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Linux kernel release 4.x <http://kernel.org/>

These are the release notes for Linux version 4. Read them carefully,

as they tell you what this is all about, explain how to install the

kernel, and what to do if something goes wrong.

WHAT IS LINUX?

Linux is a clone of the operating system Unix, written from scratch by

Linus Torvalds with assistance from a loosely-knit team of hackers across

the Net. It aims towards POSIX and Single UNIX Specification compliance.

It has all the features you would expect in a modern fully-fledged Unix,

including true multitasking, virtual memory, shared libraries, demand

loading, shared copy-on-write executables, proper memory management,

and multistack networking including IPv4 and IPv6.

It is distributed under the GNU General Public License - see the

accompanying COPYING file for more details.

ON WHAT HARDWARE DOES IT RUN?

Although originally developed first for 32-bit x86-based PCs (386 or higher),

today Linux also runs on (at least) the Compaq Alpha AXP, Sun SPARC and

UltraSPARC, Motorola 68000, PowerPC, PowerPC64, ARM, Hitachi SuperH, Cell,

IBM S/390, MIPS, HP PA-RISC, Intel IA-64, DEC VAX, AMD x86-64, AXIS CRIS,

Xtensa, Tilera TILE, AVR32 and Renesas M32R architectures.

Linux is easily portable to most general-purpose 32- or 64-bit architectures

as long as they have a paged memory management unit (PMMU) and a port of the

GNU C compiler (gcc) (part of The GNU Compiler Collection, GCC). Linux has

also been ported to a number of architectures without a PMMU, although

functionality is then obviously somewhat limited.

Linux has also been ported to itself. You can now run the kernel as a

userspace application - this is called UserMode Linux (UML).

DOCUMENTATION:

- There is a lot of documentation available both in electronic form on

the Internet and in books, both Linux-specific and pertaining to

general UNIX questions. I'd recommend looking into the documentation

subdirectories on any Linux FTP site for the LDP (Linux Documentation

Project) books. This README is not meant to be documentation on the

system: there are much better sources available.

- There are various README files in the Documentation/ subdirectory:

these typically contain kernel-specific installation notes for some

drivers for example. See Documentation/00-INDEX for a list of what

is contained in each file. Please read the Changes file, as it

contains information about the problems, which may result by upgrading

your kernel.

- The Documentation/DocBook/ subdirectory contains several guides for

kernel developers and users. These guides can be rendered in a

number of formats: PostScript (.ps), PDF, HTML, & man-pages, among others.

After installation, "make psdocs", "make pdfdocs", "make htmldocs",

or "make mandocs" will render the documentation in the requested format.

INSTALLING the kernel source:

- If you install the full sources, put the kernel tarball in a

directory where you have permissions (eg. your home directory) and

unpack it:

xz -cd linux-4.X.tar.xz | tar xvf -

Replace "X" with the version number of the latest kernel.

Do NOT use the /usr/src/linux area! This area has a (usually

incomplete) set of kernel headers that are used by the library header

files. They should match the library, and not get messed up by

whatever the kernel-du-jour happens to be.

- You can also upgrade between 4.x releases by patching. Patches are

distributed in the xz format. To install by patching, get all the

newer patch files, enter the top level directory of the kernel source

(linux-4.X) and execute:

xz -cd ../patch-4.x.xz | patch -p1

Replace "x" for all versions bigger than the version "X" of your current

source tree, _in_order_, and you should be ok. You may want to remove

the backup files (some-file-name~ or some-file-name.orig), and make sure

that there are no failed patches (some-file-name# or some-file-name.rej).

If there are, either you or I have made a mistake.

Unlike patches for the 4.x kernels, patches for the 4.x.y kernels

(also known as the -stable kernels) are not incremental but instead apply

directly to the base 4.x kernel. For example, if your base kernel is 4.0

and you want to apply the 4.0.3 patch, you must not first apply the 4.0.1

and 4.0.2 patches. Similarly, if you are running kernel version 4.0.2 and

want to jump to 4.0.3, you must first reverse the 4.0.2 patch (that is,

patch -R) _before_ applying the 4.0.3 patch. You can read more on this in

Documentation/applying-patches.txt

Alternatively, the script patch-kernel can be used to automate this

process. It determines the current kernel version and applies any

patches found.

linux/scripts/patch-kernel linux

The first argument in the command above is the location of the

kernel source. Patches are applied from the current directory, but

an alternative directory can be specified as the second argument.

- Make sure you have no stale .o files and dependencies lying around:

cd linux

make mrproper

You should now have the sources correctly installed.

SOFTWARE REQUIREMENTS

Compiling and running the 4.x kernels requires up-to-date

versions of various software packages. Consult

Documentation/Changes for the minimum version numbers required

and how to get updates for these packages. Beware that using

excessively old versions of these packages can cause indirect

errors that are very difficult to track down, so don't assume that

you can just update packages when obvious problems arise during

build or operation.

BUILD directory for the kernel:

When compiling the kernel, all output files will per default be

stored together with the kernel source code.

