1 .. _readme: 1 .. _readme:
2 2
3 Linux kernel release 6.x <http://kernel.org/> !! 3 Linux kernel release 5.x <http://kernel.org/>
4 ============================================= 4 =============================================
5 5
6 These are the release notes for Linux version !! 6 These are the release notes for Linux version 5. Read them carefully,
7 as they tell you what this is all about, expla 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 8 kernel, and what to do if something goes wrong.
9 9
10 What is Linux? 10 What is Linux?
11 -------------- 11 --------------
12 12
13 Linux is a clone of the operating system Uni 13 Linux is a clone of the operating system Unix, written from scratch by
14 Linus Torvalds with assistance from a loosel 14 Linus Torvalds with assistance from a loosely-knit team of hackers across
15 the Net. It aims towards POSIX and Single UN 15 the Net. It aims towards POSIX and Single UNIX Specification compliance.
16 16
17 It has all the features you would expect in 17 It has all the features you would expect in a modern fully-fledged Unix,
18 including true multitasking, virtual memory, 18 including true multitasking, virtual memory, shared libraries, demand
19 loading, shared copy-on-write executables, p 19 loading, shared copy-on-write executables, proper memory management,
20 and multistack networking including IPv4 and 20 and multistack networking including IPv4 and IPv6.
21 21
22 It is distributed under the GNU General Publ 22 It is distributed under the GNU General Public License v2 - see the
23 accompanying COPYING file for more details. 23 accompanying COPYING file for more details.
24 24
25 On what hardware does it run? 25 On what hardware does it run?
26 ----------------------------- 26 -----------------------------
27 27
28 Although originally developed first for 32-b 28 Although originally developed first for 32-bit x86-based PCs (386 or higher),
29 today Linux also runs on (at least) the Comp 29 today Linux also runs on (at least) the Compaq Alpha AXP, Sun SPARC and
30 UltraSPARC, Motorola 68000, PowerPC, PowerPC 30 UltraSPARC, Motorola 68000, PowerPC, PowerPC64, ARM, Hitachi SuperH, Cell,
31 IBM S/390, MIPS, HP PA-RISC, Intel IA-64, DE 31 IBM S/390, MIPS, HP PA-RISC, Intel IA-64, DEC VAX, AMD x86-64 Xtensa, and
32 ARC architectures. 32 ARC architectures.
33 33
34 Linux is easily portable to most general-pur 34 Linux is easily portable to most general-purpose 32- or 64-bit architectures
35 as long as they have a paged memory manageme 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 Compil 36 GNU C compiler (gcc) (part of The GNU Compiler Collection, GCC). Linux has
37 also been ported to a number of architecture 37 also been ported to a number of architectures without a PMMU, although
38 functionality is then obviously somewhat lim 38 functionality is then obviously somewhat limited.
39 Linux has also been ported to itself. You ca 39 Linux has also been ported to itself. You can now run the kernel as a
40 userspace application - this is called UserM 40 userspace application - this is called UserMode Linux (UML).
41 41
42 Documentation 42 Documentation
43 ------------- 43 -------------
44 44
45 - There is a lot of documentation available b 45 - There is a lot of documentation available both in electronic form on
46 the Internet and in books, both Linux-speci 46 the Internet and in books, both Linux-specific and pertaining to
47 general UNIX questions. I'd recommend look 47 general UNIX questions. I'd recommend looking into the documentation
48 subdirectories on any Linux FTP site for th 48 subdirectories on any Linux FTP site for the LDP (Linux Documentation
49 Project) books. This README is not meant t 49 Project) books. This README is not meant to be documentation on the
50 system: there are much better sources avail 50 system: there are much better sources available.
51 51
52 - There are various README files in the Docum 52 - There are various README files in the Documentation/ subdirectory:
53 these typically contain kernel-specific ins 53 these typically contain kernel-specific installation notes for some
54 drivers for example. Please read the 54 drivers for example. Please read the
55 :ref:`Documentation/process/changes.rst <ch 55 :ref:`Documentation/process/changes.rst <changes>` file, as it
56 contains information about the problems, wh 56 contains information about the problems, which may result by upgrading
57 your kernel. 57 your kernel.
