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1.. _readme:
2
3Linux kernel release 6.x <http://kernel.org/>
4=============================================
5
6These are the release notes for Linux version 6. Read them carefully,
7as they tell you what this is all about, explain how to install the
8kernel, and what to do if something goes wrong.
9
10What is Linux?
11--------------
12
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.
16
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.
21
22 It is distributed under the GNU General Public License v2 - see the
23 accompanying COPYING file for more details.
24
25On what hardware does it run?
26-----------------------------
27
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
32 ARC architectures.
33
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).
41
42Documentation
43-------------
44
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.
51
52 - There are various README files in the Documentation/ subdirectory:
53 these typically contain kernel-specific installation notes for some
54 drivers for example. Please read the
55 :ref:`Documentation/process/changes.rst <changes>` file, as it
56 contains information about the problems, which may result by upgrading
57 your kernel.
58
59Installing the kernel source
60----------------------------
61
62 - If you install the full sources, put the kernel tarball in a
63 directory where you have permissions (e.g. your home directory) and
64 unpack it::
65
66 xz -cd linux-6.x.tar.xz | tar xvf -
67
68 Replace "X" with the version number of the latest kernel.
69
70 Do NOT use the /usr/src/linux area! This area has a (usually
71 incomplete) set of kernel headers that are used by the library header
72 files. They should match the library, and not get messed up by
73 whatever the kernel-du-jour happens to be.
74
75 - You can also upgrade between 6.x releases by patching. Patches are
76 distributed in the xz format. To install by patching, get all the
77 newer patch files, enter the top level directory of the kernel source
78 (linux-6.x) and execute::
79
80 xz -cd ../patch-6.x.xz | patch -p1
81
82 Replace "x" for all versions bigger than the version "x" of your current
83 source tree, **in_order**, and you should be ok. You may want to remove
84 the backup files (some-file-name~ or some-file-name.orig), and make sure
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 mistake.
87
88 Unlike patches for the 6.x kernels, patches for the 6.x.y kernels
89 (also known as the -stable kernels) are not incremental but instead apply
90 directly to the base 6.x kernel. For example, if your base kernel is 6.0
91 and you want to apply the 6.0.3 patch, you must not first apply the 6.0.1
92 and 6.0.2 patches. Similarly, if you are running kernel version 6.0.2 and
93 want to jump to 6.0.3, you must first reverse the 6.0.2 patch (that is,
94 patch -R) **before** applying the 6.0.3 patch. You can read more on this in
95 :ref:`Documentation/process/applying-patches.rst <applying_patches>`.
96
97 Alternatively, the script patch-kernel can be used to automate this
98 process. It determines the current kernel version and applies any
99 patches found::
100
101 linux/scripts/patch-kernel linux
102
103 The first argument in the command above is the location of the
104 kernel source. Patches are applied from the current directory, but
105 an alternative directory can be specified as the second argument.
106
107 - Make sure you have no stale .o files and dependencies lying around::
108
109 cd linux
110 make mrproper
111
112 You should now have the sources correctly installed.
113
114Software requirements
115---------------------
116
117 Compiling and running the 6.x kernels requires up-to-date
118 versions of various software packages. Consult
119 :ref:`Documentation/process/changes.rst <changes>` for the minimum version numbers
120 required and how to get updates for these packages. Beware that using
121 excessively old versions of these packages can cause indirect
122 errors that are very difficult to track down, so don't assume that
123 you can just update packages when obvious problems arise during
124 build or operation.
125
126Build directory for the kernel
127------------------------------
128
129 When compiling the kernel, all output files will per default be
130 stored together with the kernel source code.
131 Using the option ``make O=output/dir`` allows you to specify an alternate
132 place for the output files (including .config).
133 Example::
134
135 kernel source code: /usr/src/linux-6.x
136 build directory: /home/name/build/kernel
137
138 To configure and build the kernel, use::
139
140 cd /usr/src/linux-6.x
141 make O=/home/name/build/kernel menuconfig
142 make O=/home/name/build/kernel
143 sudo make O=/home/name/build/kernel modules_install install
144
145 Please note: If the ``O=output/dir`` option is used, then it must be
146 used for all invocations of make.
147
148Configuring the kernel
149----------------------
150
151 Do not skip this step even if you are only upgrading one minor
152 version. New configuration options are added in each release, and
153 odd problems will turn up if the configuration files are not set up
154 as expected. If you want to carry your existing configuration to a
155 new version with minimal work, use ``make oldconfig``, which will
156 only ask you for the answers to new questions.
