  The Linux keyboard and console HOWTO
  Andries Brouwer, aeb@cwi.nl
  v2.13, 2002-10-12

  This note contains some information about the Linux keyboard and con­
  sole, and the use of non-ASCII characters.  It describes Linux 2.0.
  ______________________________________________________________________

  Table of Contents



  1. Useful programs

  2. Keyboard generalities

  3. Console generalities

  4. Resetting your terminal

     4.1 Keyboard hardware reset

  5. Delete and Backspace

     5.1 How to tell Unix what character you want to use to delete the last typed character
        5.1.1 `Getty used to do the right thing with DEL and BS but is broken now?'
        5.1.2 `Login behaves differently at the first and second login attempts?'
     5.2 How to tell Linux what code to generate when a key is pressed
        5.2.1 `How do I get a dvorak keyboard?'
        5.2.2 `Why doesn't the Backspace key generate BackSpace by default?'
     5.3 How to tell X to interchange Delete and Backspace
     5.4 How to tell emacs what to do when it receives a Delete or Backspace
     5.5 How to tell emacs to interchange Delete and Backspace
     5.6 How to tell kermit to interchange Delete and Backspace
     5.7 How to tell xterm to interchange Delete and Backspace
     5.8 How to tell xterm about your favourite tty modes
     5.9 How to tell non-Motif X applications that the Del key deletes forward
     5.10 How to tell xmosaic that the Backspace key generates a DEL
     5.11 A better solution for Motif-using programs, like netscape
     5.12 What about termcap and terminfo?
     5.13 A complete solution

  6. The console character sets

  7. Console switching

     7.1 Changing the number of Virtual Consoles

  8. Ctrl-Alt-Del and other special key combinations

     8.1 Ctrl-Alt-Del (Boot)
     8.2 Other combinations
     8.3 X Combinations
     8.4 Dosemu Combinations
     8.5 Composing symbols
     8.6 The SysRq key
     8.7 Problems

  9. How to get out of raw mode

  10. The keyboard LEDs

  11. The TERM variable

     11.1 Terminfo

  12. How to make other programs work with non-ASCII chars

  13. X

     13.1 What precisely does XFree86-2.1 do when it initializes its keymap?

  14. Unusual keys and keyboards

     14.1 Funkeys

  15. Examples of use of loadkeys and xmodmap

     15.1 `I can use only one finger to type with'
     15.2 Sticky keys under

  16. Changing the video mode

     16.1 Instructions for the use of resizecons

  17. Changing the keyboard repeat rate

  18. Scrolling

  19. Screensaving

  20. Screen dumps

  21. Some properties of the VT100 - application key mode

  22. Hardware incompatibility

  23. Copyright



  ______________________________________________________________________

  1.  Useful programs


  The following packages contain keyboard or console related programs.

  kbd-1.06.tar.gz contains loadkeys, dumpkeys, showkey, setmetamode,
  setleds, setfont, showconsolefont, mapscrn, kbd_mode, kbdrate,
  loadunimap, chvt, resizecons, deallocvt, getkeycodes, setkeycodes.  It
  also contains openvt, formerly called open.

  There exists a clone of the kbd package, namely console-tools, that
  contains more or less the same stuff. The latest version, console-
  tools-0.3.3 is roughly up-to-date with kbd-0.99.

  SVGATextMode-1.10 contains SVGATextMode, a program that obsoletes
  resizecons.

  util-linux-2.11 contains setterm.

  sh-utils-1.12 contains stty.

  See also dynamic-vc-1.2.tar.gz and consd-1.3.tgz for programs that
  exploit the `Keyboard Signal' key. Very primitive versions are
  spawn_login or spawn_console found in the kbd package.

  See font.tgz for a package that handles console fonts.

  Packages like recode and konwert-1.8 allow one to convert between
  different character encodings.


  The X distribution contains xmodmap, xset, kbd_mode.  (See also
  X386keybd(1) for the situation under XFree86 1.3, and Xserver(1) for
  the XKEYBOARD extension under X11R6.)  A handy interface to xmodmap is
  xkeycaps, see http://www.jwz.org/xkeycaps/.

  termcap-2.0.8.tar.gz contains termcap, an old terminal capabilities
  data base. ncurses-1.9.9e.tar.gz contains the termlib data base which
  obsoletes termcap. (However, there are still many programs using
  termcap.)

  See loadkeys(1), setleds(1) and setmetamode(1) for the codes generated
  by the various keys and the setting of leds when not under X. Under X,
  see xmodmap(1) and xset(1).

  See setfont(8) for loading console fonts. Many people will want to
  load a font like iso01.f16 because the default font is the hardware
  font of the video card, and often is a `Code Page 437' font missing
  accented characters and other Latin-1 symbols.

  See setterm(1) and kbdrate(8) for properties such as foreground and
  background colors, screen blanking and character repeat rate when not
  under X.  Under X, see xset(1), also for key click and bell volume.

  The file /etc/termcap defines the escape sequences used by many
  programs addressing the console (or any other terminal).  See
  termcap(5).  A more modern version is found in /usr/lib/terminfo.  See
  terminfo(5). Terminfo files are compiled by the terminfo compiler
  /usr/lib/terminfo/tic, see tic(1).  Their contents can be examined
  using the program infocmp, see infocmp(1).

  The Linux console sequences are documented in console_codes(4).

  The package funkey by Rick van Rein provides support for all these new
  keys modern keyboards have. See rick.vanrein.org/linux/funkey.


  2.  Keyboard generalities


  You press a key, and the keyboard controller sends scancodes to the
  kernel keyboard driver. Some keyboards can be programmed, but usually
  the scancodes corresponding to your keys are fixed.  The kernel
  keyboard driver just transmits whatever it receives to the application
  program when it is in scancode mode, like when X is running.
  Otherwise, it parses the stream of scancodes into keycodes,
  corresponding to key press or key release events.  (A single key press
  can generate up to 6 scancodes.)  These keycodes are transmitted to
  the application program when it is in keycode mode (as used, for
  example, by showkey and some X servers).  Otherwise, these keycodes
  are looked up in the keymap, and the character or string found there
  is transmitted to the application, or the action described there is
  performed.  (For example, if one presses and releases the a key, then
  the keyboard produces scancodes 0x1e and 0x9e, this is converted to
  keycodes 30 and 158, and then transmitted as 0141, the ASCII or
  latin-1 code for `a'; if one presses and releases Delete, then the
  keyboard produces scancodes 0xe0 0x53 0xe0 0xd3, these are converted
  to keycodes 111 and 239, and then transmitted as the 4-symbol sequence
  ESC [ 3 ~, all assuming a US keyboard and a default keymap. An example
  of a key combination to which an action is assigned is Ctrl-Alt-Del.)

  The translation between unusual scancodes and keycodes can be set
  using the utility setkeycodes - only few people will need it.  The
  translation between keycodes and characters or strings or actions,
  that is, the keymap, is set using the utilities loadkeys and
  setmetamode.  For details, see getkeycodes(8), setkeycodes(8),
  dumpkeys(1), loadkeys(1), setmetamode(1). The format of the files
  output by dumpkeys and read by loadkeys is described in keymaps(5).

  Where it says `transmitted to the application' in the above
  description, this really means `transmitted to the terminal driver'.
  That is, further processing is just like that of text that comes in
  over a serial line.  The details of this processing are set by the
  program stty.



  3.  Console generalities


  Conversely, when you output something to the console, it first
  undergoes the standard tty processing, and then is fed to the console
  driver.  The console driver emulates a VT100, and parses the input in
  order to recognize VT100 escape sequences (for cursor movement, clear
  screen, etc.).  The characters that are not part of an escape sequence
  are first converted into Unicode, using one of four mapping tables if
  the console was not in UTF-8 mode to start with, then looked up in the
  table describing the correspondence between Unicode values and font
  positions, and the obtained 8- or 9-bit font indices are then written
  to video memory, where they cause the display of character shapes
  found in the video card's character ROM.  One can load one's own fonts
  into character ROM using setfont.  The obsolete programs loadunimap
  and mapscrn can be used to manipulate the Unicode map belonging to the
  font, or the mapping table of the console. More details will be given
  below.

  There are many consoles (called Virtual Consoles or Virtual Terminals,
  abbreviated VCs or VTs) that share the same screen. You can use them
  as independent devices, either to run indendent login sessions, or
  just to send some output to, perhaps from top, or the tail of the
  system log or so.  See below (`Console switching') on how to set them
  up and switch between them.



  4.  Resetting your terminal


  There is garbage on the screen, or all your keystrokes are echoed as
  line drawing characters. What to do?

  Many programs will redraw the screen when Ctrl-L is typed. This might
  help when there is some modem noise or broadcast message on your
  screen.  The command clear will clear the screen.

