diff options
author | Linus Torvalds <torvalds@linux-foundation.org> | 2016-12-12 21:58:13 -0800 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2016-12-12 21:58:13 -0800 |
commit | e7aa8c2eb11ba69b1b69099c3c7bd6be3087b0ba (patch) | |
tree | f63906f41699c8e38af9d12b063e2ceab0286ef2 /Documentation/admin-guide | |
parent | e34bac726d27056081d0250c0e173e4b155aa340 (diff) | |
parent | 868c97a846a73e937d835b09b8c885a69df50ec8 (diff) |
Merge tag 'docs-4.10' of git://git.lwn.net/linux
Pull documentation update from Jonathan Corbet:
"These are the documentation changes for 4.10.
It's another busy cycle for the docs tree, as the sphinx conversion
continues. Highlights include:
- Further work on PDF output, which remains a bit of a pain but
should be more solid now.
- Five more DocBook template files converted to Sphinx. Only 27 to
go... Lots of plain-text files have also been converted and
integrated.
- Images in binary formats have been replaced with more
source-friendly versions.
- Various bits of organizational work, including the renaming of
various files discussed at the kernel summit.
- New documentation for the device_link mechanism.
... and, of course, lots of typo fixes and small updates"
* tag 'docs-4.10' of git://git.lwn.net/linux: (193 commits)
dma-buf: Extract dma-buf.rst
Update Documentation/00-INDEX
docs: 00-INDEX: document directories/files with no docs
docs: 00-INDEX: remove non-existing entries
docs: 00-INDEX: add missing entries for documentation files/dirs
docs: 00-INDEX: consolidate process/ and admin-guide/ description
scripts: add a script to check if Documentation/00-INDEX is sane
Docs: change sh -> awk in REPORTING-BUGS
Documentation/core-api/device_link: Add initial documentation
core-api: remove an unexpected unident
ppc/idle: Add documentation for powersave=off
Doc: Correct typo, "Introdution" => "Introduction"
Documentation/atomic_ops.txt: convert to ReST markup
Documentation/local_ops.txt: convert to ReST markup
Documentation/assoc_array.txt: convert to ReST markup
docs-rst: parse-headers.pl: cleanup the documentation
docs-rst: fix media cleandocs target
docs-rst: media/Makefile: reorganize the rules
docs-rst: media: build SVG from graphviz files
docs-rst: replace bayer.png by a SVG image
...
Diffstat (limited to 'Documentation/admin-guide')
28 files changed, 12921 insertions, 0 deletions
diff --git a/Documentation/admin-guide/README.rst b/Documentation/admin-guide/README.rst new file mode 100644 index 000000000000..1b6dfb2b3adb --- /dev/null +++ b/Documentation/admin-guide/README.rst @@ -0,0 +1,411 @@ +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, ARC 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 + :ref:`Documentation/process/changes.rst <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 (e.g. 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 + :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 4.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-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" 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 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 + + - 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 :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, + 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/admin-guide/oops-tracing.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 + 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 :ref:`admin-guide/reporting-bugs.rst <reportingbugs>` + 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/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. diff --git a/Documentation/admin-guide/binfmt-misc.rst b/Documentation/admin-guide/binfmt-misc.rst new file mode 100644 index 000000000000..97b0d7927078 --- /dev/null +++ b/Documentation/admin-guide/binfmt-misc.rst @@ -0,0 +1,151 @@ +Kernel Support for miscellaneous (your favourite) Binary Formats v1.1 +===================================================================== + +This Kernel feature allows you to invoke almost (for restrictions see below) +every program by simply typing its name in the shell. +This includes for example compiled Java(TM), Python or Emacs programs. + +To achieve this you must tell binfmt_misc which interpreter has to be invoked +with which binary. Binfmt_misc recognises the binary-type by matching some bytes +at the beginning of the file with a magic byte sequence (masking out specified +bits) you have supplied. Binfmt_misc can also recognise a filename extension +aka ``.com`` or ``.exe``. + +First you must mount binfmt_misc:: + + mount binfmt_misc -t binfmt_misc /proc/sys/fs/binfmt_misc + +To actually register a new binary type, you have to set up a string looking like +``:name:type:offset:magic:mask:interpreter:flags`` (where you can choose the +``:`` upon your needs) and echo it to ``/proc/sys/fs/binfmt_misc/register``. + +Here is what the fields mean: + +- ``name`` + is an identifier string. A new /proc file will be created with this + ``name below /proc/sys/fs/binfmt_misc``; cannot contain slashes ``/`` for + obvious reasons. +- ``type`` + is the type of recognition. Give ``M`` for magic and ``E`` for extension. +- ``offset`` + is the offset of the magic/mask in the file, counted in bytes. This + defaults to 0 if you omit it (i.e. you write ``:name:type::magic...