157
158 - Alternative configuration commands are::
159
160 "make config" Plain text interface.
161
162 "make menuconfig" Text based color menus, radiolists & dialogs.
163
164 "make nconfig" Enhanced text based color menus.
165
166 "make xconfig" Qt based configuration tool.
167
168 "make gconfig" GTK+ based configuration tool.
169
170 "make oldconfig" Default all questions based on the contents of
171 your existing ./.config file and asking about
172 new config symbols.
173
174 "make olddefconfig"
175 Like above, but sets new symbols to their default
176 values without prompting.
177
178 "make defconfig" Create a ./.config file by using the default
179 symbol values from either arch/$ARCH/defconfig
180 or arch/$ARCH/configs/${PLATFORM}_defconfig,
181 depending on the architecture.
182
183 "make ${PLATFORM}_defconfig"
184 Create a ./.config file by using the default
185 symbol values from
186 arch/$ARCH/configs/${PLATFORM}_defconfig.
187 Use "make help" to get a list of all available
188 platforms of your architecture.
189
190 "make allyesconfig"
191 Create a ./.config file by setting symbol
192 values to 'y' as much as possible.
193
194 "make allmodconfig"
195 Create a ./.config file by setting symbol
196 values to 'm' as much as possible.
197
198 "make allnoconfig" Create a ./.config file by setting symbol
199 values to 'n' as much as possible.
200
201 "make randconfig" Create a ./.config file by setting symbol
202 values to random values.
203
204 "make localmodconfig" Create a config based on current config and
205 loaded modules (lsmod). Disables any module
206 option that is not needed for the loaded modules.
207
208 To create a localmodconfig for another machine,
209 store the lsmod of that machine into a file
210 and pass it in as a LSMOD parameter.
211
212 Also, you can preserve modules in certain folders
213 or kconfig files by specifying their paths in
214 parameter LMC_KEEP.
215
216 target$ lsmod > /tmp/mylsmod
217 target$ scp /tmp/mylsmod host:/tmp
218
219 host$ make LSMOD=/tmp/mylsmod \
220 LMC_KEEP="drivers/usb:drivers/gpu:fs" \
221 localmodconfig
222
223 The above also works when cross compiling.
224
225 "make localyesconfig" Similar to localmodconfig, except it will convert
226 all module options to built in (=y) options. You can
227 also preserve modules by LMC_KEEP.
228
229 "make kvm_guest.config" Enable additional options for kvm guest kernel
230 support.
231
232 "make xen.config" Enable additional options for xen dom0 guest kernel
233 support.
234
235 "make tinyconfig" Configure the tiniest possible kernel.
236
237 You can find more information on using the Linux kernel config tools
238 in Documentation/kbuild/kconfig.rst.
239
240 - NOTES on ``make config``:
241
242 - Having unnecessary drivers will make the kernel bigger, and can
243 under some circumstances lead to problems: probing for a
244 nonexistent controller card may confuse your other controllers.
245
246 - A kernel with math-emulation compiled in will still use the
247 coprocessor if one is present: the math emulation will just
248 never get used in that case. The kernel will be slightly larger,
249 but will work on different machines regardless of whether they
250 have a math coprocessor or not.
251
252 - The "kernel hacking" configuration details usually result in a
253 bigger or slower kernel (or both), and can even make the kernel
254 less stable by configuring some routines to actively try to
255 break bad code to find kernel problems (kmalloc()). Thus you
256 should probably answer 'n' to the questions for "development",
257 "experimental", or "debugging" features.
258
259Compiling the kernel
260--------------------
261
262 - Make sure you have at least gcc 5.1 available.
263 For more information, refer to :ref:`Documentation/process/changes.rst <changes>`.
264
265 - Do a ``make`` to create a compressed kernel image. It is also possible to do
266 ``make install`` if you have lilo installed or if your distribution has an
267 install script recognised by the kernel's installer. Most popular
268 distributions will have a recognized install script. You may want to
269 check your distribution's setup first.
270
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 name of root in vain.
273
274 - If you configured any of the parts of the kernel as ``modules``, you
275 will also have to do ``make modules_install``.
276
277 - Verbose kernel compile/build output:
278
279 Normally, the kernel build system runs in a fairly quiet mode (but not
280 totally silent). However, sometimes you or other kernel developers need
281 to see compile, link, or other commands exactly as they are executed.