58 58
59 Installing the kernel source 59 Installing the kernel source
60 ---------------------------- 60 ----------------------------
61 61
62 - If you install the full sources, put the ke 62 - If you install the full sources, put the kernel tarball in a
63 directory where you have permissions (e.g. 63 directory where you have permissions (e.g. your home directory) and
64 unpack it:: 64 unpack it::
65 65
66 xz -cd linux-6.x.tar.xz | tar xvf - !! 66 xz -cd linux-5.x.tar.xz | tar xvf -
67 67
68 Replace "X" with the version number of the 68 Replace "X" with the version number of the latest kernel.
69 69
70 Do NOT use the /usr/src/linux area! This ar 70 Do NOT use the /usr/src/linux area! This area has a (usually
71 incomplete) set of kernel headers that are 71 incomplete) set of kernel headers that are used by the library header
72 files. They should match the library, and 72 files. They should match the library, and not get messed up by
73 whatever the kernel-du-jour happens to be. 73 whatever the kernel-du-jour happens to be.
74 74
75 - You can also upgrade between 6.x releases b !! 75 - You can also upgrade between 5.x releases by patching. Patches are
76 distributed in the xz format. To install b 76 distributed in the xz format. To install by patching, get all the
77 newer patch files, enter the top level dire 77 newer patch files, enter the top level directory of the kernel source
78 (linux-6.x) and execute:: !! 78 (linux-5.x) and execute::
79 79
80 xz -cd ../patch-6.x.xz | patch -p1 !! 80 xz -cd ../patch-5.x.xz | patch -p1
81 81
82 Replace "x" for all versions bigger than th 82 Replace "x" for all versions bigger than the version "x" of your current
83 source tree, **in_order**, and you should b 83 source tree, **in_order**, and you should be ok. You may want to remove
84 the backup files (some-file-name~ or some-f 84 the backup files (some-file-name~ or some-file-name.orig), and make sure
85 that there are no failed patches (some-file 85 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 86 If there are, either you or I have made a mistake.
87 87
88 Unlike patches for the 6.x kernels, patches !! 88 Unlike patches for the 5.x kernels, patches for the 5.x.y kernels
89 (also known as the -stable kernels) are not 89 (also known as the -stable kernels) are not incremental but instead apply
90 directly to the base 6.x kernel. For examp !! 90 directly to the base 5.x kernel. For example, if your base kernel is 5.0
91 and you want to apply the 6.0.3 patch, you !! 91 and you want to apply the 5.0.3 patch, you must not first apply the 5.0.1
92 and 6.0.2 patches. Similarly, if you are ru !! 92 and 5.0.2 patches. Similarly, if you are running kernel version 5.0.2 and
93 want to jump to 6.0.3, you must first rever !! 93 want to jump to 5.0.3, you must first reverse the 5.0.2 patch (that is,
94 patch -R) **before** applying the 6.0.3 pat !! 94 patch -R) **before** applying the 5.0.3 patch. You can read more on this in
95 :ref:`Documentation/process/applying-patche 95 :ref:`Documentation/process/applying-patches.rst <applying_patches>`.
96 96
97 Alternatively, the script patch-kernel can 97 Alternatively, the script patch-kernel can be used to automate this
98 process. It determines the current kernel 98 process. It determines the current kernel version and applies any
99 patches found:: 99 patches found::
100 100
101 linux/scripts/patch-kernel linux 101 linux/scripts/patch-kernel linux
102 102
103 The first argument in the command above is 103 The first argument in the command above is the location of the
104 kernel source. Patches are applied from th 104 kernel source. Patches are applied from the current directory, but
105 an alternative directory can be specified a 105 an alternative directory can be specified as the second argument.