  The command reset will reset the console driver. This helps when the
  screen is full of funny graphic characters, and also if it is reduced
  to the bottom line. If you don't have this command, or if it does
  something else, make your own by putting the following two lines in an
  executable file reset in your PATH:


               #!/bin/sh
               echo -e \\033c



  that is, you want to send the two characters ESC c to the console.

  Why is it that the display sometimes gets confused and gives you a
  24-line or 1-line screen, instead of the usual 25 lines?  Well, the
  main culprit is the use of TERM=vt100 (or some other entry with 24
  lines) instead of TERM=linux when logged in remotely.  If this happens
  on /dev/tty2 then typing


               % cat > /dev/tty2
               ^[c
               ^D



  on some other VT (where 4 symbols are typed to cat: ESC, c, ENTER,
  Ctrl-D) and refreshing the screen on /dev/tty2 (perhaps using Ctrl-L)
  will fix things. Of course the permanent fix is to use the right term­
  cap or terminfo entry.  A command that only changes the number of
  lines is


               % echo -e "\033[1;25r"



  Why is it that you sometimes get a lot of line-drawing characters,
  e.g., after catting a binary to the screen?  Well, there are various
  character set changing escape sequences, and by accident your binary
  might contain some of these.  The ESC c is a general reset, a cure for
  all, but if you know precisely what went wrong you can repair it
  without resetting other console attributes. For example, after


               % cat
               ^N
               ^D



  your shell prompt will be all line-drawing characters.  Now do (typing
  blindly)


               % cat
               ^O
               ^D



  and all is well again. (Three symbols typed to each cat: Ctrl-N (or
  Ctrl-O), ENTER, Ctrl-D.) To understand what is happening, see `The
  console character sets' below.

  If you loaded some strange font, and want to return to the default,


               % setfont



  will do (provided you stored the default font in the default place).
  If this default font does not contain an embedded Unicode map (and
  gives the wrong symbols for accented characters), then say


               % loadunimap



  For example, if I do


               % loadkeys de-latin1


  then I have a German keyboard, and the key left of the Enter key gives
  me a-umlaut. This works, because the a-umlaut occurs on the CP437 code
  page and the kernel Unicode map is initialized to CP437, and my video
  card has a CP437 font built-in.  If I now load an ISO 8859-1 font with


               % setfont iso01.f16



  then everything still works, because setfont invalidates the kernel
  Unicode map (if there is no Unicode map attached to the font), and
  without map the kernel goes directly to the font, and that is pre­
  cisely correct for an ISO 8859-1 system with iso01.f16 font.  But
  going back to the previous font with


               % setfont



  gives capital Sigma's instead of a-umlaut - all accented letters are
  mixed up because also this font has no embedded Unicode map. After


               % loadunimap



  which loads the default Unicode map (which is right for the default
  font) all works correctly again. Usually loadunimap is not invoked
  directly, but via setfont. Thus, the previous two commands may be
  replaced by


               % setfont -u def



  These days most fonts have embedded Unicode maps (often this is indi­
  cated by the extension .psfu), and none of this nonsense is needed
  anymore.

  On very old terminals output involving tabs may require a delay, and
  you have to say


               % stty tab3



  (see stty(1)).

  You can change the video mode using resizecons or SVGATextMode. Or by
  rebooting and having "vga=ask" in the LILO configuration file.

  This usually settles the output side.

  On the input side there are many things that might be wrong. If X or
  DOOM or some other program using raw mode crashed, your keyboard may
  still be in raw (or mediumraw) mode, and it is difficult to give
  commands.  (See "How to get out of raw mode" below.)  If you loaded a
  bad keymap, then


               % loadkeys -d



  loads the default map again, but it may well be difficult to type `-'!
  An alternative is


               % loadkeys defkeymap



  Sometimes even the letters are garbled. It is useful to know that
  there are four main types of keyboards: QWERTY, QWERTZ, AZERTY and
  DVORAK.  The first three are named after the first six letter keys,
  and roughly represent the English, German and French speaking coun­
  tries.  Compared to QWERTY, the QWERTZ map interchanges Y and Z.  Com­
  pared to QWERTY, the AZERTY map interchanges Q and A, W and Z, and has
  its M right of the L, at the semicolon position.  DVORAK has an
  entirely different letter ordering.  There are two types of Turkish
  keyboard. The so-called `Q'-keyboard has a QWERTY layout, while the
  `F'-keyboard has an entirely different layout, let us say fgGIod,
  where G stands for Gbreve and I for dotlessi.


  4.1.  Keyboard hardware reset


  Things may be wrong on a lower level than Linux knows about.  There
  are at least two distinct lower levels (keyboard and keyboard
  controller) where one can give the command "keyboard disable" to the
  keyboard hardware.  Keyboards can often be programmed to use one out
  of three different sets of scancodes.

  However, I do not know of cases where this turned out to be a problem.

  Some keyboards have a remapping capability built in.  Stormy Henderson
  (stormy@Ghost.Net) writes: `If it's your keyboard accidently being
  reprogrammed, you can (on a Gateway AnyKey keyboard) press control-
  alt-suspend_macro to reset the keys to normal.'


  5.  Delete and Backspace


  Getting Delete and Backspace to work just right is nontrivial,
  especially in a mixed environment, where you talk to console, to X, to
  bash, to emacs, login remotely, etc.  You may have to edit several
  configuration files to tell all of the programs involved precisely
  what you want.  On the one hand, there is the matter of which keys
  generate which codes (and how these codes are remapped by e.g. kermit
  or emacs), and on the other hand the question of what functions are
  bound to what codes.

  People often complain `my backspace key does not work', as if this key
  had a built-in function `delete previous character'.  Unfortunately,
  all this key, or any key, does is producing a code, and one only can
  hope that the kernel tty driver and all application programs can be
  configured such that the backspace key indeed does function as a
  `delete previous character' key.
  Most Unix programs get their tty input via the kernel tty driver in
  `cooked' mode, and a simple stty command determines the erase
  character. However, programs like bash and emacs and X do their own
  input handling, and have to be convinced one-by-one to do the right
  thing.


  5.1.  How to tell Unix what character you want to use to delete the
  last typed character



               % stty erase ^?



  If the character is erased, but in a funny way, then something is
  wrong with your tty settings. If echoprt is set, then erased charac­
  ters are enclosed between \ and /.  If echoe is not set, then the
  erase char is echoed (which is reasonable when it is a printing char­
  acter, like #).  Most people will want stty echoe -echoprt. Saying
  stty sane will do this and more. Saying stty -a shows your current
  settings.  How come this is not right by default? It is, if you use
  the right getty.

  Note that many programs (like bash, emacs etc.) have their own
  keybindings (defined in ~/.inputrc, ~/.emacs etc.) and are unaffected
  by the setting of the erase character.

  The standard Unix tty driver does not recognize a cursor, or keys
  (like the arrow keys) to move the current position, and hence does not
  have a command `delete current character' either. But for example you
  can get bash on the console to recognize the Delete key by putting


               set editing-mode emacs
               "\e[3~":delete-char



  into ~/.inputrc.


  5.1.1.  `Getty used to do the right thing with DEL and BS but is bro­
  ken now?'


  Earlier, the console driver would do BS Space BS (\010\040\010) when
  it got a DEL (\177).  Nowadays, DEL's are ignored (as they should be,
  since the driver emulates a vt100). Get a better getty, i.e., one that
  does not output DEL.


  5.1.2.  `Login behaves differently at the first and second login
  attempts?'


  At the first attempt, you are talking to getty. At the second attempt,
  you are talking to login, a different program.



  5.2.  How to tell Linux what code to generate when a key is pressed


  On the console, or, more precisely, when not in (MEDIUM)RAW mode, use


               % loadkeys mykeys.map



  and under X use


               % xmodmap mykeys.xmap



  Note that (since XFree86-2.1) X reads the Linux settings of the
  keymaps when initialising the X keymap. Although the two systems are
  not 100% compatible, this should mean that in many cases the use of
  xmodmap has become superfluous.

  For example, suppose that you would like the Backspace key to send a
  BackSpace (Ctrl-H, octal 010) and the grey Delete key a DEL (octal
  0177). Add the following to /etc/rc.local (or wherever you keep your
  local boot-time stuff):


               /usr/bin/loadkeys << EOF
               keycode 14 = BackSpace
               keycode 111 = Delete
               EOF



  Note that this will only change the function of these keys when no
  modifiers are used. (You need to specify a keymaps line to tell which
  keymaps should be affected if you want to change bindings on more
  keymaps.)  The Linux kernel default lets Ctrl-Backspace generate
  BackSpace - this is sometimes useful as emergency escape, when you
  find you can only generate DELs.

  The left Alt key is sometimes called the Meta key, and by default the
  combinations AltL-X are bound to the symbol MetaX.  But what character
  sequence is MetaX?  That is determined (per-tty) by the Meta flag, set
  by the command setmetamode. The two choices are: ESC X or X or-ed with
  0200.

