xref: /linux/README (revision bbb20089a3275a19e475dbc21320c3742e3ca423)
1 	Linux kernel release 2.6.xx <http://kernel.org/>
2 
3 These are the release notes for Linux version 2.6.  Read them carefully,
4 as they tell you what this is all about, explain how to install the
5 kernel, and what to do if something goes wrong.
6 
7 WHAT IS LINUX?
8 
9   Linux is a clone of the operating system Unix, written from scratch by
10   Linus Torvalds with assistance from a loosely-knit team of hackers across
11   the Net. It aims towards POSIX and Single UNIX Specification compliance.
12 
13   It has all the features you would expect in a modern fully-fledged Unix,
14   including true multitasking, virtual memory, shared libraries, demand
15   loading, shared copy-on-write executables, proper memory management,
16   and multistack networking including IPv4 and IPv6.
17 
18   It is distributed under the GNU General Public License - see the
19   accompanying COPYING file for more details.
20 
21 ON WHAT HARDWARE DOES IT RUN?
22 
23   Although originally developed first for 32-bit x86-based PCs (386 or higher),
24   today Linux also runs on (at least) the Compaq Alpha AXP, Sun SPARC and
25   UltraSPARC, Motorola 68000, PowerPC, PowerPC64, ARM, Hitachi SuperH, Cell,
26   IBM S/390, MIPS, HP PA-RISC, Intel IA-64, DEC VAX, AMD x86-64, AXIS CRIS,
27   Xtensa, AVR32 and Renesas M32R architectures.
28 
29   Linux is easily portable to most general-purpose 32- or 64-bit architectures
30   as long as they have a paged memory management unit (PMMU) and a port of the
31   GNU C compiler (gcc) (part of The GNU Compiler Collection, GCC). Linux has
32   also been ported to a number of architectures without a PMMU, although
33   functionality is then obviously somewhat limited.
34   Linux has also been ported to itself. You can now run the kernel as a
35   userspace application - this is called UserMode Linux (UML).
36 
37 DOCUMENTATION:
38 
39  - There is a lot of documentation available both in electronic form on
40    the Internet and in books, both Linux-specific and pertaining to
41    general UNIX questions.  I'd recommend looking into the documentation
42    subdirectories on any Linux FTP site for the LDP (Linux Documentation
43    Project) books.  This README is not meant to be documentation on the
44    system: there are much better sources available.
45 
46  - There are various README files in the Documentation/ subdirectory:
47    these typically contain kernel-specific installation notes for some
48    drivers for example. See Documentation/00-INDEX for a list of what
49    is contained in each file.  Please read the Changes file, as it
50    contains information about the problems, which may result by upgrading
51    your kernel.
52 
53  - The Documentation/DocBook/ subdirectory contains several guides for
54    kernel developers and users.  These guides can be rendered in a
55    number of formats:  PostScript (.ps), PDF, HTML, & man-pages, among others.
56    After installation, "make psdocs", "make pdfdocs", "make htmldocs",
57    or "make mandocs" will render the documentation in the requested format.
58 
59 INSTALLING the kernel source:
60 
61  - If you install the full sources, put the kernel tarball in a
62    directory where you have permissions (eg. your home directory) and
63    unpack it:
64 
65 		gzip -cd linux-2.6.XX.tar.gz | tar xvf -
66 
67    or
68 		bzip2 -dc linux-2.6.XX.tar.bz2 | tar xvf -
69 
70 
71    Replace "XX" with the version number of the latest kernel.
72 
73    Do NOT use the /usr/src/linux area! This area has a (usually
74    incomplete) set of kernel headers that are used by the library header
75    files.  They should match the library, and not get messed up by
76    whatever the kernel-du-jour happens to be.
77 
78  - You can also upgrade between 2.6.xx releases by patching.  Patches are
79    distributed in the traditional gzip and the newer bzip2 format.  To
80    install by patching, get all the newer patch files, enter the
81    top level directory of the kernel source (linux-2.6.xx) and execute:
82 
83 		gzip -cd ../patch-2.6.xx.gz | patch -p1
84 
85    or
86 		bzip2 -dc ../patch-2.6.xx.bz2 | patch -p1
87 
88    (repeat xx for all versions bigger than the version of your current
89    source tree, _in_order_) and you should be ok.  You may want to remove
90    the backup files (xxx~ or xxx.orig), and make sure that there are no
91    failed patches (xxx# or xxx.rej). If there are, either you or me has
92    made a mistake.