106 106
107 - Make sure you have no stale .o files and de 107 - Make sure you have no stale .o files and dependencies lying around::
108 108
109 cd linux 109 cd linux
110 make mrproper 110 make mrproper
111 111
112 You should now have the sources correctly i 112 You should now have the sources correctly installed.
113 113
114 Software requirements 114 Software requirements
115 --------------------- 115 ---------------------
116 116
117 Compiling and running the 6.x kernels requi !! 117 Compiling and running the 5.x kernels requires up-to-date
118 versions of various software packages. Con 118 versions of various software packages. Consult
119 :ref:`Documentation/process/changes.rst <ch 119 :ref:`Documentation/process/changes.rst <changes>` for the minimum version numbers
120 required and how to get updates for these p 120 required and how to get updates for these packages. Beware that using
121 excessively old versions of these packages 121 excessively old versions of these packages can cause indirect
122 errors that are very difficult to track dow 122 errors that are very difficult to track down, so don't assume that
123 you can just update packages when obvious p 123 you can just update packages when obvious problems arise during
124 build or operation. 124 build or operation.
125 125
126 Build directory for the kernel 126 Build directory for the kernel
127 ------------------------------ 127 ------------------------------
128 128
129 When compiling the kernel, all output files 129 When compiling the kernel, all output files will per default be
130 stored together with the kernel source code 130 stored together with the kernel source code.
131 Using the option ``make O=output/dir`` allo 131 Using the option ``make O=output/dir`` allows you to specify an alternate
132 place for the output files (including .conf 132 place for the output files (including .config).
133 Example:: 133 Example::
134 134
135 kernel source code: /usr/src/linux-6.x !! 135 kernel source code: /usr/src/linux-5.x
136 build directory: /home/name/build/kern 136 build directory: /home/name/build/kernel
137 137
138 To configure and build the kernel, use:: 138 To configure and build the kernel, use::
139 139
140 cd /usr/src/linux-6.x !! 140 cd /usr/src/linux-5.x
141 make O=/home/name/build/kernel menuconfig 141 make O=/home/name/build/kernel menuconfig
142 make O=/home/name/build/kernel 142 make O=/home/name/build/kernel
143 sudo make O=/home/name/build/kernel modul 143 sudo make O=/home/name/build/kernel modules_install install
144 144
145 Please note: If the ``O=output/dir`` option 145 Please note: If the ``O=output/dir`` option is used, then it must be
146 used for all invocations of make. 146 used for all invocations of make.
147 147
148 Configuring the kernel 148 Configuring the kernel
149 ---------------------- 149 ----------------------
150 150
151 Do not skip this step even if you are only 151 Do not skip this step even if you are only upgrading one minor
152 version. New configuration options are add 152 version. New configuration options are added in each release, and
153 odd problems will turn up if the configurat 153 odd problems will turn up if the configuration files are not set up
154 as expected. If you want to carry your exi 154 as expected. If you want to carry your existing configuration to a
155 new version with minimal work, use ``make o 155 new version with minimal work, use ``make oldconfig``, which will
156 only ask you for the answers to new questio 156 only ask you for the answers to new questions.
157 157
158 - Alternative configuration commands are:: 158 - Alternative configuration commands are::
159 159
160 "make config" Plain text interface. 160 "make config" Plain text interface.
161 161
162 "make menuconfig" Text based color menus 162 "make menuconfig" Text based color menus, radiolists & dialogs.
163 163
164 "make nconfig" Enhanced text based co 164 "make nconfig" Enhanced text based color menus.
165 165
166 "make xconfig" Qt based configuration 166 "make xconfig" Qt based configuration tool.
167 167
168 "make gconfig" GTK+ based configurati 168 "make gconfig" GTK+ based configuration tool.
169 169
170 "make oldconfig" Default all questions 170 "make oldconfig" Default all questions based on the contents of
171 your existing ./.confi 171 your existing ./.config file and asking about
172 new config symbols. 172 new config symbols.