  Many distributions have a loadkeys command somewhere in the bootup
  sequence. For example, one may have the name of the desired keymap in
  /etc/sysconfig/keyboard and the loadkeys command that loads it in
  /etc/rc.d/init.d/keytable.  Or one may have the actual default keymap
  in /etc/default.keytab and the loadkeys command that loads it in
  /etc/rc.d/boot.  Etc. Instead of adding a local modification to the
  default, one can of course change the default by editing the default
  keymap or changing the name of the keymap to be loaded at boot time.
  Note that loadkeys itself has default keymap defkeymap.map located
  somewhere under /usr/lib/kbd or /usr/share/kbd (just like all other
  keymaps) and this may not yet be available in single user boot before
  /usr has been mounted.



  5.2.1.  `How do I get a dvorak keyboard?'

  The command


               % loadkeys dvorak



  will give you a dvorak layout, probably by loading something like
  /usr/lib/kbd/keymaps/i386/dvorak/dvorak.map.gz.  Under X, put


               XkbLayout       "dvorak"



  in XF86Config.


  5.2.2.  `Why doesn't the Backspace key generate BackSpace by default?'


  (i) Because the VT100 had a Delete key above the Enter key.

  (ii) Because Linus decided so.


  5.3.  How to tell X to interchange Delete and Backspace



               % xmodmap -e "keysym BackSpace = Delete" -e "keysym Delete = BackSpace"



  Or, if you just want the Backspace key to generate a BackSpace:


               % xmodmap -e "keycode 22 = BackSpace"



  Or, if you just want the Delete key to generate a Delete:


               % xmodmap -e "keycode 107 = Delete"



  (but usually this is the default binding already).


  5.4.  How to tell emacs what to do when it receives a Delete or
  Backspace


  Put in your .emacs file lines like


          (global-set-key "\?" 'help-command)
          (global-set-key "\C-h" 'delete-backward-char)



  Of course you can bind other commands to other keys in the same way.
  Note that various major and minor modes redefine keybindings.  For
  example, in incremental search mode one finds the code


               (define-key map "\177" 'isearch-delete-char)
               (define-key map "\C-h" 'isearch-mode-help)



  This means that it may be a bad idea to use the above two global-set-
  key commands. There are too many places where there are built-in
  assumptions about Ctrl-H = help and DEL = delete.  That doesn't mean
  that you have to setup keys so that Backspace generates DEL. But if it
  doesn't then it is easiest to remap them at the lowest possible level
  in emacs.


  5.5.  How to tell emacs to interchange Delete and Backspace


  Put in your .emacs file lines


               (setq keyboard-translate-table (make-string 128 0))
               (let ((i 0))
                 (while (< i 128)
                   (aset keyboard-translate-table i i)
                   (setq i (1+ i))))
               (aset keyboard-translate-table ?\b ?\^?)
               (aset keyboard-translate-table ?\^? ?\b)



  Recent versions of emacs have a function keyboard-translate and one
  may simplify the above to


               (keyboard-translate ?\C-h ?\C-?)
               (keyboard-translate ?\C-? ?\C-h)



  Note that under X emacs can distinguish between Ctrl-h and the
  Backspace key (regardless of what codes these produce on the console),
  and by default emacs will view the Backspace key as DEL (and do dele­
  tion things, as bound to that character, rather than help things,
  bound to Ctrl-H). One can distinguish Backspace and Delete, e.g. by


               (global-unset-key [backspace] )
               (global-set-key [backspace] 'delete-backward-char)
               (global-unset-key [delete] )
               (global-set-key [delete] 'delete-char)



  5.6.  How to tell kermit to interchange Delete and Backspace


  Put in your .kermrc file the lines


               set key \127 \8
               set key \8 \127



  5.7.  How to tell xterm to interchange Delete and Backspace



       XTerm*VT100.Translations:       #override\n\
               <KeyPress> BackSpace : string(0x7f)\n\
               <KeyPress> Delete : string(0x08)\n



  5.8.  How to tell xterm about your favourite tty modes


  Normally xterm will inherit the tty modes from its invoker.  Under
  xdm, the default erase and kill characters are # and @, as in good old
  Unix Version 6.  If you don't like that, you might put something like


               XTerm*ttymodes: erase ^? kill ^U intr ^C quit ^\ eof ^D \
                               susp ^Z start ^Q stop ^S eol ^@



  in /usr/lib/X11/app-defaults/XTerm or in $HOME/.Xresources, assuming
  that you have a line


               xrdb -merge $HOME/.Xresources



  in your $HOME/.xinitrc or $HOME/.xsession.


  5.9.  How to tell non-Motif X applications that the Del key deletes
  forward

  Put


       *Text.translations:    #override \
               ~Shift ~Meta <Key>Delete: delete-next-character()



  into .Xresources to make non-Motif X applications such as xfig, xedit,
  etc., work correctly. (Daniel T. Cobra)

  5.10.  How to tell xmosaic that the Backspace key generates a DEL


  Putting


               *XmText.translations: #override\n\
                  <Key>osfDelete: delete-previous-character()
               *XmTextField.translations: #override\n\
                  <Key>osfDelete: delete-previous-character()



  in your $HOME/.Xdefaults or $HOME/.Xresources helps.  (What file? The
  file that is fed to xrdb, for example in .xinitrc.)

  The netscape FAQ, however, says:

          Why doesn't my Backspace key work in text fields?
          By default, Linux and XFree86 come with the Backspace and Delete keys
          misconfigured. All Motif programs (including, of course, Netscape
          Navigator) will malfunction in the same way.

          The Motif spec says that Backspace is supposed to delete the previous
          character and Delete is supposed to delete the following character.
          Linux and XFree86 come configured with both the Backspace and Delete
          keys generating Delete.

          You can fix this by using any one of the xmodmap, xkeycaps, or
          loadkeys programs to make the key in question generate the BackSpace
          keysym instead of Delete.

          You can also fix it by having a .motifbind file; see the man page
          for VirtualBindings(3).

          Note: Don't use the *XmText.translations or *XmTextField.translations
          resources to attempt to fix this problem. If you do, you will blow
          away Netscape Navigator's other text-field key bindings.



  5.11.  A better solution for Motif-using programs, like netscape


  Ted Kandell (ted@tcg.net) suggests the following:

  Somewhere in your .profile add the following:


       stty erase ^H



  If you are using bash, add the following lines to your .inputrc:


       "\C-?": delete-char
       "\C-h": backward-delete-char



  Add the following lines to your .xinitrc file:
       xmodmap <<-EOF
       keycode 22  =  BackSpace osfBackSpace
       keycode 107 =  Delete
       EOF

       # start your window manager here,  for example:
       #(fvwm) 2>&1 | tee /dev/tty /dev/console

       stty sane
       stty erase ^H
       loadmap <<-EOF
       keycode 14  = BackSpace
       keycode 111 = Delete
       EOF



  This will definitely work for a PC 101 or 102 key keyboard with any
  Linux/XFree86 layout.

  The important part to making Motif apps like Netscape work properly is
  adding osfBackSpace to keycode 22 in addition to BackSpace.

  Note that there must be spaces on either side of the = sign.



  5.12.  What about termcap and terminfo?


  When people have problems with backspace, they tend to look at their
  termcap (or terminfo) entry for the terminal, and indeed, there does
  exist a kb (or kbs) capability describing the code generated by the
  Backspace key.  However, not many programs use it, so unless you are
  having problems with one particular program only, probably the fault
  is elsewhere.  Of course it is a good idea anyway to correct your
  termcap (terminfo) entry.  See also below under "The TERM variable".


  5.13.  A complete solution

  There are many possibilities to get a functioning system.  Can't you
  give one complete set of settings that works?

  One way of getting a setup that works in all contexts is to have the
  Backspace key generate DEL when on the console (or xterm), and
  BackSpace when under X.  Maybe that is most convenient - there are too
  many X utilities that expect BackSpace, and emacs on the console or
  xterm expects DEL, while emacs under X can distinguish [BackSpace]
  from Ctrl-H and does the right thing.

  What is needed?  No loadkeys changes, since the Backspace key already
  generates DEL by default.  No stty settings, they are OK by default.
  No X settings, they are OK by default.  One just has to tell xterm
  that the Backspace key should generate DEL: put


       XTerm*VT100.Translations:       #override\n\
               <KeyPress> BackSpace : string(0x7f)\n\



  in .Xresources, and

  xrdb -merge .Xresources



  in .xinitrc, and you are settled.

  For a much more extensive discussion of these things, and alternative
  solutions, see Anne Baretta's page.


  6.  The console character sets


  The kernel first tries to figure out what symbol is meant by any given
  user byte, and next where this symbol is located in the current font.

