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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 the8kernel, 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 by14 Linus Torvalds with assistance from a loosely-knit team of hackers across15 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, demand19 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 the23 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 and30 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, and32 ARC architectures.33 34 Linux is easily portable to most general-purpose 32- or 64-bit architectures35 as long as they have a paged memory management unit (PMMU) and a port of the36 GNU C compiler (gcc) (part of The GNU Compiler Collection, GCC). Linux has37 also been ported to a number of architectures without a PMMU, although38 functionality is then obviously somewhat limited.39 Linux has also been ported to itself. You can now run the kernel as a40 userspace application - this is called UserMode Linux (UML).41 42Documentation43-------------44 45 - There is a lot of documentation available both in electronic form on46 the Internet and in books, both Linux-specific and pertaining to47 general UNIX questions. I'd recommend looking into the documentation48 subdirectories on any Linux FTP site for the LDP (Linux Documentation49 Project) books. This README is not meant to be documentation on the50 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 some54 drivers for example. Please read the55 :ref:`Documentation/process/changes.rst <changes>` file, as it56 contains information about the problems, which may result by upgrading57 your kernel.58 59Installing the kernel source60----------------------------61 62 - If you install the full sources, put the kernel tarball in a63 directory where you have permissions (e.g. your home directory) and64 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 (usually71 incomplete) set of kernel headers that are used by the library header72 files. They should match the library, and not get messed up by73 whatever the kernel-du-jour happens to be.74 75 - You can also upgrade between 6.x releases by patching. Patches are76 distributed in the xz format. To install by patching, get all the77 newer patch files, enter the top level directory of the kernel source78 (linux-6.x) and execute::79 80 xz -cd ../patch-6.x.xz | patch -p181 82 Replace "x" for all versions bigger than the version "x" of your current83 source tree, **in_order**, and you should be ok. You may want to remove84 the backup files (some-file-name~ or some-file-name.orig), and make sure85 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 kernels89 (also known as the -stable kernels) are not incremental but instead apply90 directly to the base 6.x kernel. For example, if your base kernel is 6.091 and you want to apply the 6.0.3 patch, you must not first apply the 6.0.192 and 6.0.2 patches. Similarly, if you are running kernel version 6.0.2 and93 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 in95 :ref:`Documentation/process/applying-patches.rst <applying_patches>`.96 97 Alternatively, the script patch-kernel can be used to automate this98 process. It determines the current kernel version and applies any99 patches found::100 101 linux/scripts/patch-kernel linux102 103 The first argument in the command above is the location of the104 kernel source. Patches are applied from the current directory, but105 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 linux110 make mrproper111 112 You should now have the sources correctly installed.113 114Software requirements115---------------------116 117 Compiling and running the 6.x kernels requires up-to-date118 versions of various software packages. Consult119 :ref:`Documentation/process/changes.rst <changes>` for the minimum version numbers120 required and how to get updates for these packages. Beware that using121 excessively old versions of these packages can cause indirect122 errors that are very difficult to track down, so don't assume that123 you can just update packages when obvious problems arise during124 build or operation.125 126Build directory for the kernel127------------------------------128 129 When compiling the kernel, all output files will per default be130 stored together with the kernel source code.131 Using the option ``make O=output/dir`` allows you to specify an alternate132 place for the output files (including .config).133 Example::134 135 kernel source code: /usr/src/linux-6.x136 build directory: /home/name/build/kernel137 138 To configure and build the kernel, use::139 140 cd /usr/src/linux-6.x141 make O=/home/name/build/kernel menuconfig142 make O=/home/name/build/kernel143 sudo make O=/home/name/build/kernel modules_install install144 145 Please note: If the ``O=output/dir`` option is used, then it must be146 used for all invocations of make.147 148Configuring the kernel149----------------------150 151 Do not skip this step even if you are only upgrading one minor152 version. New configuration options are added in each release, and153 odd problems will turn up if the configuration files are not set up154 as expected. If you want to carry your existing configuration to a155 new version with minimal work, use ``make oldconfig``, which will156 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 of171 your existing ./.config file and asking about172 new config symbols.173 174 "make olddefconfig"175 Like above, but sets new symbols to their default176 values without prompting.177 178 "make defconfig" Create a ./.config file by using the default179 symbol values from either arch/$ARCH/defconfig180 or arch/$ARCH/configs/${PLATFORM}_defconfig,181 depending on the architecture.182 183 "make ${PLATFORM}_defconfig"184 Create a ./.config file by using the default185 symbol values from186 arch/$ARCH/configs/${PLATFORM}_defconfig.187 Use "make help" to get a list of all available188 platforms of your architecture.189 190 "make allyesconfig"191 Create a ./.config file by setting symbol192 values to 'y' as much as possible.193 194 "make allmodconfig"195 Create a ./.config file by setting symbol196 values to 'm' as much as possible.197 198 "make allnoconfig" Create a ./.config file by setting symbol199 values to 'n' as much as possible.200 201 "make randconfig" Create a ./.config file by setting symbol202 values to random values.203 204 "make localmodconfig" Create a config based on current config and205 loaded modules (lsmod). Disables any module206 option that is not needed for the loaded modules.207 208 To create a localmodconfig for another machine,209 store the lsmod of that machine into a file210 and pass it in as a LSMOD parameter.211 212 Also, you can preserve modules in certain folders213 or kconfig files by specifying their paths in214 parameter LMC_KEEP.215 216 target$ lsmod > /tmp/mylsmod217 target$ scp /tmp/mylsmod host:/tmp218 219 host$ make LSMOD=/tmp/mylsmod \220 LMC_KEEP="drivers/usb:drivers/gpu:fs" \221 localmodconfig222 223 The above also works when cross compiling.224 225 "make localyesconfig" Similar to localmodconfig, except it will convert226 all module options to built in (=y) options. You can227 also preserve modules by LMC_KEEP.228 229 "make kvm_guest.config" Enable additional options for kvm guest kernel230 support.231 232 "make xen.config" Enable additional options for xen dom0 guest kernel233 support.234 235 "make tinyconfig" Configure the tiniest possible kernel.236 237 You can find more information on using the Linux kernel config tools238 in Documentation/kbuild/kconfig.rst.239 240 - NOTES on ``make config``:241 242 - Having unnecessary drivers will make the kernel bigger, and can243 under some circumstances lead to problems: probing for a244 nonexistent controller card may confuse your other controllers.245 246 - A kernel with math-emulation compiled in will still use the247 coprocessor if one is present: the math emulation will just248 never get used in that case. The kernel will be slightly larger,249 but will work on different machines regardless of whether they250 have a math coprocessor or not.251 252 - The "kernel hacking" configuration details usually result in a253 bigger or slower kernel (or both), and can even make the kernel254 less stable by configuring some routines to actively try to255 break bad code to find kernel problems (kmalloc()). Thus you256 should probably answer 'n' to the questions for "development",257 "experimental", or "debugging" features.258 259Compiling the kernel260--------------------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 do266 ``make install`` if you have lilo installed or if your distribution has an267 install script recognised by the kernel's installer. Most popular268 distributions will have a recognized install script. You may want to269 check your distribution's setup first.270 271 To do the actual install, you have to be root, but none of the normal272 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``, you275 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 not280 totally silent). However, sometimes you or other kernel developers need281 to see compile, link, or other commands exactly as they are executed.282 For this, use "verbose" build mode. This is done by passing283 ``V=1`` to the ``make`` command, e.g.::284 285 make V=1 all286 287 To have the build system also tell the reason for the rebuild of each288 target, use ``V=2``. The default is ``V=0``.289 290 - Keep a backup kernel handy in case something goes wrong. This is291 especially true for the development releases, since each new release292 contains new code which has not been debugged. Make sure you keep a293 backup of the modules corresponding to that kernel, as well. If you294 are installing a new kernel with the same version number as your295 working kernel, make a backup of your modules directory before you296 do a ``make modules_install``.297 298 Alternatively, before compiling, use the kernel config option299 "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 kernel303 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 assistance307 of a bootloader such as LILO or GRUB, is no longer supported in BIOS308 (non-EFI systems). On UEFI/EFI systems, however, you can use EFISTUB309 which allows the motherboard to boot directly to the kernel.310 On modern workstations and desktops, it's generally recommended to use a311 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 in316 active development, though as it was extremely popular, it often comes up317 in documentation. Popular alternatives include GRUB2, rEFInd, Syslinux,318 systemd-boot, or EFISTUB. For various reasons, it's not recommended to use319 software that's no longer in active development.320 321 - Chances are your distribution includes an install script and running322 ``make install`` will be all that's needed. Should that not be the case323 you'll have to identify your bootloader and reference its documentation or324 configure your EFI.325 326Legacy LILO Instructions327------------------------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 or332 /boot/bzImage. To use the new kernel, save a copy of the old image and copy333 the new image over the old one. Then, you MUST RERUN LILO to update the334 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 wish337 to edit /etc/lilo.conf to specify an entry for your old kernel image338 (say, /vmlinux.old) in case the new one does not work. See the LILO docs339 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 the345 kernel image, use your bootloader's boot options where appropriate. No need346 to recompile the kernel to change these parameters.347 348 - Reboot with the new kernel and enjoy.349 350 351If something goes wrong352-----------------------353 354If you have problems that seem to be due to kernel bugs, please follow the355instructions at 'Documentation/admin-guide/reporting-issues.rst'.356 357Hints on understanding kernel bug reports are in358'Documentation/admin-guide/bug-hunting.rst'. More on debugging the kernel359with gdb is in 'Documentation/dev-tools/gdb-kernel-debugging.rst' and360'Documentation/dev-tools/kgdb.rst'.361