93 
94    Unlike patches for the 2.6.x kernels, patches for the 2.6.x.y kernels
95    (also known as the -stable kernels) are not incremental but instead apply
96    directly to the base 2.6.x kernel.  Please read
97    Documentation/applying-patches.txt for more information.
98 
99    Alternatively, the script patch-kernel can be used to automate this
100    process.  It determines the current kernel version and applies any
101    patches found.
102 
103 		linux/scripts/patch-kernel linux
104 
105    The first argument in the command above is the location of the
106    kernel source.  Patches are applied from the current directory, but
107    an alternative directory can be specified as the second argument.
108 
109  - If you are upgrading between releases using the stable series patches
110    (for example, patch-2.6.xx.y), note that these "dot-releases" are
111    not incremental and must be applied to the 2.6.xx base tree. For
112    example, if your base kernel is 2.6.12 and you want to apply the
113    2.6.12.3 patch, you do not and indeed must not first apply the
114    2.6.12.1 and 2.6.12.2 patches. Similarly, if you are running kernel
115    version 2.6.12.2 and want to jump to 2.6.12.3, you must first
116    reverse the 2.6.12.2 patch (that is, patch -R) _before_ applying
117    the 2.6.12.3 patch.
118    You can read more on this in Documentation/applying-patches.txt
119 
120  - Make sure you have no stale .o files and dependencies lying around:
121 
122 		cd linux
123 		make mrproper
124 
125    You should now have the sources correctly installed.
126 
127 SOFTWARE REQUIREMENTS
128 
129    Compiling and running the 2.6.xx kernels requires up-to-date
130    versions of various software packages.  Consult
131    Documentation/Changes for the minimum version numbers required
132    and how to get updates for these packages.  Beware that using
133    excessively old versions of these packages can cause indirect
134    errors that are very difficult to track down, so don't assume that
135    you can just update packages when obvious problems arise during
136    build or operation.
137 
138 BUILD directory for the kernel:
139 
140    When compiling the kernel all output files will per default be
141    stored together with the kernel source code.
142    Using the option "make O=output/dir" allow you to specify an alternate
143    place for the output files (including .config).
144    Example:
145      kernel source code:	/usr/src/linux-2.6.N
146      build directory:		/home/name/build/kernel
147 
148    To configure and build the kernel use:
149    cd /usr/src/linux-2.6.N
150    make O=/home/name/build/kernel menuconfig
151    make O=/home/name/build/kernel
152    sudo make O=/home/name/build/kernel modules_install install
153 
154    Please note: If the 'O=output/dir' option is used then it must be
155    used for all invocations of make.
156 
157 CONFIGURING the kernel:
158 
159    Do not skip this step even if you are only upgrading one minor
160    version.  New configuration options are added in each release, and
161    odd problems will turn up if the configuration files are not set up
162    as expected.  If you want to carry your existing configuration to a
163    new version with minimal work, use "make oldconfig", which will
164    only ask you for the answers to new questions.
165 
166  - Alternate configuration commands are:
167 	"make config"      Plain text interface.
168 	"make menuconfig"  Text based color menus, radiolists & dialogs.
169 	"make xconfig"     X windows (Qt) based configuration tool.
170 	"make gconfig"     X windows (Gtk) based configuration tool.
171 	"make oldconfig"   Default all questions based on the contents of
172 			   your existing ./.config file and asking about
173 			   new config symbols.
174 	"make silentoldconfig"
175 			   Like above, but avoids cluttering the screen
176 			   with questions already answered.
177 			   Additionally updates the dependencies.
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 	"make ${PLATFORM}_defconfig"
183 			  Create a ./.config file by using the default
184 			  symbol values from
185 			  arch/$ARCH/configs/${PLATFORM}_defconfig.
186 			  Use "make help" to get a list of all available
187 			  platforms of your architecture.
188 	"make allyesconfig"
189 			   Create a ./.config file by setting symbol
190 			   values to 'y' as much as possible.
191 	"make allmodconfig"
192 			   Create a ./.config file by setting symbol
193 			   values to 'm' as much as possible.
194 	"make allnoconfig" Create a ./.config file by setting symbol
195 			   values to 'n' as much as possible.