  The kernel knows about 5 translations of bytes into console-screen
  symbols.  In Unicode (UTF-8) mode, the UTF-8 code is just converted
  directly into Unicode. The assumption is that almost all symbols one
  needs are present in Unicode, and for the cases where this does not
  hold the codes 0xf000-0xf1ff are reserved for direct font access.
  When not in Unicode mode, one of four translation tables is used.  The
  four tables are: a) Latin1 -> Unicode,  b) VT100 graphics -> Unicode,
  c) PC -> Unicode, d) user-defined.

  There are two character sets, called G0 and G1, and one of them is the
  current character set. (Initially G0.)  Typing Ctrl-N causes G1 to
  become current, Ctrl-O causes G0 to become current.

  These variables G0 and G1 point at a translation table, and can be
  changed by the user. Initially they point at tables a) and b),
  respectively.  The sequences ESC ( B and ESC ( 0 and ESC ( U and ESC (
  K cause G0 to point at translation table a), b), c) and d),
  respectively.  The sequences ESC ) B and ESC ) 0 and ESC ) U and ESC )
  K cause G1 to point at translation table a), b), c) and d),
  respectively.

  The sequence ESC c causes a terminal reset, which is what you want if
  the screen is all garbled. The oft-advised echo ^V^O will only make G0
  current, but there is no guarantee that G0 points at table a).  In
  some distributions there is a program reset(1) that just does echo
  ^[c.  If your termcap entry for the console is correct (and has an
  entry :rs=\Ec:), then also setterm -reset will work.

  The user-defined mapping table can be set using mapscrn(8).  The
  result of the mapping is that if a symbol c is printed, the symbol s =
  map[c] is sent to the video memory. The bitmap that corresponds to s
  is found in the character ROM, and can be changed using setfont(8).


  7.  Console switching


  By default, console switching is done using Alt-Fn or Ctrl-Alt-Fn.
  Under X (or recent versions of dosemu), only Ctrl-Alt-Fn works.  Many
  keymaps will allow cyclic walks through all allocated consoles using
  Alt-RightArrow and Alt-LeftArrow.

  XFree86 1.3 does not know that Alt is down when you switch to the X
  window. Thus, you cannot switch immediately to some other VT again but
  have to release Alt first.  In the other direction this should work:
  the kernel always keeps track of the up/down status of all keys. (As
  far as possible: on some keyboards some keys do not emit a scancode
  when pressed (e.g.: the PFn keys of a FOCUS 9000) or released (e.g.:
  the Pause key of many keyboards).)
  XFree86 1.3 saves the fonts loaded in the character ROMs when started,
  and restores it on a console switch. Thus, the result of setfont on a
  VT is wiped out when you go to X and back.  Using setfont under X will
  lead to funny results.

  One can change VT under program control using the chvt command.


  7.1.  Changing the number of Virtual Consoles


  This question still comes up from time to time, but the answer is: you
  already have enough of them.  Since kernel version 1.1.54, there are
  between 1 and 63 virtual consoles. A new one is created as soon as it
  is opened. It is removed by the utility deallocvt (but it can be
  removed only when no processes are associated to it anymore, and no
  text on it has been selected by programs like selection or gpm).

  For older kernels, change the line


               #define NR_CONSOLES     8



  in include/linux/tty.h (don't increase this number beyond 63), and
  recompile the kernel.

  If they do not exist yet, create the tty devices with MAKEDEV or mknod
  ttyN c 4 N where N denotes the tty number. For example,


               for i in 9 10 11 12; do mknod /dev/tty$i c 4 $i; done



  or, better (since it also takes care of owner and permissions),


               for i in 9 10 11 12; do /dev/MAKEDEV tty$i; done



  If you want the new VCs to run getty, add lines in /etc/inittab.  (But
  it is much better to have only two getty's running, and to create more
  consoles dynamically as the need arises.  That way you'll have more
  memory when you don't use all these consoles, and also more consoles,
  in case you really need them.  Edit /etc/inittab and comment out all
  getty's except for the first two.)

  When the consoles are allocated dynamically, it is usually easiest to
  have only one or two running getty. More are opened by open -l -s
  bash. Unused consoles (without associated processes) are deallocated
  using deallocvt (formerly disalloc).  But, you say, I am involved in
  activities when I suddenly need more consoles, and do not have a bash
  prompt available to give the open command.  Fortunately it is possible
  to create a new console upon a single keystroke, regardless of what is
  happening at the current console.

  If you have spawn_login from kbd-1.04.tar.gz and you put



          loadkeys << EOF
          alt keycode 103 = Spawn_Console
          EOF
          spawn_login &



  in /etc/rc.local, then typing Alt-UpArrow will create a fresh VC run­
  ning login (and switch to it). With spawn_console & instead of
  spawn_login & you'll have bash running there.  See also open-1.4.tgz
  and dynamic-vc-1.1.tar.gz.

  What action should be taken upon this Spawn_Console keypress can also
  be set in /etc/inittab under kbrequest, if you have a recent init. See
  inittab(5).

  (This action can be something entirely different - I just called the
  key Spawn_Console because that is what I used it for.  When used for
  other purposes it is less confusing to use its synonym KeyboardSignal.
  For example, some people like to put the lines


               kb::kbrequest:/sbin/shutdown -h now



  in /etc/inittab, and


               control alt keycode 79 = KeyboardSignal
               control alt keycode 107 = KeyboardSignal



  in their keymap. Now Ctrl-Alt-End will do a system shutdown.)

  You can only login as "root" on terminals listed in /etc/securetty.
  There exist programs that read terminal settings from files /etc/ttys
  and /etc/ttytype. If you have such files, and create additional
  consoles, then it might be a good idea to also add entries for them in
  these files.


  8.  Ctrl-Alt-Del and other special key combinations



  8.1.  Ctrl-Alt-Del (Boot)


  If you press Ctrl-Alt-Del (or whatever key was assigned the keysym
  Boot by loadkeys) then either the machine reboots immediately (without
  sync), or init is sent a SIGINT. The former behaviour is the default.
  The default can be changed by root, using the system call reboot(),
  see ctrlaltdel(8).  Some init's change the default. What happens when
  init gets SIGINT depends on the version of init used - often it will
  be determined by the pf entry in /etc/inittab (which means that you
  can run an arbitrary program in this case).  In the current kernel
  Ctrl-AltGr-Del is no longer by default assigned to Boot.



  8.2.  Other combinations



  Name            Default binding
  -------------------------------
  Show_Memory     Shift-Scrollock
  Show_Registers  AltGr-ScrollLock
  Show_State      Ctrl-ScrollLock
  Console_n       Alt-Fn and Ctrl-Alt-Fn  (1 <= n <= 12)
  Console_{n+12}  AltGr-Fn                (1 <= n <= 12)
  Incr_Console    Alt-RightArrow
  Decr_Console    Alt-LeftArrow
  Last_Console    Alt[Gr]-PrintScreen
  Scroll_Backward Shift-PageUp
  Scroll_Forward  Shift-PageDown
  Caps_On                                 (CapsLock is a toggle; this key sets)
  Compose         Ctrl-.



  8.3.  X Combinations



  Ctrl-Alt-Fn     Switch to VT n
  Ctrl-Alt-KP+    Next mode
  Ctrl-Alt-KP-    Previous mode
  Ctrl-Alt-Backspace      Kill X


  On some motherboards, Ctrl-Alt-KP- and Ctrl-Alt-KP+ will be equivalent
  to pressing the Turbo button. That is, both will produce the scancodes
  1d 38 4a ca b8 9d and 1d 38 4e ce b8 9d, and both will switch between
  Turbo (>= 25MHz) and non-Turbo (8 or 12 MHz).  (Often these key combi­
  nations only function this way when enabled by jumpers on the mother­
  board.)

  Perry F Nguyen (pfnguyen@netcom22.netcom.com) writes: AMI BIOS has a
  feature that locks up the keyboard and flashes the LED's if the Ctrl-
  Alt-Backspace combination is pressed while a BIOS password is enabled,
  until the CMOS/BIOS password is typed in.

  On some SiS based motherboards the combination Ctrl-Alt-Backspace will
  cause a power off, or puts the machine in power save mode.  (Reported
  for SiS 630 and for SiS645DX.)


  8.4.  Dosemu Combinations



  Ctrl-Alt-Fn     Switch to VT n (from version 0.50; earlier Alt-Fn)
  Ctrl-Alt-PgDn   Kill dosemu (when in RAW keyboard mode)
  (and many other combinations - see the dosemu documentation)



  8.5.  Composing symbols


  One symbol may be constructed using several keystrokes.


  ·  LeftAlt-press, followed by a decimal number typed on the keypad,
     followed by LeftAlt-release, yields the symbol with code given by
     this number.  (In Unicode mode this same mechanism, but then with 4
     hexadecimal digits, may be used to define a Unicode symbol.)