282 For this, use "verbose" build mode. This is done by passing
283 ``V=1`` to the ``make`` command, e.g.::
284
285 make V=1 all
286
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``.
289
290 - Keep a backup kernel handy in case something goes wrong. This is
291 especially true for the development releases, since each new release
292 contains new code which has not been debugged. Make sure you keep a
293 backup of the modules corresponding to that kernel, as well. If you
294 are installing a new kernel with the same version number as your
295 working kernel, make a backup of your modules directory before you
296 do a ``make modules_install``.
297
298 Alternatively, before compiling, use the kernel config option
299 "LOCALVERSION" to append a unique suffix to the regular kernel version.
300 LOCALVERSION can be set in the "General Setup" menu.
301
302 - In order to boot your new kernel, you'll need to copy the kernel
303 image (e.g. .../linux/arch/x86/boot/bzImage after compilation)
304 to the place where your regular bootable kernel is found.
305
306 - Booting a kernel directly from a storage device without the assistance
307 of a bootloader such as LILO or GRUB, is no longer supported in BIOS
308 (non-EFI systems). On UEFI/EFI systems, however, you can use EFISTUB
309 which allows the motherboard to boot directly to the kernel.
310 On modern workstations and desktops, it's generally recommended to use a
311 bootloader as difficulties can arise with multiple kernels and secure boot.
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 (LInux LOader) is no longer in
316 active development, though as it was extremely popular, it often comes up
317 in documentation. Popular alternatives include GRUB2, rEFInd, Syslinux,
318 systemd-boot, or EFISTUB. For various reasons, it's not recommended to use
319 software that's no longer in active development.
320
321 - Chances are your distribution includes an install script and running
322 ``make install`` will be all that's needed. Should that not be the case
323 you'll have to identify your bootloader and reference its documentation or
324 configure your EFI.
325
326Legacy LILO Instructions
327------------------------
328
329
330 - If you use LILO the kernel images are specified in the file /etc/lilo.conf.
331 The kernel image file is usually /vmlinuz, /boot/vmlinuz, /bzImage or
332 /boot/bzImage. To use the new kernel, save a copy of the old image and copy
333 the new image over the old one. Then, you MUST RERUN LILO to update the
334 loading map! If you don't, you won't be able to boot the new kernel image.
335
336 - Reinstalling LILO is usually a matter of running /sbin/lilo. You may wish
337 to edit /etc/lilo.conf to specify an entry for your old kernel image
338 (say, /vmlinux.old) in case the new one does not work. See the LILO docs
339 for more information.
340
341 - After reinstalling LILO, you should be all set. Shutdown the system,
342 reboot, and enjoy!
343
344 - If you ever need to change the default root device, video mode, etc. in the
345 kernel image, use your bootloader's boot options where appropriate. No need
346 to recompile the kernel to change these parameters.
347
348 - Reboot with the new kernel and enjoy.
349
350
351If something goes wrong
352-----------------------
353
354If you have problems that seem to be due to kernel bugs, please follow the
355instructions at 'Documentation/admin-guide/reporting-issues.rst'.
356
357Hints on understanding kernel bug reports are in
358'Documentation/admin-guide/bug-hunting.rst'. More on debugging the kernel
359with gdb is in 'Documentation/dev-tools/gdb-kernel-debugging.rst' and
360'Documentation/dev-tools/kgdb.rst'.
1Linux kernel release 4.x <http://kernel.org/>
2=============================================
3
4These are the release notes for Linux version 4. Read them carefully,
5as they tell you what this is all about, explain how to install the
6kernel, and what to do if something goes wrong.
7
8What 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 - see the
21 accompanying COPYING file for more details.
22
23On 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, AVR32, 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
40Documentation
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 - 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
64Installing the kernel source
65----------------------------
66
67 - If you install the full sources, put the kernel tarball in a
68 directory where you have permissions (e.g. your home directory) and
69 unpack it::
70
71 xz -cd linux-4.X.tar.xz | tar xvf -
72
73 Replace "X" with the version number of the latest kernel.
74
75 Do NOT use the /usr/src/linux area! This area has a (usually
76 incomplete) set of kernel headers that are used by the library header
77 files. They should match the library, and not get messed up by
78 whatever the kernel-du-jour happens to be.