173 173
174 "make olddefconfig" 174 "make olddefconfig"
175 Like above, but sets n 175 Like above, but sets new symbols to their default
176 values without prompti 176 values without prompting.
177 177
178 "make defconfig" Create a ./.config fil 178 "make defconfig" Create a ./.config file by using the default
179 symbol values from eit 179 symbol values from either arch/$ARCH/defconfig
180 or arch/$ARCH/configs/ 180 or arch/$ARCH/configs/${PLATFORM}_defconfig,
181 depending on the archi 181 depending on the architecture.
182 182
183 "make ${PLATFORM}_defconfig" 183 "make ${PLATFORM}_defconfig"
184 Create a ./.config fil 184 Create a ./.config file by using the default
185 symbol values from 185 symbol values from
186 arch/$ARCH/configs/${P 186 arch/$ARCH/configs/${PLATFORM}_defconfig.
187 Use "make help" to get 187 Use "make help" to get a list of all available
188 platforms of your arch 188 platforms of your architecture.
189 189
190 "make allyesconfig" 190 "make allyesconfig"
191 Create a ./.config fil 191 Create a ./.config file by setting symbol
192 values to 'y' as much 192 values to 'y' as much as possible.
193 193
194 "make allmodconfig" 194 "make allmodconfig"
195 Create a ./.config fil 195 Create a ./.config file by setting symbol
196 values to 'm' as much 196 values to 'm' as much as possible.
197 197
198 "make allnoconfig" Create a ./.config fil 198 "make allnoconfig" Create a ./.config file by setting symbol
199 values to 'n' as much 199 values to 'n' as much as possible.
200 200
201 "make randconfig" Create a ./.config fil 201 "make randconfig" Create a ./.config file by setting symbol
202 values to random value 202 values to random values.
203 203
204 "make localmodconfig" Create a config bas 204 "make localmodconfig" Create a config based on current config and
205 loaded modules (lsm 205 loaded modules (lsmod). Disables any module
206 option that is not 206 option that is not needed for the loaded modules.
207 207
208 To create a localmo 208 To create a localmodconfig for another machine,
209 store the lsmod of 209 store the lsmod of that machine into a file
210 and pass it in as a 210 and pass it in as a LSMOD parameter.
211 211
212 Also, you can prese 212 Also, you can preserve modules in certain folders
213 or kconfig files by 213 or kconfig files by specifying their paths in
214 parameter LMC_KEEP. 214 parameter LMC_KEEP.
215 215
216 target$ lsmod > /tmp/mylsmo 216 target$ lsmod > /tmp/mylsmod
217 target$ scp /tmp/mylsmod ho 217 target$ scp /tmp/mylsmod host:/tmp
218 218
219 host$ make LSMOD=/tmp/mylsm 219 host$ make LSMOD=/tmp/mylsmod \
220 LMC_KEEP="drivers/u 220 LMC_KEEP="drivers/usb:drivers/gpu:fs" \
221 localmodconfig 221 localmodconfig
222 222
223 The above also work 223 The above also works when cross compiling.
224 224
225 "make localyesconfig" Similar to localmod 225 "make localyesconfig" Similar to localmodconfig, except it will convert
226 all module options 226 all module options to built in (=y) options. You can
227 also preserve modul 227 also preserve modules by LMC_KEEP.
228 228
229 "make kvm_guest.config" Enable addition 229 "make kvm_guest.config" Enable additional options for kvm guest kernel
230 support. 230 support.
231 231
232 "make xen.config" Enable additional opt 232 "make xen.config" Enable additional options for xen dom0 guest kernel
233 support. 233 support.
234 234
235 "make tinyconfig" Configure the tiniest 235 "make tinyconfig" Configure the tiniest possible kernel.
236 236
237 You can find more information on using the 237 You can find more information on using the Linux kernel config tools
238 in Documentation/kbuild/kconfig.rst. 238 in Documentation/kbuild/kconfig.rst.