Using the option "make O=output/dir" allow you to specify an alternate

place for the output files (including .config).

Example:

kernel source code: /usr/src/linux-4.X

build directory: /home/name/build/kernel

To configure and build the kernel, use:

cd /usr/src/linux-4.X

make O=/home/name/build/kernel menuconfig

make O=/home/name/build/kernel

sudo make O=/home/name/build/kernel modules_install install

Please note: If the 'O=output/dir' option is used, then it must be

used for all invocations of make.

CONFIGURING the kernel:

Do not skip this step even if you are only upgrading one minor

version. New configuration options are added in each release, and

odd problems will turn up if the configuration files are not set up

as expected. If you want to carry your existing configuration to a

new version with minimal work, use "make oldconfig", which will

only ask you for the answers to new questions.

- Alternative configuration commands are:

"make config" Plain text interface.

"make menuconfig" Text based color menus, radiolists & dialogs.

"make nconfig" Enhanced text based color menus.

"make xconfig" X windows (Qt) based configuration tool.

"make gconfig" X windows (GTK+) based configuration tool.

"make oldconfig" Default all questions based on the contents of

your existing ./.config file and asking about

new config symbols.

"make silentoldconfig"

Like above, but avoids cluttering the screen

with questions already answered.

Additionally updates the dependencies.

"make olddefconfig"

Like above, but sets new symbols to their default

values without prompting.

"make defconfig" Create a ./.config file by using the default

symbol values from either arch/$ARCH/defconfig

or arch/$ARCH/configs/${PLATFORM}_defconfig,

depending on the architecture.

"make ${PLATFORM}_defconfig"

Create a ./.config file by using the default

symbol values from

arch/$ARCH/configs/${PLATFORM}_defconfig.

Use "make help" to get a list of all available

platforms of your architecture.

"make allyesconfig"

Create a ./.config file by setting symbol

values to 'y' as much as possible.

"make allmodconfig"

Create a ./.config file by setting symbol

values to 'm' as much as possible.

"make allnoconfig" Create a ./.config file by setting symbol

values to 'n' as much as possible.

"make randconfig" Create a ./.config file by setting symbol

values to random values.

"make localmodconfig" Create a config based on current config and

loaded modules (lsmod). Disables any module

option that is not needed for the loaded modules.

To create a localmodconfig for another machine,

store the lsmod of that machine into a file

and pass it in as a LSMOD parameter.

target$ lsmod > /tmp/mylsmod

target$ scp /tmp/mylsmod host:/tmp

host$ make LSMOD=/tmp/mylsmod localmodconfig

The above also works when cross compiling.

"make localyesconfig" Similar to localmodconfig, except it will convert

all module options to built in (=y) options.

You can find more information on using the Linux kernel config tools

in Documentation/kbuild/kconfig.txt.

- NOTES on "make config":

- Having unnecessary drivers will make the kernel bigger, and can

under some circumstances lead to problems: probing for a

nonexistent controller card may confuse your other controllers

- Compiling the kernel with "Processor type" set higher than 386

will result in a kernel that does NOT work on a 386. The

kernel will detect this on bootup, and give up.

- A kernel with math-emulation compiled in will still use the

coprocessor if one is present: the math emulation will just

never get used in that case. The kernel will be slightly larger,

but will work on different machines regardless of whether they

have a math coprocessor or not.

- The "kernel hacking" configuration details usually result in a

bigger or slower kernel (or both), and can even make the kernel

less stable by configuring some routines to actively try to

break bad code to find kernel problems (kmalloc()). Thus you

should probably answer 'n' to the questions for "development",

"experimental", or "debugging" features.

COMPILING the kernel:

- Make sure you have at least gcc 3.2 available.

For more information, refer to Documentation/Changes.

Please note that you can still run a.out user programs with this kernel.

- Do a "make" to create a compressed kernel image. It is also

possible to do "make install" if you have lilo installed to suit the

kernel makefiles, but you may want to check your particular lilo setup first.

To do the actual install, you have to be root, but none of the normal

build should require that. Don't take the name of root in vain.

- If you configured any of the parts of the kernel as `modules', you

will also have to do "make modules_install".

- Verbose kernel compile/build output:

Normally, the kernel build system runs in a fairly quiet mode (but not

totally silent). However, sometimes you or other kernel developers need

to see compile, link, or other commands exactly as they are executed.

For this, use "verbose" build mode. This is done by inserting

"V=1" in the "make" command. E.g.:

make V=1 all

To have the build system also tell the reason for the rebuild of each

target, use "V=2". The default is "V=0".

- Keep a backup kernel handy in case something goes wrong. This is

especially true for the development releases, since each new release

contains new code which has not been debugged. Make sure you keep a

backup of the modules corresponding to that kernel, as well. If you

are installing a new kernel with the same version number as your

working kernel, make a backup of your modules directory before you

do a "make modules_install".

Alternatively, before compiling, use the kernel config option

"LOCALVERSION" to append a unique suffix to the regular kernel version.

LOCALVERSION can be set in the "General Setup" menu.