``). + Ignored when using filename extension matching. +- ``magic`` + is the byte sequence binfmt_misc is matching for. The magic string + may contain hex-encoded characters like ``\x0a`` or ``\xA4``. Note that you + must escape any NUL bytes; parsing halts at the first one. In a shell + environment you might have to write ``\\x0a`` to prevent the shell from + eating your ``\``. + If you chose filename extension matching, this is the extension to be + recognised (without the ``.``, the ``\x0a`` specials are not allowed). + Extension matching is case sensitive, and slashes ``/`` are not allowed! +- ``mask`` + is an (optional, defaults to all 0xff) mask. You can mask out some + bits from matching by supplying a string like magic and as long as magic. + The mask is anded with the byte sequence of the file. Note that you must + escape any NUL bytes; parsing halts at the first one. Ignored when using + filename extension matching. +- ``interpreter`` + is the program that should be invoked with the binary as first + argument (specify the full path) +- ``flags`` + is an optional field that controls several aspects of the invocation + of the interpreter. It is a string of capital letters, each controls a + certain aspect. The following flags are supported: + + ``P`` - preserve-argv[0] + Legacy behavior of binfmt_misc is to overwrite + the original argv[0] with the full path to the binary. When this + flag is included, binfmt_misc will add an argument to the argument + vector for this purpose, thus preserving the original ``argv[0]``. + e.g. If your interp is set to ``/bin/foo`` and you run ``blah`` + (which is in ``/usr/local/bin``), then the kernel will execute + ``/bin/foo`` with ``argv[]`` set to ``["/bin/foo", "/usr/local/bin/blah", "blah"]``. The interp has to be aware of this so it can + execute ``/usr/local/bin/blah`` + with ``argv[]`` set to ``["blah"]``. + ``O`` - open-binary + Legacy behavior of binfmt_misc is to pass the full path + of the binary to the interpreter as an argument. When this flag is + included, binfmt_misc will open the file for reading and pass its + descriptor as an argument, instead of the full path, thus allowing + the interpreter to execute non-readable binaries. This feature + should be used with care - the interpreter has to be trusted not to + emit the contents of the non-readable binary. + ``C`` - credentials + Currently, the behavior of binfmt_misc is to calculate + the credentials and security token of the new process according to + the interpreter. When this flag is included, these attributes are + calculated according to the binary. It also implies the ``O`` flag. + This feature should be used with care as the interpreter + will run with root permissions when a setuid binary owned by root + is run with binfmt_misc. + ``F`` - fix binary + The usual behaviour of binfmt_misc is to spawn the + binary lazily when the misc format file is invoked. However, + this doesn``t work very well in the face of mount namespaces and + changeroots, so the ``F`` mode opens the binary as soon as the + emulation is installed and uses the opened image to spawn the + emulator, meaning it is always available once installed, + regardless of how the environment changes. + + +There are some restrictions: + + - the whole register string may not exceed 1920 characters + - the magic must reside in the first 128 bytes of the file, i.e. + offset+size(magic) has to be less than 128 + - the interpreter string may not exceed 127 characters + +To use binfmt_misc you have to mount it first. You can mount it with +``mount -t binfmt_misc none /proc/sys/fs/binfmt_misc`` command, or you can add +a line ``none /proc/sys/fs/binfmt_misc binfmt_misc defaults 0 0`` to your +``/etc/fstab`` so it auto mounts on boot. + +You may want to add the binary formats in one of your ``/etc/rc`` scripts during +boot-up. Read the manual of your init program to figure out how to do this +right. + +Think about the order of adding entries! Later added entries are matched first! + + +A