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TTY(4)											   TTY(4)

       tty - general terminal interface

       #include <sgtty.h>

       This  section  describes  both a particular special file /dev/tty and the terminal drivers
       used for conversational computing.

       Line disciplines.

       The system provides different line disciplines for controlling communications  lines.   In
       this version of the system there are two disciplines available for use with terminals:

       old     The  old (Version 7) terminal driver.  This is sometimes used when using the stan-
	       dard shell sh(1).

       new     The standard Berkeley terminal driver, with features for job control; this must be
	       used when using csh(1).

       Line discipline switching is accomplished with the TIOCSETD ioctl:

	      int ldisc = LDISC;
	      ioctl(f, TIOCSETD, &ldisc);

       where  LDISC  is OTTYDISC for the standard tty driver and NTTYDISC for the ``new'' driver.
       The standard (currently old) tty driver is discipline 0 by convention.  Other  disciplines
       may  exist  for	special purposes, such as use of communications lines for network connec-
       tions.  The current line discipline can be obtained  with  the  TIOCGETD  ioctl.   Pending
       input is discarded when the line discipline is changed.

       All  of	the low-speed asynchronous communications ports can use any of the available line
       disciplines, no matter what hardware is involved.  The remainder of this section discusses
       the "old" and "new" disciplines.

       The control terminal.

       When a terminal file is opened, it causes the process to wait until a connection is estab-
       lished.	In practice, user programs seldom open these files; they are opened  by  getty(8)
       or rlogind(8C) and become a user's standard input and output file.

       If  a process which has no control terminal opens a terminal file, then that terminal file
       becomes the control terminal for that process.  The control terminal is thereafter  inher-
       ited by a child process during a fork(2), even if the control terminal is closed.

       The  file  /dev/tty  is, in each process, a synonym for a control terminal associated with
       that process.  It is useful for programs that wish to be sure of writing messages  on  the
       terminal  no matter how output has been redirected.  It can also be used for programs that
       demand a file name for output, when typed output is desired and it is tiresome to find out
       which terminal is currently in use.

       A  process  can remove the association it has with its controlling terminal by opening the
       file /dev/tty and issuing an

	      ioctl(f, TIOCNOTTY, 0);

       This is often desirable in server processes.

       Process groups.

       Command processors such as csh(1) can arbitrate the terminal  between  different  jobs  by
       placing related jobs in a single process group and associating this process group with the
       terminal.  A terminal's associated process group may be set using the TIOCSPGRP ioctl(2):

	      ioctl(fildes, TIOCSPGRP, &pgrp);

       or examined using TIOCGPGRP, which returns the current process group  in  pgrp.	 The  new
       terminal  driver  aids  in  this arbitration by restricting access to the terminal by pro-
       cesses which are not in the current process group; see Job access control below.


       The terminal drivers have three major modes, characterized by the amount of processing  on
       the input and output characters:

       cooked	 The normal mode.  In this mode lines of input are collected and input editing is
		 done.	The edited line is made available when it is completed by a  newline,  or
		 when  the t_brkc character (normally undefined) or t_eofc character (normally an
		 EOT, control-D, hereafter ^D) is entered.  A carriage	return	is  usually  made
		 synonymous with newline in this mode, and replaced with a newline whenever it is
		 typed.  All driver functions (input editing, interrupt generation,  output  pro-
		 cessing such as tab expansion, etc.)  are available in this mode.

       CBREAK	 This  mode  eliminates  the  character, word, and line editing input facilities,
		 making the input character available to the user program as it is  typed.   Flow
		 control,  literal-next  and  interrupt  processing  are still done in this mode.
		 Output processing is done.

       RAW	 This mode eliminates all input processing and makes all input characters  avail-
		 able as they are typed; no output processing is done either.

       The  style of input processing can also be very different when the terminal is put in non-
       blocking I/O mode; see the FNDELAY flag described in fcntl(2).  In  this  case  a  read(2)
       from the control terminal will never block, but rather return an error indication (EWOULD-
       BLOCK) if there is no input available.

       A process may also request that a SIGIO signal be sent it whenever input  is  present  and
       also whenever output queues fall below the low-water mark.  To enable this mode the FASYNC
       flag should be set using fcntl(2).

       Input editing.

