| .. _readme: |
| |
| Linux kernel release 5.x <http://kernel.org/> |
| ============================================= |
| |
| These are the release notes for Linux version 5. 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 v2 - 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 Xtensa, and |
| ARC 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. Please read the |
| :ref:`Documentation/process/changes.rst <changes>` file, as it |
| contains information about the problems, which may result by upgrading |
| your kernel. |
| |
| Installing the kernel source |
| ---------------------------- |
| |
| - If you install the full sources, put the kernel tarball in a |
| directory where you have permissions (e.g. your home directory) and |
| unpack it:: |
| |
| xz -cd linux-5.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 5.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-5.x) and execute:: |
| |
| xz -cd ../patch-5.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 5.x kernels, patches for the 5.x.y kernels |
| (also known as the -stable kernels) are not incremental but instead apply |
| directly to the base 5.x kernel. For example, if your base kernel is 5.0 |
| and you want to apply the 5.0.3 patch, you must not first apply the 5.0.1 |
| and 5.0.2 patches. Similarly, if you are running kernel version 5.0.2 and |
| want to jump to 5.0.3, you must first reverse the 5.0.2 patch (that is, |
| patch -R) **before** applying the 5.0.3 patch. You can read more on this in |
| :ref:`Documentation/process/applying-patches.rst <applying_patches>`. |
| |
| 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 5.x kernels requires up-to-date |
| versions of various software packages. Consult |
| :ref:`Documentation/process/changes.rst <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`` allows you to specify an alternate |
| place for the output files (including .config). |
| Example:: |
| |
| kernel source code: /usr/src/linux-5.x |
| build directory: /home/name/build/kernel |
| |
| To configure and build the kernel, use:: |
| |
| cd /usr/src/linux-5.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" Qt based configuration tool. |
| |
| "make gconfig" 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 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/${PLATFORM}_defconfig. |
| Use "make help" to get a list of all available |
| platforms of your architecture. |
| |
| "make allyesconfig" |
| Create a ./.config file by setting symbol |
| values to 'y' as much as possible. |
| |
| "make allmodconfig" |
| Create a ./.config file by setting symbol |
| values to 'm' as much as possible. |
| |
| "make allnoconfig" Create a ./.config file by setting symbol |
| values to 'n' as much as possible. |
| |
| "make randconfig" Create a ./.config file by setting symbol |
| values to random values. |
| |
| "make localmodconfig" Create a config based on current config and |
| loaded modules (lsmod). Disables any module |
| option that is not needed for the loaded modules. |
| |
| To create a localmodconfig for another machine, |
| store the lsmod of that machine into a file |
| and pass it in as a LSMOD parameter. |
| |
| Also, you can preserve modules in certain folders |
| or kconfig files by specifying their paths in |
| parameter LMC_KEEP. |
| |
| target$ lsmod > /tmp/mylsmod |
| target$ scp /tmp/mylsmod host:/tmp |
| |
| host$ make LSMOD=/tmp/mylsmod \ |
| LMC_KEEP="drivers/usb:drivers/gpu:fs" \ |
| 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 |
| also preserve modules by LMC_KEEP. |
| |
| "make kvm_guest.config" Enable additional options for kvm guest kernel |
| support. |
| |
| "make xen.config" Enable additional options for xen dom0 guest kernel |
| support. |
| |
| "make tinyconfig" Configure the tiniest possible kernel. |
| |
| You can find more information on using the Linux kernel config tools |
| in Documentation/kbuild/kconfig.rst. |
| |
| - 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. |
| |
| - 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 4.9 available. |
| For more information, refer to :ref:`Documentation/process/changes.rst <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 passing |
| ``V=1`` to 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/x86/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, |
| etc. in the kernel image, use your bootloader's boot options |
| where 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/admin-guide/bug-hunting.rst |
| |
| - 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 |
| https://www.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 |
| 'Documentation/admin-guide/reporting-issues.rst' 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/x86/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. |