196 	"make randconfig"  Create a ./.config file by setting symbol
197 			   values to random values.
198 
199    You can find more information on using the Linux kernel config tools
200    in Documentation/kbuild/kconfig.txt.
201 
202 	NOTES on "make config":
203 	- having unnecessary drivers will make the kernel bigger, and can
204 	  under some circumstances lead to problems: probing for a
205 	  nonexistent controller card may confuse your other controllers
206 	- compiling the kernel with "Processor type" set higher than 386
207 	  will result in a kernel that does NOT work on a 386.  The
208 	  kernel will detect this on bootup, and give up.
209 	- A kernel with math-emulation compiled in will still use the
210 	  coprocessor if one is present: the math emulation will just
211 	  never get used in that case.  The kernel will be slightly larger,
212 	  but will work on different machines regardless of whether they
213 	  have a math coprocessor or not.
214 	- the "kernel hacking" configuration details usually result in a
215 	  bigger or slower kernel (or both), and can even make the kernel
216 	  less stable by configuring some routines to actively try to
217 	  break bad code to find kernel problems (kmalloc()).  Thus you
218 	  should probably answer 'n' to the questions for
219           "development", "experimental", or "debugging" features.
220 
221 COMPILING the kernel:
222 
223  - Make sure you have at least gcc 3.2 available.
224    For more information, refer to Documentation/Changes.
225 
226    Please note that you can still run a.out user programs with this kernel.
227 
228  - Do a "make" to create a compressed kernel image. It is also
229    possible to do "make install" if you have lilo installed to suit the
230    kernel makefiles, but you may want to check your particular lilo setup first.
231 
232    To do the actual install you have to be root, but none of the normal
233    build should require that. Don't take the name of root in vain.
234 
235  - If you configured any of the parts of the kernel as `modules', you
236    will also have to do "make modules_install".
237 
238  - Verbose kernel compile/build output:
239 
240    Normally the kernel build system runs in a fairly quiet mode (but not
241    totally silent).  However, sometimes you or other kernel developers need
242    to see compile, link, or other commands exactly as they are executed.
243    For this, use "verbose" build mode.  This is done by inserting
244    "V=1" in the "make" command.  E.g.:
245 
246 	make V=1 all
247 
248    To have the build system also tell the reason for the rebuild of each
249    target, use "V=2".  The default is "V=0".
250 
251  - Keep a backup kernel handy in case something goes wrong.  This is
252    especially true for the development releases, since each new release
253    contains new code which has not been debugged.  Make sure you keep a
254    backup of the modules corresponding to that kernel, as well.  If you
255    are installing a new kernel with the same version number as your
256    working kernel, make a backup of your modules directory before you
257    do a "make modules_install".
258    Alternatively, before compiling, use the kernel config option
259    "LOCALVERSION" to append a unique suffix to the regular kernel version.
260    LOCALVERSION can be set in the "General Setup" menu.
261 
262  - In order to boot your new kernel, you'll need to copy the kernel
263    image (e.g. .../linux/arch/i386/boot/bzImage after compilation)
264    to the place where your regular bootable kernel is found.
265 
266  - Booting a kernel directly from a floppy without the assistance of a
267    bootloader such as LILO, is no longer supported.
268 
269    If you boot Linux from the hard drive, chances are you use LILO which
270    uses the kernel image as specified in the file /etc/lilo.conf.  The
271    kernel image file is usually /vmlinuz, /boot/vmlinuz, /bzImage or
272    /boot/bzImage.  To use the new kernel, save a copy of the old image
273    and copy the new image over the old one.  Then, you MUST RERUN LILO
274    to update the loading map!! If you don't, you won't be able to boot
275    the new kernel image.
276 
277    Reinstalling LILO is usually a matter of running /sbin/lilo.
278    You may wish to edit /etc/lilo.conf to specify an entry for your
279    old kernel image (say, /vmlinux.old) in case the new one does not
280    work.  See the LILO docs for more information.
281 
282    After reinstalling LILO, you should be all set.  Shutdown the system,
283    reboot, and enjoy!
284 
285    If you ever need to change the default root device, video mode,
286    ramdisk size, etc.  in the kernel image, use the 'rdev' program (or
287    alternatively the LILO boot options when appropriate).  No need to
288    recompile the kernel to change these parameters.