       A UNIX terminal ordinarily operates in full-duplex mode.  Characters may be typed  at  any
       time,  even while output is occurring, and are only lost when the system's character input
       buffers become completely choked, which is rare, or when the user has accumulated the max-
       imum allowed number of input characters that have not yet been read by some program.  Cur-
       rently this limit is 256 characters.  In RAW mode, the terminal	driver	throws	away  all
       input  and  output  without notice when the limit is reached.  In CBREAK or cooked mode it
       refuses to accept any further input and, if in the new line discipline, rings the terminal

       Input  characters  are  normally accepted in either even or odd parity with the parity bit
       being stripped off before the character is given to the program.  By clearing  either  the
       EVEN or ODD bit in the flags word it is possible to have input characters with that parity
       discarded (see the Summary below.)

       In all of the line disciplines, it is possible to simulate terminal input using the  TIOC-
       STI  ioctl,  which  takes,  as its third argument, the address of a character.  The system
       pretends that this character was typed on the argument terminal, which must be the control
       terminal except for the super-user (this call is not in standard version 7 UNIX).

       Input  characters  are  normally echoed by putting them in an output queue as they arrive.
       This may be disabled by clearing the ECHO bit in the flags word using the stty(3C) call or
       the TIOCSETN or TIOCSETP ioctls (see the Summary below).

       In  cooked  mode,  terminal input is processed in units of lines.  A program attempting to
       read will normally be suspended until an entire	line  has  been  received  (but  see  the
       description  of SIGTTIN in Job access control and of FIONREAD in Summary, both below.)  No
       matter how many characters are requested in the read  call,  at	most  one  line  will  be
       returned.  It is not, however, necessary to read a whole line at once; any number of char-
       acters may be requested in a read, even one, without losing information.

       During input, line editing is  normally	done,  with  the  erase  character  sg_erase  (by
       default,  DELETE)  logically  erasing  the  last character typed and the sg_kill character
       (default, ^U: control-U) logically erasing the entire current input line.   These  charac-
       ters never erase beyond the beginning of the current input line or an eof.

       The  drivers normally treat either a carriage return or a newline character as terminating
       an input line, replacing the return with a newline and echoing a return and a  line  feed.
       If the CRMOD bit is cleared in the local mode word then the processing for carriage return
       is disabled, and it is simply echoed as a return,  and  does  not  terminate  cooked  mode

       In  the	new  driver there is a literal-next character (normally ^V) which can be typed in
       both cooked and CBREAK mode preceding any character to prevent its special meaning to  the
       terminal handler.

       The  new  terminal  driver also provides two other editing characters in normal mode.  The
       word-erase character, normally ^W, erases the preceding word, but not  any  spaces  before
       it.  For the purposes of ^W, a word is defined as a sequence of non-blank characters, with
       tabs counted as blanks.	Finally, the reprint character, normally ^R, retypes the  pending
       input beginning on a new line.  Retyping occurs automatically in cooked mode if characters
       which would normally be erased from the screen are fouled by program output.

       Input echoing and redisplay

       The terminal driver has several modes for handling the echoing  of  terminal  input,  con-
       trolled by bits in a local mode word.

       Hardcopy  terminals.   When a hardcopy terminal is in use, the LPRTERA bit is normally set
       in the local mode word.	Characters which are logically erased are then printed out  back-
       wards preceded by `\' and followed by `/' in this mode.

       CRT terminals.  When a CRT terminal is in use, the LCRTBS bit is normally set in the local
       mode word.  The terminal driver then echoes the proper number  of  erase  characters  when
       input is erased; in the normal case where the erase character is a ^H this causes the cur-
       sor of the terminal to back up to where it was before the logically erased  character  was
       typed.	If the input has become fouled due to interspersed asynchronous output, the input
       is automatically retyped.

       Erasing characters from a CRT.  When a CRT terminal is in use, the LCRTERA bit may be  set
       to  cause  input  to be erased from the screen with a "backspace-space-backspace" sequence
       when character or word deleting sequences are used.  A LCRTKIL bit may  be  set	as  well,
       causing the input to be erased in this manner on line kill sequences as well.

       Echoing	of  control  characters.  If the LCTLECH bit is set in the local state word, then
       non-printing (control) characters are normally echoed as ^X (for some X) rather than being
       echoed unmodified; delete is echoed as ^?.