  ·  A dead diacritic followed by a symbol, yields that symbol adorned
     with that diacritic. If the combination is undefined, both keys are
     taken separately.  Which keys are dead diacritics is user-settable;
     none is by default.  Five (since 2.0.25 six) dead diacritics can be
     defined (using loadkeys(1)): dead_grave, dead_acute,
     dead_circumflex, dead_tilde, dead_diaeresis (and dead_cedilla).
     Precisely what this adorning means is also user-settable: dead-
     diacritic, symbol is equivalent to Compose + diacritic + symbol.

  ·  Compose followed by two symbols yields a combination symbol. These
     combinations are user-settable. Today there are 68 combinations
     defined by default; you can see them by saying "dumpkeys | grep
     compose".

  ·  Then there are `Sticky' modifier keys (since 1.3.33). For example,
     one can type Ctrl-C as SControl, C and Ctrl-Alt-BackSpace as
     SControl, SAlt, BackSpace.

  Note that there are at least four such composition mechanisms:

  1. The Linux keyboard driver mechanism, used in conjunction with
     loadkeys.

  2. The X mechanism - see X386keybd(1), later XFree86kbd(1).  Under
     X11R6: edit /usr/X11R6/lib/X11/locale/iso8859-1/Compose.

     See also Andrew D. Balsa's comments at
     http://wauug.erols.com/~balsa/linux/deadkeys/index.html.

  3. The emacs mechanism obtained by loading "iso-insert.el" or calling
     `iso-accents-mode'.

  4. The vim mechanism: insert a composed symbol by pressing Ctrl-K
     followed by two symbols. A list of the possible combinations is
     obtained by the command :digraphs.

     For X the order of the two symbols is arbitrary: both Compose-,-c
     and Compose-c-, yield a c-cedilla; for Linux and emacs only the
     former sequence works by default. For X and vim the list of compose
     combinations is fixed.  Linux and emacs are flexible.  The default
     lists are somewhat similar, but the details are different.


  8.6.  The SysRq key

  In case your kernel was compiled with CONFIG_MAGIC_SYSRQ enabled (a
  feature that is present since Linux 2.1.43) there is a single key
  (defined in <linux/keyboard.h>) to which special system functions are
  attached, regardless of the current keyboard mode. For the PC
  architecture this special key is, naturally, the Alt+SysRq key, and
  any of the two Alt keys will work.  (Note that if CONFIG_MAGIC_SYSRQ
  was not enabled, the default action of this key is to return to the
  previous console.)

  If you press this key, do not release it, and hit another key, a
  corresponding action is performed. The action is performed whether
  anybody is logged in or not, is root or not. For the details, see
  drivers/char/sysrq.c. Since this feature is meant only for kernel
  hackers, that should suffice. Still, let me add a few remarks.


  For the key r the keyboard mode is reset to K_XLATE.  For the key k a
  SAK and console reset is done.  For the key b the machine is rebooted
  immediately.  (See, not something you want to have enabled on a
  production machine.)  For the key o the power is turned off (when the
  machine is capable of that).  For the key s an emergency sync is
  scheduled.  For the key u an emergency read-only remount is scheduled.
  For the keys p,t,m various information is shown (namely the same
  information also shown for RAlt,RCtrl,RShift+ScrollLock).  For the
  keys e,i,l all processes get a SIG_TERM or SIG_KILL, respectively; for
  l even the init process is killed.  Digits set the log level. Anything
  else prints a short summary: SysRq: unRaw saK Boot Off Sync Unmount
  showPc showTasks showMem loglevel0-8 tErm kIll killalL.

  Note: These are very dangerous actions! And they do not use your
  keymap - indeed, are meant for emergency cases where the state of your
  keymap, or even of the entire kernel, is uncertain.  If you use a
  dvorak keyboard - bad luck! Most other people will be able to survive:
  the dangerous letters A,M,Q,W,Y,Z that are differently placed on
  English, French and German keyboards, are not used for actions. (But
  if your finger slips and you hit L instead of K - bye bye to your
  system.)

  In Linux 2.3.13 the possibility to enable/disable SysRq was added.


               echo 0 > /proc/sys/kernel/sysrq



  will disable it (if the kernel was compiled with CONFIG_MAGIC_SYSRQ).


  8.7.  Problems

  A good keyboard accurately reports multiple key presses.  Especially
  for people using a keyboard as Braille input device, where they have
  to be able to press up to six keys simultaneously, this is important.
  Many modern keyboards fail here due to sloppy design and testing -
  they misreport or fail in other ways when four or more keys are
  pressed simultaneously, sometimes already when two non-modifier keys
  are pressed simultaneously.  This affects Linux users a bit: the SysRq
  key is not a modifier key, and people report problems using Alt-SysRq-
  X for various letters or digits X.

  Long ago a similar problem (`ghosting') was caused by the design of
  the scan matrix: when three keys were pressed a fourth was also seen.
  That problem was solved by the use of diodes.  Today it is the
  interface logic that is deficient.


  9.  How to get out of raw mode


  If some program using K_RAW keyboard mode exits without restoring the
  keyboard mode to K_XLATE, then it is difficult to do anything - not
  even Ctrl-Alt-Del works. However, it is sometimes possible to avoid
  hitting the reset button.  (And desirable as well: your users may get
  angry if you kill their Hack game by rebooting; you might also damage
  your file system.)  Easy solutions involve logging in from another
  terminal or another machine and doing kbd_mode -a.  The procedure
  below assumes that no X is running, that the display is in text mode,
  and that you are at your bash prompt, that you are using a US keyboard
  layout, and that your interrupt character is Ctrl-C.


  Step 1. Start X.  As follows: press 2 (and don't release), press F12
  (and don't release) and immediately afterwards press = . This starts
  X.  (Explanation: if a key press produces keycode K, then the key
  release produces keycode K+128. Probably your shell does not like
  these high characters, so we avoid generating them by not releasing
  any key.  However, we have to be quick, otherwise key repeat starts.
  The digit 2 produces a Ctrl-C that discards previous junk, the F12
  produces an X and the = a Return.)  Probably your screen will be grey
  now, since no .xinitrc was specified.  However, Ctrl-Alt-Fn will work
  and you can go to another VT.  (Ctrl-Alt-Backspace also works, but
  that exits X, and gets you back into the previous state, which is not
  what you want.)

  Step 2. Setup to change the keyboard mode.  (For example, by sleep 5;
  kbd_mode -a.)

  Step 3. Leave X again.  Alt-Fx (often Alt-F7) brings you back to X,
  and then Ctrl-Alt-Backspace exits X. Within 5 seconds your keyboard
  will be usable again.

  If you want to prepare for the occasion, then make \215A\301 (3
  symbols) an alias for kbd_mode -a.  Now just hitting = F7 = (3
  symbols) will return you to sanity.


  10.  The keyboard LEDs


  1. There are per-tty keyboard flags: each VC has its own NumLock,
  CapsLock, ScrollLock.  By default these keyboard flags are shown in
  the LEDs.  The usual way to change them is by pressing the
  corresponding key.  (Side remark: pressing the NumLock key when in
  application key mode will not change the NumLock status, but produce
  an escape sequence.  If you want the NumLock key to always change the
  Numlock status, bind it to Bare_Num_Lock.)

  2. Next, there are per-tty default keyboard flags, to initialize the
  keyboard flags when a reset occurs.  Thus if you want NumLock on all
  the time, that is possible.  The usual way to change them is by
  `setleds -D ...'.

  3. There is the possibility that the leds do not reflect the keyboard
  flags, but something else.

  3A. This something else can be three bits somewhere in the kernel -
  which can be used if you want to monitor some hardware or software
  status bit(s). If you want this, edit the kernel source to call
  register_leds() somewhere.

  3B. This something else can also be whatever some user program wants
  to show in the LEDs. Thus, people who like such things can make nice
  patterns of lights. If you want this, use the KDSETLED ioctl.

  This latter use is not per-tty, but the choice between former and
  latter use is per-tty.

  Summarizing: Each tty has a flag kbd->ledmode.  If this has the value
  LED_SHOW_FLAGS then the keyboard flags (NumLock etc.) of that tty are
  shown.  If this has the value LED_SHOW_MEM then three selected memory
  addresses are shown.  If this has the value LED_SHOW_IOCTL then the
  leds show whatever value was last assigned to them using the KDSETLED
  ioctl.

  One may add that X uses ioctl's to set the LEDs, but fails to reset
  its VT when it exits, so after using X there may be one VT that is not
  in the default LED_SHOW_FLAGS state.  This can be fixed by doing
  `setleds -L' on that VT.  See setleds(1).


  11.  The TERM variable


  Many programs use the TERM variable and the database /etc/termcap or
  /usr/lib/terminfo/* to decide which strings to send for clear screen,
  move cursor, etc., and sometimes also to decide which string is sent
  by the users backspace key, function keys etc.  This value is first
  set by the kernel (for the console).  Usually, this variable is re-set
  by getty, using /etc/ttytype or the argument specified in
  /etc/inittab.  Sometimes, it is also set in /etc/profile.