289 
290  - Reboot with the new kernel and enjoy.
291 
292 IF SOMETHING GOES WRONG:
293 
294  - If you have problems that seem to be due to kernel bugs, please check
295    the file MAINTAINERS to see if there is a particular person associated
296    with the part of the kernel that you are having trouble with. If there
297    isn't anyone listed there, then the second best thing is to mail
298    them to me (torvalds@linux-foundation.org), and possibly to any other
299    relevant mailing-list or to the newsgroup.
300 
301  - In all bug-reports, *please* tell what kernel you are talking about,
302    how to duplicate the problem, and what your setup is (use your common
303    sense).  If the problem is new, tell me so, and if the problem is
304    old, please try to tell me when you first noticed it.
305 
306  - If the bug results in a message like
307 
308 	unable to handle kernel paging request at address C0000010
309 	Oops: 0002
310 	EIP:   0010:XXXXXXXX
311 	eax: xxxxxxxx   ebx: xxxxxxxx   ecx: xxxxxxxx   edx: xxxxxxxx
312 	esi: xxxxxxxx   edi: xxxxxxxx   ebp: xxxxxxxx
313 	ds: xxxx  es: xxxx  fs: xxxx  gs: xxxx
314 	Pid: xx, process nr: xx
315 	xx xx xx xx xx xx xx xx xx xx
316 
317    or similar kernel debugging information on your screen or in your
318    system log, please duplicate it *exactly*.  The dump may look
319    incomprehensible to you, but it does contain information that may
320    help debugging the problem.  The text above the dump is also
321    important: it tells something about why the kernel dumped code (in
322    the above example it's due to a bad kernel pointer). More information
323    on making sense of the dump is in Documentation/oops-tracing.txt
324 
325  - If you compiled the kernel with CONFIG_KALLSYMS you can send the dump
326    as is, otherwise you will have to use the "ksymoops" program to make
327    sense of the dump (but compiling with CONFIG_KALLSYMS is usually preferred).
328    This utility can be downloaded from
329    ftp://ftp.<country>.kernel.org/pub/linux/utils/kernel/ksymoops/ .
330    Alternately you can do the dump lookup by hand:
331 
332  - In debugging dumps like the above, it helps enormously if you can
333    look up what the EIP value means.  The hex value as such doesn't help
334    me or anybody else very much: it will depend on your particular
335    kernel setup.  What you should do is take the hex value from the EIP
336    line (ignore the "0010:"), and look it up in the kernel namelist to
337    see which kernel function contains the offending address.
338 
339    To find out the kernel function name, you'll need to find the system
340    binary associated with the kernel that exhibited the symptom.  This is
341    the file 'linux/vmlinux'.  To extract the namelist and match it against
342    the EIP from the kernel crash, do:
343 
344 		nm vmlinux | sort | less
345 
346    This will give you a list of kernel addresses sorted in ascending
347    order, from which it is simple to find the function that contains the
348    offending address.  Note that the address given by the kernel
349    debugging messages will not necessarily match exactly with the
350    function addresses (in fact, that is very unlikely), so you can't
351    just 'grep' the list: the list will, however, give you the starting
352    point of each kernel function, so by looking for the function that
353    has a starting address lower than the one you are searching for but
354    is followed by a function with a higher address you will find the one
355    you want.  In fact, it may be a good idea to include a bit of
356    "context" in your problem report, giving a few lines around the
357    interesting one.
358 
359    If you for some reason cannot do the above (you have a pre-compiled
360    kernel image or similar), telling me as much about your setup as
361    possible will help.  Please read the REPORTING-BUGS document for details.
362 
363  - Alternately, you can use gdb on a running kernel. (read-only; i.e. you
364    cannot change values or set break points.) To do this, first compile the
365    kernel with -g; edit arch/i386/Makefile appropriately, then do a "make
366    clean". You'll also need to enable CONFIG_PROC_FS (via "make config").
367 
368    After you've rebooted with the new kernel, do "gdb vmlinux /proc/kcore".
369    You can now use all the usual gdb commands. The command to look up the
370    point where your system crashed is "l *0xXXXXXXXX". (Replace the XXXes
371    with the EIP value.)
372 
373    gdb'ing a non-running kernel currently fails because gdb (wrongly)
374    disregards the starting offset for which the kernel is compiled.
375 
376