       The  normal  modes for use on CRT terminals are speed dependent.  At speeds less than 1200
       baud, the LCRTERA and LCRTKILL processing is painfully slow,  and  stty(1)  normally  just
       sets  LCRTBS and LCTLECH; at speeds of 1200 baud or greater all of these bits are normally
       set.  Stty(1) summarizes these option settings and the use of the new terminal  driver  as

       Output processing.

       When  one or more characters are written, they are actually transmitted to the terminal as
       soon as previously-written characters have finished typing.  (As noted above, input  char-
       acters  are  normally  echoed by putting them in the output queue as they arrive.)  When a
       process produces characters more rapidly than they can be typed, it will be suspended when
       its  output  queue  exceeds some limit.	When the queue has drained down to some threshold
       the program is resumed.	Even parity is normally generated on output.  The  EOT	character
       is not transmitted in cooked mode to prevent terminals that respond to it from hanging up;
       programs using RAW or CBREAK mode should be careful.

       The terminal drivers provide necessary  processing  for	cooked	and  CBREAK  mode  output
       including  parity  generation.	The  driver will also optionally expand tabs into spaces,
       where the tab stops are assumed to be set every eight columns, and optionally convert new-
       lines  to carriage returns followed by newline.	These functions are controlled by bits in
       the tty flags word; see Summary below.

       Finally, in the new terminal driver, there is a output flush character, normally ^O, which
       sets the LFLUSHO bit in the local mode word, causing subsequent output to be flushed until
       it is cleared by a program or more input is typed.  This  character  has  effect  in  both
       cooked  and  CBREAK  modes  and causes pending input to be retyped if there is any pending
       input.  An ioctl to flush the characters in the input or output queues, TIOCFLUSH, is also

       Flow control.

       There  are  two characters (the stop character, normally ^S, and the start character, nor-
       mally ^Q) which cause output to be suspended and resumed respectively.  Extra stop charac-
       ters  typed when output is already stopped have no effect, unless the start and stop char-
       acters are made the same, in which case output resumes.

       A bit in the flags word may be set to put the terminal into TANDEM mode.  In this mode the
       system  produces  a stop character (default ^S) when the input queue is in danger of over-
       flowing, and a start character (default ^Q) when the input has drained sufficiently.  This
       mode is useful when the terminal is actually another machine that obeys those conventions.

       If  software  flow control is not sufficient (it begins failing above 4800 bits per second
       on slow systems) RTS/CTS flow control is now available.	Hardware flow control causes  RTS
       to  be  dropped	when the remote system (modem) should cease sending and to be raised when
       additional data can be accepted.  If the remote system  drops  CTS  then  the  local  host
       ceases  sending	data  until  the CTS is raised.  Hardware flow control is enabled via the
       TIOCLBIS (or TIOCLBIC or TIOCLSET) function and the bit LRTSCTS.

       Line control and breaks.

       There are several ioctl calls available to control the state of the  terminal  line.   The
       TIOCSBRK  ioctl will set the break bit in the hardware interface causing a break condition
       to exist; this can be cleared (usually after a delay with sleep(3))  by	TIOCCBRK.   Break
       conditions  in the input are reflected as a null character in RAW mode or as the interrupt
       character in cooked or CBREAK mode.  The TIOCCDTR ioctl will clear the data terminal ready
       condition; it can be set again by TIOCSDTR.

       When  the  carrier signal from the dataset drops (usually because the user has hung up his
       terminal) a SIGHUP hangup signal is sent to the processes  in  the  distinguished  process
       group  of  the  terminal;  this	usually causes them to terminate.  The SIGHUP can be sup-
       pressed by setting the LNOHANG bit in the local state word of the driver.  Access  to  the
       terminal  by other processes is then normally revoked, so any further reads will fail, and
       programs that read a terminal and test for  end-of-file	on  their  input  will	terminate

       It  is  possible to ask that the phone line be hung up on the last close with the TIOCHPCL
       ioctl; this is normally done on the outgoing lines and dialups.

       Interrupt characters.