79
80 - You can also upgrade between 4.x releases by patching. Patches are
81 distributed in the xz format. To install by patching, get all the
82 newer patch files, enter the top level directory of the kernel source
83 (linux-4.X) and execute::
84
85 xz -cd ../patch-4.x.xz | patch -p1
86
87 Replace "x" for all versions bigger than the version "X" of your current
88 source tree, **in_order**, and you should be ok. You may want to remove
89 the backup files (some-file-name~ or some-file-name.orig), and make sure
90 that there are no failed patches (some-file-name# or some-file-name.rej).
91 If there are, either you or I have made a mistake.
92
93 Unlike patches for the 4.x kernels, patches for the 4.x.y kernels
94 (also known as the -stable kernels) are not incremental but instead apply
95 directly to the base 4.x kernel. For example, if your base kernel is 4.0
96 and you want to apply the 4.0.3 patch, you must not first apply the 4.0.1
97 and 4.0.2 patches. Similarly, if you are running kernel version 4.0.2 and
98 want to jump to 4.0.3, you must first reverse the 4.0.2 patch (that is,
99 patch -R) **before** applying the 4.0.3 patch. You can read more on this in
100 :ref:`Documentation/process/applying-patches.rst <applying_patches>`.
101
102 Alternatively, the script patch-kernel can be used to automate this
103 process. It determines the current kernel version and applies any
104 patches found::
105
106 linux/scripts/patch-kernel linux
107
108 The first argument in the command above is the location of the
109 kernel source. Patches are applied from the current directory, but
110 an alternative directory can be specified as the second argument.
111
112 - Make sure you have no stale .o files and dependencies lying around::
113
114 cd linux
115 make mrproper
116
117 You should now have the sources correctly installed.
118
119Software requirements
120---------------------
121
122 Compiling and running the 4.x kernels requires up-to-date
123 versions of various software packages. Consult
124 :ref:`Documentation/process/changes.rst <changes>` for the minimum version numbers
125 required and how to get updates for these packages. Beware that using
126 excessively old versions of these packages can cause indirect
127 errors that are very difficult to track down, so don't assume that
128 you can just update packages when obvious problems arise during
129 build or operation.
130
131Build directory for the kernel
132------------------------------
133
134 When compiling the kernel, all output files will per default be
135 stored together with the kernel source code.
136 Using the option ``make O=output/dir`` allows you to specify an alternate
137 place for the output files (including .config).
138 Example::
139
140 kernel source code: /usr/src/linux-4.X
141 build directory: /home/name/build/kernel
142
143 To configure and build the kernel, use::
144
145 cd /usr/src/linux-4.X
146 make O=/home/name/build/kernel menuconfig
147 make O=/home/name/build/kernel
148 sudo make O=/home/name/build/kernel modules_install install
149
150 Please note: If the ``O=output/dir`` option is used, then it must be
151 used for all invocations of make.
152
153Configuring the kernel
154----------------------
155
156 Do not skip this step even if you are only upgrading one minor
157 version. New configuration options are added in each release, and
158 odd problems will turn up if the configuration files are not set up
159 as expected. If you want to carry your existing configuration to a
160 new version with minimal work, use ``make oldconfig``, which will
161 only ask you for the answers to new questions.
162
163 - Alternative configuration commands are::
164
165 "make config" Plain text interface.
166
167 "make menuconfig" Text based color menus, radiolists & dialogs.
168
169 "make nconfig" Enhanced text based color menus.
170
171 "make xconfig" Qt based configuration tool.
172
173 "make gconfig" GTK+ based configuration tool.
174
175 "make oldconfig" Default all questions based on the contents of
176 your existing ./.config file and asking about
177 new config symbols.
178
179 "make silentoldconfig"
180 Like above, but avoids cluttering the screen
181 with questions already answered.
182 Additionally updates the dependencies.
183
184 "make olddefconfig"
185 Like above, but sets new symbols to their default
186 values without prompting.
187
188 "make defconfig" Create a ./.config file by using the default
189 symbol values from either arch/$ARCH/defconfig
190 or arch/$ARCH/configs/${PLATFORM}_defconfig,
191 depending on the architecture.
192
193 "make ${PLATFORM}_defconfig"
194 Create a ./.config file by using the default
195 symbol values from
196 arch/$ARCH/configs/${PLATFORM}_defconfig.
197 Use "make help" to get a list of all available
198 platforms of your architecture.
199
200 "make allyesconfig"
201 Create a ./.config file by setting symbol
202 values to 'y' as much as possible.
203
204 "make allmodconfig"
205 Create a ./.config file by setting symbol
206 values to 'm' as much as possible.