few examples (assumed you are in ``/proc/sys/fs/binfmt_misc``): + +- enable support for em86 (like binfmt_em86, for Alpha AXP only):: + + echo ':i386:M::\x7fELF\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x03:\xff\xff\xff\xff\xff\xfe\xfe\xff\xff\xff\xff\xff\xff\xff\xff\xff\xfb\xff\xff:/bin/em86:' > register + echo ':i486:M::\x7fELF\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x06:\xff\xff\xff\xff\xff\xfe\xfe\xff\xff\xff\xff\xff\xff\xff\xff\xff\xfb\xff\xff:/bin/em86:' > register + +- enable support for packed DOS applications (pre-configured dosemu hdimages):: + + echo ':DEXE:M::\x0eDEX::/usr/bin/dosexec:' > register + +- enable support for Windows executables using wine:: + + echo ':DOSWin:M::MZ::/usr/local/bin/wine:' > register + +For java support see Documentation/admin-guide/java.rst + + +You can enable/disable binfmt_misc or one binary type by echoing 0 (to disable) +or 1 (to enable) to ``/proc/sys/fs/binfmt_misc/status`` or +``/proc/.../the_name``. +Catting the file tells you the current status of ``binfmt_misc/the_entry``. + +You can remove one entry or all entries by echoing -1 to ``/proc/.../the_name`` +or ``/proc/sys/fs/binfmt_misc/status``. + + +Hints +----- + +If you want to pass special arguments to your interpreter, you can +write a wrapper script for it. See Documentation/admin-guide/java.rst for an +example. + +Your interpreter should NOT look in the PATH for the filename; the kernel +passes it the full filename (or the file descriptor) to use. Using ``$PATH`` can +cause unexpected behaviour and can be a security hazard. + + +Richard Günther <rguenth@tat.physik.uni-tuebingen.de> diff --git a/Documentation/admin-guide/braille-console.rst b/Documentation/admin-guide/braille-console.rst new file mode 100644 index 000000000000..18e79337dcfd --- /dev/null +++ b/Documentation/admin-guide/braille-console.rst @@ -0,0 +1,38 @@ +Linux Braille Console +===================== + +To get early boot messages on a braille device (before userspace screen +readers can start), you first need to compile the support for the usual serial +console (see :ref:`Documentation/admin-guide/serial-console.rst <serial_console>`), and +for braille device +(in :menuselection:`Device Drivers --> Accessibility support --> Console on braille device`). + +Then you need to specify a ``console=brl``, option on the kernel command line, the +format is:: + + console=brl,serial_options... + +where ``serial_options...`` are the same as described in +:ref:`Documentation/admin-guide/serial-console.rst <serial_console>`. + +So for instance you can use ``console=brl,ttyS0`` if the braille device is connected to the first serial port, and ``console=brl,ttyS0,115200`` to +override the baud rate to 115200, etc. + +By default, the braille device will just show the last kernel message (console +mode). To review previous messages, press the Insert key to switch to the VT +review mode. In review mode, the arrow keys permit to browse in the VT content, +:kbd:`PAGE-UP`/:kbd:`PAGE-DOWN` keys go at the top/bottom of the screen, and +the :kbd:`HOME` key goes back +to the cursor, hence providing very basic screen reviewing facility. + +Sound feedback can be obtained by adding the ``braille_console.sound=1`` kernel +parameter. + +For simplicity, only one braille console can be enabled, other uses of +``console=brl,...`` will be discarded. Also note that it does not interfere with +the console selection mechanism described in +:ref:`Documentation/admin-guide/serial-console.rst <serial_console>`. + +For now, only the VisioBraille device is supported. + +Samuel Thibault <samuel.thibault@ens-lyon.org> diff --git a/Documentation/admin-guide/bug-bisect.rst b/Documentation/admin-guide/bug-bisect.rst new file mode 100644 index 000000000000..59567da344e8 --- /dev/null +++ b/Documentation/admin-guide/bug-bisect.rst @@ -0,0 +1,76 @@ +Bisecting a bug ++++++++++++++++ + +Last updated: 28 October 2016 + +Introduction +============ + +Always try the latest kernel from kernel.org and build from source. If you are +not confident in doing that please report the bug to your distribution vendor +instead of to a kernel developer. + +Finding bugs is not always easy. Have a go though. If you can't find it don't +give up. Report as much as you have found to the relevant maintainer. See +MAINTAINERS for who that is for the subsystem you have worked on. + +Before you submit a bug report read +:ref:`Documentation/admin-guide/reporting-bugs.rst <reportingbugs>`. + +Devices not appearing +===================== + +Often this is caused by udev/systemd. Check that first before blaming it +on the kernel. + +Finding patch that caused a bug |