       There are several characters that generate interrupts in cooked and CBREAK mode;  all  are
       sent  to  the processes in the control group of the terminal, as if a TIOCGPGRP ioctl were
       done to get the process group and then a killpg(2) system  call	were  done,  except  that
       these  characters  also	flush  pending	input  and output when typed at a terminal (a`'la
       TIOCFLUSH).  The characters shown here are the defaults; the field names in the structures
       (given below) are also shown.  The characters may be changed.

       ^C     t_intrc  (ETX) generates a SIGINT signal.  This is the normal way to stop a process
	      which is no longer interesting, or to regain control in an interactive program.

       ^\     t_quitc (FS) generates a SIGQUIT signal.	This is used to cause a program to termi-
	      nate  and produce a core image, if possible, in the file core in the current direc-

       ^Z     t_suspc (EM) generates a SIGTSTP signal, which  is  used	to  suspend  the  current
	      process group.

       ^Y     t_dsuspc (SUB) generates a SIGTSTP signal as ^Z does, but the signal is sent when a
	      program attempts to read the ^Y, rather than when it is typed.

       Job access control.

       When using the new terminal driver, if a process which is not in the distinguished process
       group  of  its  control	terminal attempts to read from that terminal its process group is
       sent a SIGTTIN signal.  This signal normally causes the members of that process	group  to
       stop.   If,  however,  the  process is ignoring SIGTTIN, has SIGTTIN blocked, or is in the
       middle of process creation using vfork(2)), the read will return -1 and set errno to EIO.

       When using the new terminal driver with the LTOSTOP bit set in the local modes, a  process
       is  prohibited  from  writing  on  its  control terminal if it is not in the distinguished
       process group for that terminal.  Processes which are holding or ignoring SIGTTOU  signals
       or which are in the middle of a vfork(2) are excepted and allowed to produce output.  Ter-
       minal/window sizes.  In order to accommodate terminals  and  workstations  with	variable-
       sized windows, the terminal driver provides a mechanism for obtaining and setting the cur-
       rent terminal size.  The driver does not use this information internally, but only  stores
       it  and	provides a uniform access mechanism.  When the size is changed, a SIGWINCH signal
       is sent to the terminal's process group so that knowledgeable  programs	may  detect  size
       changes.   This	facility  was added in 4.3BSD and is not available in earlier versions of
       the system.

       Summary of modes.

       Unfortunately, due to the evolution of the terminal driver, there are 4	different  struc-
       tures which contain various portions of the driver data.  The first of these (sgttyb) con-
       tains that part of the information largely common between version 6  and  version  7  UNIX
       systems.  The second contains additional control characters added in version 7.	The third
       is a word of local state added in 4BSD, and the fourth is  another  structure  of  special
       characters  added for the new driver.  In the future a single structure may be made avail-
       able to programs which need to access all this information; most programs need not concern
       themselves with all this state.

       Basic modes: sgtty.

       The basic ioctls use the structure defined in <sgtty.h>:

       struct sgttyb {
	    char sg_ispeed;
	    char sg_ospeed;
	    char sg_erase;
	    char sg_kill;

       The  sg_ispeed  and  sg_ospeed  fields  describe the input and output speeds of the device
       according to the following table, which corresponds to the DEC DH-11 interface.	If  other
       hardware  is used, impossible speed changes are ignored.  Symbolic values in the table are
       as defined in <sgtty.h>.

       B0      0    (hang up dataphone)
       B50     1    50 baud
       B75     2    75 baud
       B110    3    110 baud
       B134    4    134.5 baud
       B150    5    150 baud
       B200    6    200 baud
       B300    7    300 baud
       B600    8    600 baud
       B1200   9    1200 baud
       B1800   10   1800 baud
       B2400   11   2400 baud
       B4800   12   4800 baud
       B9600   13   9600 baud
       EXTA    14   External A
       EXTB    15   External B

       Code conversion and line control required for IBM 2741's (134.5 baud) must be  implemented
       by the user's program.  The half-duplex line discipline required for the 202 dataset (1200
       baud) is not supplied; full-duplex 212 datasets work fine.

       The sg_erase and sg_kill fields of the argument structure specify the erase and kill char-
       acters respectively.  (Defaults are DELETE and ^U.)