239 239
240 - NOTES on ``make config``: 240 - NOTES on ``make config``:
241 241
242 - Having unnecessary drivers will make the 242 - Having unnecessary drivers will make the kernel bigger, and can
243 under some circumstances lead to problem 243 under some circumstances lead to problems: probing for a
244 nonexistent controller card may confuse 244 nonexistent controller card may confuse your other controllers.
245 245
246 - A kernel with math-emulation compiled in 246 - A kernel with math-emulation compiled in will still use the
247 coprocessor if one is present: the math 247 coprocessor if one is present: the math emulation will just
248 never get used in that case. The kernel 248 never get used in that case. The kernel will be slightly larger,
249 but will work on different machines rega 249 but will work on different machines regardless of whether they
250 have a math coprocessor or not. 250 have a math coprocessor or not.
251 251
252 - The "kernel hacking" configuration detai 252 - The "kernel hacking" configuration details usually result in a
253 bigger or slower kernel (or both), and c 253 bigger or slower kernel (or both), and can even make the kernel
254 less stable by configuring some routines 254 less stable by configuring some routines to actively try to
255 break bad code to find kernel problems ( 255 break bad code to find kernel problems (kmalloc()). Thus you
256 should probably answer 'n' to the questi 256 should probably answer 'n' to the questions for "development",
257 "experimental", or "debugging" features. 257 "experimental", or "debugging" features.
258 258
259 Compiling the kernel 259 Compiling the kernel
260 -------------------- 260 --------------------
261 261
262 - Make sure you have at least gcc 5.1 availab !! 262 - Make sure you have at least gcc 4.9 available.
263 For more information, refer to :ref:`Docume 263 For more information, refer to :ref:`Documentation/process/changes.rst <changes>`.
264 264
265 - Do a ``make`` to create a compressed kernel !! 265 Please note that you can still run a.out user programs with this kernel.
266 ``make install`` if you have lilo installed !! 266
267 install script recognised by the kernel's i !! 267 - Do a ``make`` to create a compressed kernel image. It is also
268 distributions will have a recognized instal !! 268 possible to do ``make install`` if you have lilo installed to suit the
269 check your distribution's setup first. !! 269 kernel makefiles, but you may want to check your particular lilo setup first.
270 270
271 To do the actual install, you have to be ro 271 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 272 build should require that. Don't take the name of root in vain.
273 273
274 - If you configured any of the parts of the k 274 - If you configured any of the parts of the kernel as ``modules``, you
275 will also have to do ``make modules_install 275 will also have to do ``make modules_install``.
276 276
277 - Verbose kernel compile/build output: 277 - Verbose kernel compile/build output:
278 278
279 Normally, the kernel build system runs in a 279 Normally, the kernel build system runs in a fairly quiet mode (but not
280 totally silent). However, sometimes you or 280 totally silent). However, sometimes you or other kernel developers need
281 to see compile, link, or other commands exa 281 to see compile, link, or other commands exactly as they are executed.
282 For this, use "verbose" build mode. This i 282 For this, use "verbose" build mode. This is done by passing
283 ``V=1`` to the ``make`` command, e.g.:: 283 ``V=1`` to the ``make`` command, e.g.::
284 284
285 make V=1 all 285 make V=1 all
286 286
287 To have the build system also tell the reas 287 To have the build system also tell the reason for the rebuild of each
288 target, use ``V=2``. The default is ``V=0` 288 target, use ``V=2``. The default is ``V=0``.
289 289
290 - Keep a backup kernel handy in case somethin 290 - Keep a backup kernel handy in case something goes wrong. This is
291 especially true for the development release 291 especially true for the development releases, since each new release
292 contains new code which has not been debugg 292 contains new code which has not been debugged. Make sure you keep a
293 backup of the modules corresponding to that 293 backup of the modules corresponding to that kernel, as well. If you
294 are installing a new kernel with the same v 294 are installing a new kernel with the same version number as your
295 working kernel, make a backup of your modul 295 working kernel, make a backup of your modules directory before you
296 do a ``make modules_install``. 296 do a ``make modules_install``.