  Older systems use TERM=console or TERM=con80x25. Newer systems (with
  ncurses 1.8.6) use the more specific TERM=linux or TERM=linux-80x25.
  However, old versions of setterm test for TERM=con* and hence fail to
  work with TERM=linux.

  Since kernel version 1.3.2, the kernel default for the console is
  TERM=linux.

  If you have a termcap without entry for linux, add the word linux to
  the entry for the console:


               console|con80x25|linux:\



  and make /usr/lib/terminfo/l/linux a copy of or symbolic link to
  /usr/lib/terminfo/c/console.


  11.1.  Terminfo


  The terminfo entry for the linux console from ncurses 1.8.6 misses the
  entry kich1=\E[2~, needed by some programs.  Edit the file and tic it.


  12.  How to make other programs work with non-ASCII chars


  In the bad old days this used to be quite a hassle. Every separate
  program had to be convinced individually to leave your bits alone.
  Not that all is easy now, but recently a lot of gnu utilities have
  learned to react to LC_CTYPE=iso_8859_1 or LC_CTYPE=iso-8859-1.  Try
  this first, and if it doesn't help look at the hints below.  Note that
  in recent versions of libc the routine setlocale() only works if you
  have installed the locale files (e.g. in /usr/lib/locale).

  First of all, the 8-th bit should survive the kernel input processing,
  so make sure to have stty cs8 -istrip -parenb set.

  A. For emacs the details strongly depend on the version.  The
  information below is for version 19.34. Put lines


               (set-input-mode nil nil 1)
               (standard-display-european t)
               (require 'iso-syntax)



  into your $HOME/.emacs.  The first line (to be precise: the final 1)
  tells emacs not to discard the 8-th bit from input characters.  The
  second line tells emacs not to display non-ASCII characters as octal
  escapes.  The third line specifies the syntactic properties and case
  conversion table for the Latin-1 character set These last two lines
  are superfluous if you have something like LC_CTYPE=ISO-8859-1 in your
  environment.  (The variable may also be LC_ALL or even LANG.  The
  value may be anything with a substring `88591' or `8859-1' or
  `8859_1'.)

  This is a good start.  On a terminal that cannot display non-ASCII ISO
  8859-1 symbols, the command


               (load-library "iso-ascii")



  will cause accented characters to be displayed comme {,c}a.  If your
  keymap does not make it easy to produce non-ASCII characters, then


               (load-library "iso-transl")



  will make the 2-character sequence Ctrl-X 8 a compose character, so
  that the 4-character sequence Ctrl-X 8 , c produces c-cedilla.  Very
  inconvenient.

  The command


               (iso-accents-mode)



  will toggle ISO-8859-1 accent mode, in which the six characters ', `,
  ", ^, ~, / are dead keys modifying the following symbol.  Special com­
  binations: ~c gives a c with cedilla, ~d gives an Icelandic eth, ~t
  gives an Icelandic thorn, "s gives German sharp s, /a gives a with
  ring, /e gives an a-e ligature, ~< and ~> give guillemots, ~! gives an
  inverted exclamation mark, ~? gives an inverted question mark, and ''
  gives an acute accent.  This is the default mapping of accents.  The
  variable iso-languages is a list of pairs (language name, accent map­
  ping), and a non-default mapping can be selected using


               (iso-accents-customize LANGUAGE)



  Here LANGUAGE can be one of "portuguese", "irish", "french",
  "latin-2", "latin-1".

  Since the Linux default compose character is Ctrl-.  it might be
  convenient to use that everywhere. Try


               (load-library "iso-insert.el")
               (define-key global-map [?\C-.] 8859-1-map)

  The latter line will not work under xterm, if you use emacs -nw, but
  in that case you can put


               XTerm*VT100.Translations:       #override\n\
                     Ctrl <KeyPress> . : string("\0308")



  in your .Xresources.)

  B. For less, put LESSCHARSET=latin1 in the environment.  This is also
  what you need if you see \255 or <AD> in man output: some versions of
  less will render the soft hyphen (octal 0255, hex 0xAD) this way when
  not given permission to output Latin-1.

  C. For ls, give the option -N. (Probably you want to make an alias.)

  D. For bash (version 1.13.*), put


               set meta-flag on
               set convert-meta off
               set output-meta on



  into your $HOME/.inputrc.

  E. For tcsh, use


               setenv LANG     US_en
               setenv LC_CTYPE iso_8859_1



  If you have nls on your system, then the corresponding routines are
  used.  Otherwise tcsh will assume iso_8859_1, regardless of the values
  given to LANG and LC_CTYPE. See the section NATIVE LANGUAGE SYSTEM in
  tcsh(1).  (The Danish HOWTO says: setenv LC_CTYPE ISO-8859-1; stty
  pass8)

  F. For flex, give the option -8 if the parser it generates must be
  able to handle 8-bit input. (Of course it must.)

  G. For elm, set displaycharset to ISO-8859-1.  (Danish HOWTO: LANG=C
  and LC_CTYPE=ISO-8859-1)

  H. For programs using curses (such as lynx) David Sibley reports: The
  regular curses package uses the high-order bit for reverse video mode
  (see flag _STANDOUT defined in /usr/include/curses.h).  However,
  ncurses seems to be 8-bit clean and does display iso-latin-8859-1
  correctly.

  I. For programs using groff (such as man), make sure to use -Tlatin1
  instead of -Tascii. Old versions of the program man also use col, and
  the next point also applies.

  J. For col, make sure 1) that it is fixed so as to do
  setlocale(LC_CTYPE,""); and 2) put LC_CTYPE=ISO-8859-1 in the
  environment.

  K. For rlogin, use option -8.

  L. For joe,
  metalab.unc.edu:/pub/Linux/apps/editors/joe-1.0.8-linux.tar.gz is said
  to work after editing the configuration file. Someone else said: joe:
  Put the -asis option in /isr/lib/joerc in the first column.

  M. For LaTeX: \documentstyle[isolatin]{article}.  For LaTeX2e:
  \documentclass{article}\usepackage{isolatin} where isolatin.sty is
  available from ftp.vlsivie.tuwien.ac.at/pub/8bit.

  A nice discussion on the topic of ISO-8859-1 and how to manage 8-bit
  characters is contained in the file grasp.insa-
  lyon.fr:/pub/faq/fr/accents (in French). Another fine discussion (in
  English) can be found in rtfm.mit.edu:pub/usenet-by-
  group/comp.answers/internationalization/iso-8859-1-charset.

  If you need to fix a program that behaves badly with 8-bit characters,
  one thing to keep in mind is that if you have a signed char type then
  characters may be negative, and using them as an array index will
  fail.  Several programs can be fixed by judiciously adding (unsigned
  char) casts.


  13.  X


  This FAQ/HOWTO is about the Linux keyboard and console, not about X,
  which substitutes its own handling. However, it seems useful to
  document some of the Linux keyboard and console related properties of
  X.

  First of all, when X is started (say using startx or xinit) it opens
  the first unused console, unless the desired console has been
  indicated explicitly, as in xinit -- vt12.  Note that this will fail
  when there is no device file /dev/tty12, but that it will not fail
  when the indicated console was in use already.  When X finishes, it
  will return to the original console.  While it is running one can use
  Ctrl-Alt-Fn to switch to VTn.

  The XFree86 keymap mechanism is much poorer than the Linux mechanism.
  For each keycode there are at most 4 symbols defined, namely for the 4
  keymaps plain, shift, mod, mod+shift. What is the modifier mod?  It is
  the one designated by the symbol Mode_switch.  For example, the
  command xmodmap keys.dk, where the file keys.dk contains


       keycode 64 = Mode_switch
       keycode 113 = Mode_switch
       keycode 38 = a A aring Aring
       keycode 26 = e E ae AE
       keycode 32 = o O oslash Ooblique



  will make both Alt keys into mod keys, so that Alt+a gives ĺ (a-ring),
  etc.  (Note the illogical naming of oslash and Ooblique.)  Such an
  xmodmap command can be placed in the .xinitrc shell script that is
  executed by default when X is started.


  13.1.  What precisely does XFree86-2.1 do when it initializes its
  keymap?


  Since version 2.1, XFree86 will initialize its keymap from the Linux
  keymap, as far as possible. However, Linux had 16 entries per key (one
  for each combination of the Shift, AltGr, Ctrl, Alt modifiers) and
  presently has 256 entries per key, while X has 4 entries per key (one
  for each combination of Shift, Mod), so some information is
  necessarily lost.

  First X reads the Xconfig file, where definitions of the LeftAlt,
  RightAlt, RightCtl, ScrollLock keys as Meta, ModeShift, Compose,
  ModeLock or ScrollLock might be found - see X386keybd(1), later
  XFree86kbd(1).