- In order to boot your new kernel, you'll need to copy the kernel

image (e.g. .../linux/arch/i386/boot/bzImage after compilation)

to the place where your regular bootable kernel is found.

- Booting a kernel directly from a floppy without the assistance of a

bootloader such as LILO, is no longer supported.

If you boot Linux from the hard drive, chances are you use LILO, which

uses the kernel image as specified in the file /etc/lilo.conf. The

kernel image file is usually /vmlinuz, /boot/vmlinuz, /bzImage or

/boot/bzImage. To use the new kernel, save a copy of the old image

and copy the new image over the old one. Then, you MUST RERUN LILO

to update the loading map!! If you don't, you won't be able to boot

the new kernel image.

Reinstalling LILO is usually a matter of running /sbin/lilo.

You may wish to edit /etc/lilo.conf to specify an entry for your

old kernel image (say, /vmlinux.old) in case the new one does not

work. See the LILO docs for more information.

After reinstalling LILO, you should be all set. Shutdown the system,

reboot, and enjoy!

If you ever need to change the default root device, video mode,

ramdisk size, etc. in the kernel image, use the 'rdev' program (or

alternatively the LILO boot options when appropriate). No need to

recompile the kernel to change these parameters.

- Reboot with the new kernel and enjoy.

IF SOMETHING GOES WRONG:

- If you have problems that seem to be due to kernel bugs, please check

the file MAINTAINERS to see if there is a particular person associated

with the part of the kernel that you are having trouble with. If there

isn't anyone listed there, then the second best thing is to mail

them to me (torvalds@linux-foundation.org), and possibly to any other

relevant mailing-list or to the newsgroup.

- In all bug-reports, *please* tell what kernel you are talking about,

how to duplicate the problem, and what your setup is (use your common

sense). If the problem is new, tell me so, and if the problem is

old, please try to tell me when you first noticed it.

- If the bug results in a message like

unable to handle kernel paging request at address C0000010

Oops: 0002

EIP: 0010:XXXXXXXX

eax: xxxxxxxx ebx: xxxxxxxx ecx: xxxxxxxx edx: xxxxxxxx

esi: xxxxxxxx edi: xxxxxxxx ebp: xxxxxxxx

ds: xxxx es: xxxx fs: xxxx gs: xxxx

Pid: xx, process nr: xx

xx xx xx xx xx xx xx xx xx xx

or similar kernel debugging information on your screen or in your

system log, please duplicate it *exactly*. The dump may look

incomprehensible to you, but it does contain information that may

help debugging the problem. The text above the dump is also

important: it tells something about why the kernel dumped code (in

the above example, it's due to a bad kernel pointer). More information

on making sense of the dump is in Documentation/oops-tracing.txt

- If you compiled the kernel with CONFIG_KALLSYMS you can send the dump

as is, otherwise you will have to use the "ksymoops" program to make

sense of the dump (but compiling with CONFIG_KALLSYMS is usually preferred).

This utility can be downloaded from

ftp://ftp.<country>.kernel.org/pub/linux/utils/kernel/ksymoops/ .

Alternatively, you can do the dump lookup by hand:

- In debugging dumps like the above, it helps enormously if you can

look up what the EIP value means. The hex value as such doesn't help

me or anybody else very much: it will depend on your particular

kernel setup. What you should do is take the hex value from the EIP

line (ignore the "0010:"), and look it up in the kernel namelist to

see which kernel function contains the offending address.

To find out the kernel function name, you'll need to find the system

binary associated with the kernel that exhibited the symptom. This is

the file 'linux/vmlinux'. To extract the namelist and match it against

the EIP from the kernel crash, do:

nm vmlinux | sort | less

This will give you a list of kernel addresses sorted in ascending

order, from which it is simple to find the function that contains the

offending address. Note that the address given by the kernel

debugging messages will not necessarily match exactly with the

function addresses (in fact, that is very unlikely), so you can't

just 'grep' the list: the list will, however, give you the starting

point of each kernel function, so by looking for the function that

has a starting address lower than the one you are searching for but

is followed by a function with a higher address you will find the one

you want. In fact, it may be a good idea to include a bit of

"context" in your problem report, giving a few lines around the

interesting one.

If you for some reason cannot do the above (you have a pre-compiled

kernel image or similar), telling me as much about your setup as

possible will help. Please read the REPORTING-BUGS document for details.

- Alternatively, you can use gdb on a running kernel. (read-only; i.e. you

cannot change values or set break points.) To do this, first compile the

kernel with -g; edit arch/i386/Makefile appropriately, then do a "make

clean". You'll also need to enable CONFIG_PROC_FS (via "make config").

After you've rebooted with the new kernel, do "gdb vmlinux /proc/kcore".

You can now use all the usual gdb commands. The command to look up the

point where your system crashed is "l *0xXXXXXXXX". (Replace the XXXes

with the EIP value.)

gdb'ing a non-running kernel currently fails because gdb (wrongly)

disregards the starting offset for which the kernel is compiled.

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