297 297
298 Alternatively, before compiling, use the ke 298 Alternatively, before compiling, use the kernel config option
299 "LOCALVERSION" to append a unique suffix to 299 "LOCALVERSION" to append a unique suffix to the regular kernel version.
300 LOCALVERSION can be set in the "General Set 300 LOCALVERSION can be set in the "General Setup" menu.
301 301
302 - In order to boot your new kernel, you'll ne 302 - In order to boot your new kernel, you'll need to copy the kernel
303 image (e.g. .../linux/arch/x86/boot/bzImage 303 image (e.g. .../linux/arch/x86/boot/bzImage after compilation)
304 to the place where your regular bootable ke 304 to the place where your regular bootable kernel is found.
305 305
306 - Booting a kernel directly from a storage de !! 306 - Booting a kernel directly from a floppy without the assistance of a
307 of a bootloader such as LILO or GRUB, is no !! 307 bootloader such as LILO, is no longer supported.
308 (non-EFI systems). On UEFI/EFI systems, how !! 308
309 which allows the motherboard to boot direct !! 309 If you boot Linux from the hard drive, chances are you use LILO, which
310 On modern workstations and desktops, it's g !! 310 uses the kernel image as specified in the file /etc/lilo.conf. The
311 bootloader as difficulties can arise with m !! 311 kernel image file is usually /vmlinuz, /boot/vmlinuz, /bzImage or
312 For more details on EFISTUB, !! 312 /boot/bzImage. To use the new kernel, save a copy of the old image
313 see "Documentation/admin-guide/efi-stub.rst !! 313 and copy the new image over the old one. Then, you MUST RERUN LILO
314 !! 314 to update the loading map! If you don't, you won't be able to boot
315 - It's important to note that as of 2016 LILO !! 315 the new kernel image.
316 active development, though as it was extrem !! 316
317 in documentation. Popular alternatives incl !! 317 Reinstalling LILO is usually a matter of running /sbin/lilo.
318 systemd-boot, or EFISTUB. For various reaso !! 318 You may wish to edit /etc/lilo.conf to specify an entry for your
319 software that's no longer in active develop !! 319 old kernel image (say, /vmlinux.old) in case the new one does not
320 !! 320 work. See the LILO docs for more information.
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. <<
340 321
341 - After reinstalling LILO, you should be all !! 322 After reinstalling LILO, you should be all set. Shutdown the system,
342 reboot, and enjoy! 323 reboot, and enjoy!
343 324
344 - If you ever need to change the default root !! 325 If you ever need to change the default root device, video mode,
345 kernel image, use your bootloader's boot op !! 326 etc. in the kernel image, use your bootloader's boot options
346 to recompile the kernel to change these par !! 327 where appropriate. No need to recompile the kernel to change
>> 328 these parameters.
347 329
348 - Reboot with the new kernel and enjoy. 330 - Reboot with the new kernel and enjoy.
349 331
350 <<
351 If something goes wrong 332 If something goes wrong
352 ----------------------- 333 -----------------------
353 334
354 If you have problems that seem to be due to ke !! 335 - If you have problems that seem to be due to kernel bugs, please check
355 instructions at 'Documentation/admin-guide/rep !! 336 the file MAINTAINERS to see if there is a particular person associated
>> 337 with the part of the kernel that you are having trouble with. If there
>> 338 isn't anyone listed there, then the second best thing is to mail
>> 339 them to me (torvalds@linux-foundation.org), and possibly to any other
>> 340 relevant mailing-list or to the newsgroup.
>> 341
>> 342 - In all bug-reports, *please* tell what kernel you are talking about,
>> 343 how to duplicate the problem, and what your setup is (use your common
>> 344 sense). If the problem is new, tell me so, and if the problem is
>> 345 old, please try to tell me when you first noticed it.