  For Mod the LeftAlt key is taken, unless RightCtl was defined as
  ModeShift or ModeLock, in which case RightCtl is taken, or RightAlt
  was so defined, in which case RightAlt is taken.  This determines how
  the 4 XFree86 meanings of a key are selected from the 16 Linux
  meanings.  Note that Linux today does not distinguish by default
  between the two Ctrl keys or between the two Shift keys. X does
  distinguish.

  Now the kernel keymap is read and the usually obvious corresponding X
  bindings are made. The bindings for the "action keys" Show_Memory,
  Show_State, Show_Registers, Last_Console, Console_n, Scroll_Backward,
  Scroll_Forward, Caps_On and Boot are ignored, as are the dead
  diacriticals, and the locks (except for ShiftLock), and the "ASCII-x"
  keys.

  Next, the definitions in the Xconfig file are used. (Thus, a
  definition of Compose in Xconfig will override its value as found in
  the Linux keymap.)

  What happens to the strings associated with the function keys?
  Nothing, X does not have such a concept. (But it is possible to define
  strings for function keys in xterm - note however that the window
  manager gets the keys first.)

  I don't know how to convince xterm that it should use the X keymap
  when Alt is pressed; it seems just to look at its resource
  eightBitInput, and depending on whether that is true or false either
  set the high order bit of the character, or generate an additional
  Escape character (just like setmetamode(1) does for the console).


  14.  Unusual keys and keyboards


  The two keys PrintScrn/SysRq and Pause/Break are special in that they
  have two keycodes: the former has keycode 84 when Alt is pressed
  simultaneously, and keycode 99 otherwise; the latter has keycode 101
  when Ctrl is pressed simultaneously, and keycode 119 otherwise.
  (Thus, it makes no sense to bind functions to Alt keycode 99 or Ctrl
  keycode 119.) The Pause/Break key is also special in another way: it
  does not generate key-up scancodes, but generates the entire
  6-scancode sequence on key-down.

  If you have strange keys, that do not generate any code under Linux
  (or generate messages like "unrecognized scancode"), and your kernel
  is 1.1.63 or later, then you can use setkeycodes(1) to tell the kernel
  about them. Once they have gotten a keycode from setkeycodes, they can
  be assigned a function by loadkeys.

  For example, using showkey -s one sees that Microsoft keyboards use
  the scancode sequences (in hexadecimal) e0 5b (left Windows key), e0
  5c (right Windows key), e0 5d (Menu key).  Microsoft Internet keyboard
  also uses e0 6a (Back), e0 69 (Forward), e0 68 (Stop), e0 6c (Mail),
  e0 65 (Search), e0 66 (Favorites), e0 32 (Web/Home), e0 6b (My
  Computer), e0 21 (Calculator), e0 5f (Sleep).  Use dumpkeys to see
  what keycodes are still unused.  Typically values like 89-95 and
  112-118 and 120-127 are free.  Now


               % setkeycodes e05b 125
               % setkeycodes e05c 126
               % setkeycodes e05d 127



  assigns keycodes to these scancode sequences, and


               % loadkeys
               keycode 125 = Decr_Console
               keycode 126 = Incr_Console
               keycode 127 = KeyboardSignal
               %



  would make these Windows keys go to the previous or next virtual con­
  sole, and let the Menu key create a fresh virtual console (in case you
  have something like spawn_console running).


  14.1.  Funkeys

  Many modern keyboards have buttons or keys with labels like "Vol Up",
  "Eject" etc. that suggest actions rather than strings.  Of course one
  can bind shell commands to them, but then they'll work only when you
  are at a shell prompt.  Rick van Rein wrote a package funkey
  consisting of a kernel patch and a daemon. The kernel patch creates a
  new character device, and adds a new key type to indicate which
  keystrokes should be sent to this new character device. A daemon can
  now listen to the character device, somewhat like gpm listens to the
  mouse device, and perform the actions indicated in its config file.
  See rick.vanrein.org/linux/funkey.


  15.  Examples of use of loadkeys and xmodmap


  Switching Caps Lock and Control on the keyboard (assuming you use
  keymaps 0-15; check with dumpkeys | head -1)


               % loadkeys
               keymaps 0-15
               keycode 58 = Control
               keycode 29 = Caps_Lock
               %



  Switching them under X only:


               % xmodmap .xmodmaprc



  where .xmodmaprc contains lines


               remove Lock = Caps_Lock
               remove Control = Control_L
               keysym Control_L = Caps_Lock
               keysym Caps_Lock = Control_L
               add Lock = Caps_Lock
               add Control = Control_L



  What is this about the key numbering? Backspace is 14 under Linux, 22
  under X?  Well, the numbering can best be regarded as arbitrary; the
  Linux number of a key can be found using showkey(1), and the X number
  using xev(1). Often the X number will be 8 more than the Linux number.

  Something else people like to change are the bindings of the function
  keys.  Suppose that you want to make F12 produce the string "emacs ".
  Then


               % loadkeys
               keycode 88 = F12
               string F12 = "emacs "
               %



  will do this. More explicitly, the procedure is like this: (i) find
  the keycodes of the keys to be remapped, using showkey(1).  (ii) save
  the current keymap, make a copy and edit that:


               % dumpkeys > my_keymap
               % cp my_keymap trial_keymap
               % emacs trial_keymap
               % loadkeys trial_keymap
               %



  The format of the table can be guessed by looking at the output of
  dumpkeys, and is documented in keymaps(5).  When the new keymap func­
  tions as desired, you can put an invocation


               loadkeys my_new_keymap



  in /etc/rc.local or so, to execute it automatically at boot-up.  Note
  that changing modifier keys is tricky, and a newbie can easily get
  into a situation only an expert can get out of.

  The default directory for keymaps is /usr/lib/kbd/keymaps.  The
  default extension for keymaps is .map.  For example, loadkeys uk would
  probably load /usr/lib/kbd/keymaps/i386/qwerty/uk.map.  (With kbd-0.95
  and older this would be /usr/lib/kbd/keytables and
  /usr/lib/kbd/keytables/uk.map.)


  (On my machine) /dev/console is a symbolic link to /dev/tty0, and the
  kernel regards /dev/tty0 as a synonym for the current VT.  XFree86 1.3
  changes the owner of /dev/tty0, but does not reset this after
  finishing. Thus, loadkeys or dumpkeys might fail because someone else
  owns /dev/tty0; in such a case you might run X first.  Note that you
  cannot change keyboard mappings when not at the console (and not
  superuser).


  15.1.  `I can use only one finger to type with'


  "Can the Shift, Ctrl and Alt keys be made to behave as toggles?"

  Yes, after saying


               % loadkeys
               keymaps 0-15
               keycode 29 = Control_Lock
               keycode 42 = Shift_Lock
               keycode 56 = Alt_Lock
               %



  the left Control, Shift and Alt keys will act as toggles.  The numbers
  involved are revealed by showkey (and usually are 29, 97, 42, 54, 56,
  100 for left and right control, shift and alt, respectively), and the
  functions are Control_Lock, Shift_Lock, Alt_Lock, ALtGr_Lock.

  "What about `sticky' modifier keys?"

  Since version 1.3.33, the kernel knows about `sticky' modifier keys.
  These act on the next key pressed. So, where one earlier needed the
  3-symbol sequence Shift_Lock a Shift_Lock to type `A', one can now use
  the 2-symbol sequence SShift_Lock a.  You can say


               % loadkeys
               keymaps 0-15
               keycode 54 = SShift
               keycode 97 = SCtrl
               keycode 100 = SAlt
               %



  to make the right Shift, Ctrl, Alt sticky versions of the left ones.
  This will allow you to type Ctrl-Alt-Del in three keystrokes with one
  hand.

  The keymaps line in these examples should cover all keymaps you have
  in use.  You find what keymaps you have in use by


               % dumpkeys | head -1



  15.2.  Sticky keys under X

  The following text was contributed by Piotr Mitros.

  XFree86 supports an accessibility option which allows disabled users
  to type single-handed. With sticky keys enabled, the user can hit a
  modifier key (ctrl, alt, shift) followed by another key, rather than
  having to hold the modifier key while hitting the letter.

  To enable sticky keys, first make sure the xkb extension is enabled
  (this is done during initial X server configuration and is usually
  enabled by default). Next, run the X server with the +accessx option.
  If you use startx, either run startx -- +accessx or add +accessx to
  the serverargs line in the startx script.  If you use xdm, add
  +accessx to the appropriate server line in /etc/X11/xdm/Xservers.

  It is also possible to enable X accessibility with some end-user
  utilities with a running X server.

  Once X accessibility is enabled, press the shift key five times in a
  row to enable sticky keys. To disable sticky keys, either press the
  shift key five times again, or press a key while holding a modifier
  key.