       The sg_flags field of the argument structure contains several bits that determine the sys-
       tem's treatment of the terminal:

       XTABS  0004000 Expand tabs on output
       EVENP  0000200 Even parity allowed on input
       ODDP   0000100 Odd parity allowed on input
       RAW    0000040 Raw mode: wake up on all characters, 8-bit interface
       CRMOD  0000020 Map CR into LF; output LF as CR-LF
       ECHO   0000010 Echo (full duplex)
       CBREAK 0000002 Return each character as soon as typed
       TANDEM 0000001 Automatic inbound xon/xoff flow control

       XTABS, causes tabs to be replaced by the appropriate number of spaces on output.

       The flags for even and odd parity control parity checking on input and generation on  out-
       put  in cooked and CBREAK mode (unless LPASS8 is enabled, see below).  Even parity is gen-
       erated on output unless ODDP is set and EVENP is clear, in which case odd parity is gener-
       ated.   Input  characters  with	the  wrong  parity,  as determined by EVENP and ODDP, are
       ignored in cooked and CBREAK mode.

       RAW disables all processing save output flushing with LFLUSHO; full 8 bits  of  input  are
       given  as  soon as it is available; all 8 bits are passed on output.  A break condition in
       the input is reported as a null character.  If the input queue overflows in raw	mode  all
       data  in the input and output queues are discarded; this applies to both new and old driv-

       CRMOD causes input carriage returns to be turned into new-lines,  and  output  and  echoed
       new-lines to be output as a carriage return followed by a line feed.

       CBREAK is a sort of half-cooked (rare?) mode.  Programs can read each character as soon as
       typed, instead of waiting for a full line; all processing is done except the  input  edit-
       ing: character and word erase and line kill, input reprint, and the special treatment of \
       and EOT are disabled.

       TANDEM mode causes the system to produce a stop character (default ^S) whenever the  input
       queue is in danger of overflowing, and a start character (default ^Q) when the input queue
       has drained sufficiently.  It is useful for flow control when  the  `terminal'  is  really
       another computer which understands the conventions.

       Note: The same ``stop'' and ``start'' characters are used for both directions of flow con-
       trol; the t_stopc character is accepted on input as the character that stops output and is
       produced  on output as the character to stop input, and the t_startc character is accepted
       on input as the character that restarts output and is produced on output as the	character
       to restart input.

       Basic ioctls

       A large number of ioctl(2) calls apply to terminals.  Some have the general form:

       #include <sgtty.h>

       ioctl(fildes, code, arg)
       struct sgttyb *arg;

       The applicable codes are:

       TIOCGETP       Fetch  the  basic parameters associated with the terminal, and store in the
		      pointed-to sgttyb structure.

       TIOCSETP       Set the parameters according  to	the  pointed-to  sgttyb  structure.   The
		      interface  delays  until	output	is quiescent, then throws away any unread
		      characters, before changing the modes.

       TIOCSETN       Set the parameters like TIOCSETP but do not delay or flush input.  Input is
		      not preserved, however, when changing to or from RAW.

       With the following codes arg is ignored.

       TIOCEXCL       Set "exclusive-use" mode: no further opens are permitted until the file has
		      been closed.

       TIOCNXCL       Turn off "exclusive-use" mode.

       TIOCHPCL       When the file is closed for the last time, hang up the terminal.	 This  is
		      useful  when  the  line  is  associated  with an ACU used to place outgoing

       With the following codes arg is a pointer to an int.

       TIOCGETD       arg is a pointer to an int into which is placed the current line discipline

       TIOCSETD       arg  is a pointer to an int whose value becomes the current line discipline

       TIOCFLUSH      If the int pointed to by arg has a zero value, all  characters  waiting  in
		      input or output queues are flushed.  Otherwise, the value of the int is for
		      the FREAD and FWRITE bits defined in <sys/file.h>; if the FREAD bit is set,
		      all  characters  waiting in input queues are flushed, and if the FWRITE bit
		      is set, all characters waiting in output queues are flushed.

       The remaining calls are not available in vanilla version 7 UNIX.  In cases where arguments
       are required, they are described; arg should otherwise be given as 0.

       TIOCSTI	      the argument points to a character which the system pretends had been typed
		      on the terminal.

       TIOCSBRK       the break bit is set in the terminal.

       TIOCCBRK       the break bit is cleared.

       TIOCSDTR       data terminal ready is set.

