Linux

    Linux kernel release 3.x <http://kernel.org/>

These are the release notes for Linux version 3. 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:

  gzip -cd linux-3.X.tar.gz | tar xvf -

  or

  bzip2 -dc linux-3.X.tar.bz2 | 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 3.x releases by patching. Patches are distributed in the traditional gzip and the newer bzip2 format. To install by patching, get all the newer patch files, enter the top level directory of the kernel source (linux-3.X) and execute:

  gzip -cd ../patch-3.x.gz | patch -p1

  or

  bzip2 -dc ../patch-3.x.bz2 | 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 3.x kernels, patches for the 3.x.y kernels (also known as the -stable kernels) are not incremental but instead apply directly to the base 3.x kernel. For example, if your base kernel is 3.0 and you want to apply the 3.0.3 patch, you must not first apply the 3.0.1 and 3.0.2 patches. Similarly, if you are running kernel version 3.0.2 and want to jump to 3.0.3, you must first reverse the 3.0.2 patch (that is, patch -R) before applying the 3.0.3 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 3.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-3.X
 build directory:    /home/name/build/kernel

To configure and build the kernel, use:

 cd /usr/src/linux-3.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.