207
208 "make allnoconfig" Create a ./.config file by setting symbol
209 values to 'n' as much as possible.
210
211 "make randconfig" Create a ./.config file by setting symbol
212 values to random values.
213
214 "make localmodconfig" Create a config based on current config and
215 loaded modules (lsmod). Disables any module
216 option that is not needed for the loaded modules.
217
218 To create a localmodconfig for another machine,
219 store the lsmod of that machine into a file
220 and pass it in as a LSMOD parameter.
221
222 target$ lsmod > /tmp/mylsmod
223 target$ scp /tmp/mylsmod host:/tmp
224
225 host$ make LSMOD=/tmp/mylsmod localmodconfig
226
227 The above also works when cross compiling.
228
229 "make localyesconfig" Similar to localmodconfig, except it will convert
230 all module options to built in (=y) options.
231
232 You can find more information on using the Linux kernel config tools
233 in Documentation/kbuild/kconfig.txt.
234
235 - NOTES on ``make config``:
236
237 - Having unnecessary drivers will make the kernel bigger, and can
238 under some circumstances lead to problems: probing for a
239 nonexistent controller card may confuse your other controllers
240
241 - A kernel with math-emulation compiled in will still use the
242 coprocessor if one is present: the math emulation will just
243 never get used in that case. The kernel will be slightly larger,
244 but will work on different machines regardless of whether they
245 have a math coprocessor or not.
246
247 - The "kernel hacking" configuration details usually result in a
248 bigger or slower kernel (or both), and can even make the kernel
249 less stable by configuring some routines to actively try to
250 break bad code to find kernel problems (kmalloc()). Thus you
251 should probably answer 'n' to the questions for "development",
252 "experimental", or "debugging" features.
253
254Compiling the kernel
255--------------------
256
257 - Make sure you have at least gcc 3.2 available.
258 For more information, refer to :ref:`Documentation/process/changes.rst <changes>`.
259
260 Please note that you can still run a.out user programs with this kernel.
261
262 - Do a ``make`` to create a compressed kernel image. It is also
263 possible to do ``make install`` if you have lilo installed to suit the
264 kernel makefiles, but you may want to check your particular lilo setup first.
265
266 To do the actual install, you have to be root, but none of the normal
267 build should require that. Don't take the name of root in vain.
268
269 - If you configured any of the parts of the kernel as ``modules``, you
270 will also have to do ``make modules_install``.
271
272 - Verbose kernel compile/build output:
273
274 Normally, the kernel build system runs in a fairly quiet mode (but not
275 totally silent). However, sometimes you or other kernel developers need
276 to see compile, link, or other commands exactly as they are executed.
277 For this, use "verbose" build mode. This is done by passing
278 ``V=1`` to the ``make`` command, e.g.::
279
280 make V=1 all
281
282 To have the build system also tell the reason for the rebuild of each
283 target, use ``V=2``. The default is ``V=0``.
284
285 - Keep a backup kernel handy in case something goes wrong. This is
286 especially true for the development releases, since each new release
287 contains new code which has not been debugged. Make sure you keep a
288 backup of the modules corresponding to that kernel, as well. If you
289 are installing a new kernel with the same version number as your
290 working kernel, make a backup of your modules directory before you
291 do a ``make modules_install``.
292
293 Alternatively, before compiling, use the kernel config option
294 "LOCALVERSION" to append a unique suffix to the regular kernel version.
295 LOCALVERSION can be set in the "General Setup" menu.
296
297 - In order to boot your new kernel, you'll need to copy the kernel
298 image (e.g. .../linux/arch/x86/boot/bzImage after compilation)
299 to the place where your regular bootable kernel is found.
300
301 - Booting a kernel directly from a floppy without the assistance of a
302 bootloader such as LILO, is no longer supported.
303
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,
318 reboot, and enjoy!
319
320 If you ever need to change the default root device, video mode,
321 ramdisk size, etc. in the kernel image, use the ``rdev`` program (or
322 alternatively the LILO boot options when appropriate). No need to
323 recompile the kernel to change these parameters.
324
325 - Reboot with the new kernel and enjoy.
326
327If something goes wrong
328-----------------------
329
330 - If you have problems that seem to be due to kernel bugs, please check
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.)
409
410 gdb'ing a non-running kernel currently fails because ``gdb`` (wrongly)
411 disregards the starting offset for which the kernel is compiled.