel, save <<
333 the new image over the old one. Then, you M <<
334 loading map! If you don't, you won't be abl <<
335 <<
336 - Reinstalling LILO is usually a matter of ru <<
337 to edit /etc/lilo.conf to specify an entry <<
338 (say, /vmlinux.old) in case the new one doe <<
339 for more information. <<
340 303
341 - After reinstalling LILO, you should be all !! 304 If you boot Linux from the hard drive, chances are you use LILO, which
>> 305 uses the kernel image as specified in the file /etc/lilo.conf. The
>> 306 kernel image file is usually /vmlinuz, /boot/vmlinuz, /bzImage or
>> 307 /boot/bzImage. To use the new kernel, save a copy of the old image
>> 308 and copy the new image over the old one. Then, you MUST RERUN LILO
>> 309 to update the loading map! If you don't, you won't be able to boot
>> 310 the new kernel image.
>> 311
>> 312 Reinstalling LILO is usually a matter of running /sbin/lilo.
>> 313 You may wish to edit /etc/lilo.conf to specify an entry for your
>> 314 old kernel image (say, /vmlinux.old) in case the new one does not
>> 315 work. See the LILO docs for more information.
>> 316
>> 317 After reinstalling LILO, you should be all set. Shutdown the system,
342 reboot, and enjoy! 318 reboot, and enjoy!
343 319
344 - If you ever need to change the default root !! 320 If you ever need to change the default root device, video mode,
345 kernel image, use your bootloader's boot op !! 321 ramdisk size, etc. in the kernel image, use the ``rdev`` program (or
346 to recompile the kernel to change these par !! 322 alternatively the LILO boot options when appropriate). No need to
>> 323 recompile the kernel to change these parameters.
347 324
348 - Reboot with the new kernel and enjoy. 325 - Reboot with the new kernel and enjoy.
349 326
350 <<
351 If something goes wrong 327 If something goes wrong
352 ----------------------- 328 -----------------------
353 329
354 If you have problems that seem to be due to ke !! 330 - If you have problems that seem to be due to kernel bugs, please check
355 instructions at 'Documentation/admin-guide/rep !! 331 the file MAINTAINERS to see if there is a particular person associated
>> 332 with the part of the kernel that you are having trouble with. If there
>> 333 isn't anyone listed there, then the second best thing is to mail
>> 334 them to me (torvalds@linux-foundation.org), and possibly to any other
>> 335 relevant mailing-list or to the newsgroup.
>> 336
>> 337 - In all bug-reports, *please* tell what kernel you are talking about,
>> 338 how to duplicate the problem, and what your setup is (use your common
>> 339 sense). If the problem is new, tell me so, and if the problem is
>> 340 old, please try to tell me when you first noticed it.
>> 341
>> 342 - If the bug results in a message like::
>> 343
>> 344 unable to handle kernel paging request at address C0000010
>> 345 Oops: 0002
>> 346 EIP: 0010:XXXXXXXX
>> 347 eax: xxxxxxxx ebx: xxxxxxxx ecx: xxxxxxxx edx: xxxxxxxx
>> 348 esi: xxxxxxxx edi: xxxxxxxx ebp: xxxxxxxx
>> 349 ds: xxxx es: xxxx fs: xxxx gs: xxxx
>> 350 Pid: xx, process nr: xx
>> 351 xx xx xx xx xx xx xx xx xx xx
>> 352
>> 353 or similar kernel debugging information on your screen or in your
>> 354 system log, please duplicate it *exactly*. The dump may look
>> 355 incomprehensible to you, but it does contain information that may
>> 356 help debugging the problem. The text above the dump is also
>> 357 important: it tells something about why the kernel dumped code (in
>> 358 the above example, it's due to a bad kernel pointer). More information
>> 359 on making sense of the dump is in Documentation/admin-guide/oops-tracing.rst
>> 360
>> 361 - If you compiled the kernel with CONFIG_KALLSYMS you can send the dump
>> 362 as is, otherwise you will have to use the ``ksymoops`` program to make
>> 363 sense of the dump (but compiling with CONFIG_KALLSYMS is usually preferred).
>> 364 This utility can be downloaded from
>> 365 ftp://ftp.<country>.kernel.org/pub/linux/utils/kernel/ksymoops/ .
>> 366 Alternatively, you can do the dump lookup by hand:
>> 367
>> 368 - In debugging dumps like the above, it helps enormously if you can
>> 369 look up what the EIP value means. The hex value as such doesn't help
>> 370 me or anybody else very much: it will depend on your particular
>> 371 kernel setup. What you should do is take the hex value from the EIP
>> 372 line (ignore the ``0010:``), and look it up in the kernel namelist to
>> 373 see which kernel function contains the offending address.
>> 374
>> 375 To find out the kernel function name, you'll need to find the system
>> 376 binary associated with the kernel that exhibited the symptom. This is
>> 377 the file 'linux/vmlinux'. To extract the namelist and match it against
>> 378 the EIP from the kernel crash, do::
>> 379
>> 380 nm vmlinux | sort | less
>> 381
>> 382 This will give you a list of kernel addresses sorted in ascending
>> 383 order, from which it is simple to find the function that contains the
>> 384 offending address. Note that the address given by the kernel
>> 385 debugging messages will not necessarily match exactly with the
>> 386 function addresses (in fact, that is very unlikely), so you can't
>> 387 just 'grep' the list: the list will, however, give you the starting
>> 388 point of each kernel function, so by looking for the function that
>> 389 has a starting address lower than the one you are searching for but
>> 390 is followed by a function with a higher address you will find the one
>> 391 you want. In fact, it may be a good idea to include a bit of
>> 392 "context" in your problem report, giving a few lines around the
>> 393 interesting one.
>> 394
>> 395 If you for some reason cannot do the above (you have a pre-compiled
>> 396 kernel image or similar), telling me as much about your setup as
>> 397 possible will help. Please read the :ref:`admin-guide/reporting-bugs.rst <reportingbugs>`
>> 398 document for details.
>> 399
>> 400 - Alternatively, you can use gdb on a running kernel. (read-only; i.e. you
>> 401 cannot change values or set break points.) To do this, first compile the
>> 402 kernel with -g; edit arch/x86/Makefile appropriately, then do a ``make
>> 403 clean``. You'll also need to enable CONFIG_PROC_FS (via ``make config``).
>> 404
>> 405 After you've rebooted with the new kernel, do ``gdb vmlinux /proc/kcore``.
>> 406 You can now use all the usual gdb commands. The command to look up the
>> 407 point where your system crashed is ``l *0xXXXXXXXX``. (Replace the XXXes
>> 408 with the EIP value.)
356 409
357 Hints on understanding kernel bug reports are !! 410 gdb'ing a non-running kernel currently fails because ``gdb`` (wrongly)
358 'Documentation/admin-guide/bug-hunting.rst'. M !! 411 disregards the starting offset for which the kernel is compiled.
359 with gdb is in 'Documentation/dev-tools/gdb-ke <<
360 'Documentation/dev-tools/kgdb.rst'. <<
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