  XFree86 also supports Slow Keys, Repeat Keys, Bounce Keys and an
  audible bell. xkbcomp can be used to generate a .xkm file to enable
  these. The appropriate xkbcomp commands are listed in
  /usr/X11R6/lib/X11/xkb/compat/accessx.  Unfortunately, the exact
  process is still undocumented.


  16.  Changing the video mode


  As far as I know there are 6 ways to change resolution:

  1. At compile time: change the line


               SVGA_MODE=      -DSVGA_MODE=NORMAL_VGA



  in /usr/src/linux/Makefile.

  1A. After compilation: use rdev -v - a terrible hack, but it exists.

  2. At boot time: put vga=ask in the lilo config file, and lilo will
  ask you what video mode you want. Once you know, put vga=mypreference.

  3. At run time: A. Use the resizecons command. (This is a very
  primitive wrapper around the VT_RESIZE ioctl.)  B. Use the
  SVGATextMode command. (This is a less primitive wrapper around the
  VT_RESIZE ioctl.)

  4. Not "on the console": Under dosemu, or with svgalib etc. you can
  change the hardware video mode without the console driver being aware
  of it. Sometimes this is useful in getting resizecons or SVGATextMode
  set up: use dosemu and some DOS program to get into the desired
  videomode, dump (say from another VT) the contents of all video
  hardware registers, and use that in the initialization that resizecons
  and SVGATextMode require.  In some cases where the video mode has
  gotten into some unusable state, starting dosemu, relying on the BIOS
  to set up the video mode, and then killing dosemu (with kill -9), is
  the easiest way to get into shape again.
  16.1.  Instructions for the use of resizecons


  Get svgalib and compile the program restoretextmode.  Boot up your
  machine in all possible video modes (using vga=ask in the lilo config
  file), and write the video hardware register contents to files CxR
  (C=cols, R=rows), e.g., 80x25, 132x44, etc.  Put these files in
  /usr/lib/kbd/videomodes.  Now resizecons 132x44 will change videomode
  for you (and send SIGWINCH to all processes that need to know about
  this, and load another font if necessary).

  At present, resizecons only succeeds when there is memory enough for
  both the old and the new consoles at the same time.


  17.  Changing the keyboard repeat rate


  At startup, the Linux kernel sets the repeat rate to its maximal
  value.  For most keyboards this is reasonable, but for some it means
  that you can hardly touch a key without getting three copies of the
  corresponding symbol. Use the program kbdrate(8) to change the repeat
  rate, or, if that doesn't help, edit or remove the section

  ______________________________________________________________________
       ! set the keyboard repeat rate to the max

           mov     ax,#0x0305
           xor     bx,bx           ! clear bx
           int     0x16
  ______________________________________________________________________


  of /usr/src/linux/[arch/i386/]boot/setup.S.

  Scott Johnston (sj@zule.com) reports: `To program the repeat rate of a
  Gateway AnyKey keyboard all one has to do is press the "Repeat Rate"
  key, then a function key F1-F8, then "Repeat Rate" again.  F1 is the
  slowest possible repeat rate, and F8 is really fast.  If you somehow
  manage to mess up your AnyKey keyboard doing this, simply press Ctrl-
  Alt-SuspndMacro to reset your keyboard to factory default settings.'


  18.  Scrolling


  There are two ways to get a screen to scroll.  The first, called `hard
  scrolling', is to leave the text in video memory as it is, but change
  the viewing origin. This is very fast.  The second, called `soft
  scrolling', involves moving all screen text up or down. This is much
  slower.  The kernel console driver will write text starting at the top
  of the video memory, continuing to the bottom, then copy the bottom
  part to the top again, and continue, all the time using hard scrolling
  to show the right part on the screen.  You can scroll back until the
  top op the video memory by using Shift-PageUp (the grey PageUp) and
  scroll down again using Shift-PageDown (the grey PageDown), assuming a
  default keymap.  The amount of scrollback is thus limited to the
  amount of video memory you happen to have and you cannot increase this
  amount.  If you need more scrollback, use some program that buffers
  the text, like less or screen - by using a buffer on disk you can go
  back to what you did last week.  (One can set the amount of scrollback
  for xterm by adding a line like XTerm*saveLines: 2500 in .Xresources.)

  Upon changing virtual consoles, the screen content of the old VT is
  copied to kernel memory, and the screen content of the new VT is
  copied from kernel memory to video memory. Only the visible screen is
  copied, not all of video memory, so switching consoles means losing
  the scrollback information.

  Sometimes, hard scrolling is undesirable, for example when the
  hardware does not have the possibility to change viewing origin. The
  first example was a Braille machine that would render the top of video
  memory in Braille. There is a kernel boot-time option no-scroll to
  tell the console driver not to use hard scrolling.  See bootparam(7).


  19.  Screensaving


  setterm -blank nn will tell the console driver to blank the screen
  after nn minutes of inactivity. (With nn = 0, screensaving is turned
  off. In some old kernels this first took effect after the next
  keyboard interrupt.)

  The s option of xset(1) will set the X screensaving parameters: xset s
  off turns off the screensaver, xset s 10 blanks the screen after 10
  minutes.

  The video hardware powersaving modes can be enabled/disabled using the
  setvesablank program given in the starting comment of
  /usr/src/linux/drivers/char/vesa_blank.c.


  20.  Screen dumps


  setterm -dump N will dump the contents of the screen of /dev/ttyN to a
  file screen.dump in the current directory. See setterm(1).

  The current contents of the screen of /dev/ttyN can be accessed using
  the device /dev/vcsN (where `vcs' stands for `virtual console
  screen').  For example, you could have a clock program that displays
  the current time in the upper right hand corner of the console screen
  (see the program vcstime in kbd-1.04.tar.gz).  Just dumping the
  contents goes with cat /dev/vcsN.  These device files /dev/vcsN do not
  contain newlines, and do not contain attributes, like colors. From a
  program it is usually better to use /dev/vcsaN (`virtual console
  screen with attributes') instead - it starts with a header giving the
  number of rows and columns and the location of the cursor.  See
  vcs(4).


  21.  Some properties of the VT100 - application key mode


  : Sometimes my cursor keys or keypad keys produce strange codes?

  When the terminal is in application cursor key mode the cursor keys
  produce  Esc O x  and otherwise  Esc [ x  where x is one of A,B,C,D.
  Certain programs put the terminal in application cursor key mode; if
  you kill them with kill -9, or if they crash, then the mode will not
  be reset.

          % echo -e '\033c'


  resets all properties of the current VC. Just changing the cursor
  application key mode is done by

          % echo -e '\033[?1h'


  (set) and

          % echo -e '\033[?1l'


  (clear).

  When the terminal is in application keypad key mode the keypad keys
  produce  Esc O y  and otherwise  Esc [ z ~  for certain y and z.
  Setting application keypad key mode is done by

          % echo -e '\033='


  and

          % echo -e '\033>'


  clears it again.


  22.  Hardware incompatibility


  Several people have noticed that they lose typed characters when a
  floppy disk is active. It seems that this might be a problem with
  Uni-486WB motherboards.

  Tjalling Tjalkens (tjalling@ei.ele.tue.nl) reports very similar
  problems with "a no-brand GMB-486 UNP Vesa motherboard with AMD
  486DX2-66 CPU" - during floppy activity some keystrokes are lost,
  during floppy tape streamer (Conner C 250 MQ) activity many keystrokes
  are lost.

  Some people experience sporadic lockups - sometimes associated to hard
  disk activity or other I/O.

  Ulf Tietz (ulf@rio70.bln.sni.de) wrote: `I have had the same problems,
  when I had my motherboard tuned too fast.  So I reset all the timings
  ( CLK, wait statements etc ) to more conventional values, and the
  problems are gone.'

  Bill Hogan (bhogan@crl.com) wrote: `If you have an AMI BIOS, you might
  try setting the Gate A20 emulation parameter to "chipset" (if you have
  that option). Whenever I have had that parameter set to any of the
  other options on my machine ("fast", "both", "disabled") I have had
  frequent keyboard lockups.'

  There may be a relation between keyboard problems and the video card
  in use.

  Shawn K. Quinn (skquinn@wt.net) wrote: `I have a Zeos Pantera
  Pentium-90 that originally came with a Diamond Stealth 64 S3-based
  video card. Under X I frequently got q's inserted into my text (how
  annoying) especially if I typed very fast (during Netrek for instance,
  even more annoying because guess what that does :-( ).  Switching to a
  Creative Labs Graphics Blaster MA202 solved the problem.  I'm assuming
  the Stealth 64 did something funny with the timings.'


  23.  Copyright

  Copyright (c) 1993-2001 by Andries Brouwer.  This document may be
  distributed under the terms set forth in the LDP license at
  http://metalab.unc.edu/LDP/COPYRIGHT.html or
  ftp://www.win.tue.nl/pub/linux/LDP/COPYRIGHT.txt.

  Additions and corrections are welcome.  Andries Brouwer - aeb@cwi.nl