>> 346
>> 347 - If the bug results in a message like::
>> 348
>> 349 unable to handle kernel paging request at address C0000010
>> 350 Oops: 0002
>> 351 EIP: 0010:XXXXXXXX
>> 352 eax: xxxxxxxx ebx: xxxxxxxx ecx: xxxxxxxx edx: xxxxxxxx
>> 353 esi: xxxxxxxx edi: xxxxxxxx ebp: xxxxxxxx
>> 354 ds: xxxx es: xxxx fs: xxxx gs: xxxx
>> 355 Pid: xx, process nr: xx
>> 356 xx xx xx xx xx xx xx xx xx xx
>> 357
>> 358 or similar kernel debugging information on your screen or in your
>> 359 system log, please duplicate it *exactly*. The dump may look
>> 360 incomprehensible to you, but it does contain information that may
>> 361 help debugging the problem. The text above the dump is also
>> 362 important: it tells something about why the kernel dumped code (in
>> 363 the above example, it's due to a bad kernel pointer). More information
>> 364 on making sense of the dump is in Documentation/admin-guide/bug-hunting.rst
>> 365
>> 366 - If you compiled the kernel with CONFIG_KALLSYMS you can send the dump
>> 367 as is, otherwise you will have to use the ``ksymoops`` program to make
>> 368 sense of the dump (but compiling with CONFIG_KALLSYMS is usually preferred).
>> 369 This utility can be downloaded from
>> 370 https://www.kernel.org/pub/linux/utils/kernel/ksymoops/ .
>> 371 Alternatively, you can do the dump lookup by hand:
>> 372
>> 373 - In debugging dumps like the above, it helps enormously if you can
>> 374 look up what the EIP value means. The hex value as such doesn't help
>> 375 me or anybody else very much: it will depend on your particular
>> 376 kernel setup. What you should do is take the hex value from the EIP
>> 377 line (ignore the ``0010:``), and look it up in the kernel namelist to
>> 378 see which kernel function contains the offending address.
>> 379
>> 380 To find out the kernel function name, you'll need to find the system
>> 381 binary associated with the kernel that exhibited the symptom. This is
>> 382 the file 'linux/vmlinux'. To extract the namelist and match it against
>> 383 the EIP from the kernel crash, do::
>> 384
>> 385 nm vmlinux | sort | less
>> 386
>> 387 This will give you a list of kernel addresses sorted in ascending
>> 388 order, from which it is simple to find the function that contains the
>> 389 offending address. Note that the address given by the kernel
>> 390 debugging messages will not necessarily match exactly with the
>> 391 function addresses (in fact, that is very unlikely), so you can't
>> 392 just 'grep' the list: the list will, however, give you the starting
>> 393 point of each kernel function, so by looking for the function that
>> 394 has a starting address lower than the one you are searching for but
>> 395 is followed by a function with a higher address you will find the one
>> 396 you want. In fact, it may be a good idea to include a bit of
>> 397 "context" in your problem report, giving a few lines around the
>> 398 interesting one.
>> 399
>> 400 If you for some reason cannot do the above (you have a pre-compiled
>> 401 kernel image or similar), telling me as much about your setup as
>> 402 possible will help. Please read
>> 403 'Documentation/admin-guide/reporting-issues.rst' for details.
>> 404
>> 405 - Alternatively, you can use gdb on a running kernel. (read-only; i.e. you
>> 406 cannot change values or set break points.) To do this, first compile the
>> 407 kernel with -g; edit arch/x86/Makefile appropriately, then do a ``make
>> 408 clean``. You'll also need to enable CONFIG_PROC_FS (via ``make config``).
>> 409
>> 410 After you've rebooted with the new kernel, do ``gdb vmlinux /proc/kcore``.
>> 411 You can now use all the usual gdb commands. The command to look up the
>> 412 point where your system crashed is ``l *0xXXXXXXXX``. (Replace the XXXes
>> 413 with the EIP value.)
356 414
357 Hints on understanding kernel bug reports are !! 415 gdb'ing a non-running kernel currently fails because ``gdb`` (wrongly)
358 'Documentation/admin-guide/bug-hunting.rst'. M !! 416 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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