       TIOCCDTR       data terminal ready is cleared.

       TIOCSTOP       output is stopped as if the ``stop'' character had been typed.

       TIOCSTART      output is restarted as if the ``start'' character had been typed.

       TIOCGPGRP      arg is a pointer to an int into which is placed the process group ID of the
		      process group for which this terminal is the control terminal.

       TIOCSPGRP      arg is a pointer to an int which is the value to which the process group ID
		      for this terminal will be set.

       TIOCOUTQ       returns in the int pointed to by arg the number of  characters  queued  for
		      output to the terminal.

       FIONREAD       returns  in the long pointed to by arg the number of characters immediately
		      readable from the argument descriptor.  This works for  files,  pipes,  and


       The  second  structure associated with each terminal specifies characters that are special
       in both the old and new	terminal  interfaces:  The  following  structure  is  defined  in
       <sys/ioctl.h>, which is automatically included in <sgtty.h>:

       struct tchars {
	    char t_intrc;  /* interrupt */
	    char t_quitc;  /* quit */
	    char t_startc; /* start output */
	    char t_stopc;  /* stop output */
	    char t_eofc;   /* end-of-file */
	    char t_brkc;   /* input delimiter (like nl) */

       The default values for these characters are ^C, ^\, ^Q, ^S, ^D, and -1.	A character value
       of -1 eliminates the effect of that character.  The t_brkc character, by default -1,  acts
       like  a	new-line in that it terminates a `line,' is echoed, and is passed to the program.
       The `stop' and `start' characters may be the same, to produce  a  toggle  effect.   It  is
       probably  counterproductive  to	make  other special characters (including erase and kill)
       identical.  The applicable ioctl calls are:

       TIOCGETC    Get the special characters and put them in the specified structure.

       TIOCSETC    Set the special characters to those given in the structure.

       Local mode

       The third structure associated with each terminal is a local mode word.	The bits  of  the
       local mode word are:

       LCRTBS	 000001    Backspace on erase rather than echoing erase
       LPRTERA	 000002    Printing terminal erase mode
       LCRTERA	 000004    Erase character echoes as backspace-space-backspace
       LMDMBUF	 000020    Stop/start output when carrier drops
       LLITOUT	 000040    Suppress output translations
       LTOSTOP	 000100    Send SIGTTOU for background output
       LFLUSHO	 000200    Output is being flushed
       LNOHANG	 000400    Don't send hangup when carrier drops
       LRTSCTS	 001000    RTS/CTS flow control
       LCRTKIL	 002000    BS-space-BS erase entire line on line kill
       LPASS8	 004000    Pass all 8 bits through on input, in any mode
       LCTLECH	 010000    Echo input control chars as ^X, delete as ^?
       LPENDIN	 020000    Retype pending input at next read or input character
       LDECCTQ	 040000    Only ^Q restarts output after ^S, like DEC systems
       LNOFLSH	 100000    Inhibit flushing of pending I/O when an interrupt character is typed.

       The applicable ioctl functions are:

       TIOCLBIS       arg  is a pointer to an int whose value is a mask containing the bits to be
		      set in the local mode word.

       TIOCLBIC       arg is a pointer to an int whose value is a mask containing the bits to  be
		      cleared in the local mode word.

       TIOCLSET       arg is a pointer to an int whose value is stored in the local mode word.

       TIOCLGET       arg  is  a  pointer  to  an  int	into which the current local mode word is

       Local special chars

       The final control structure associated with each terminal is the ltchars  structure  which
       defines control characters for the new terminal driver.	Its structure is:

       struct ltchars {
	    char t_suspc;  /* stop process signal */
	    char t_dsuspc; /* delayed stop process signal */
	    char t_rprntc; /* reprint line */
	    char t_flushc; /* flush output (toggles) */
	    char t_werasc; /* word erase */
	    char t_lnextc; /* literal next character */

       The  default  values  for  these characters are ^Z, ^Y, ^R, ^O, ^W, and ^V.  A value of -1
       disables the character.

       The applicable ioctl functions are:

       TIOCSLTC    arg is a pointer to an ltchars structure which defines the new  local  special

       TIOCGLTC    arg	is a pointer to an ltchars structure into which is placed the current set
		   of local special characters.

       Window/terminal sizes

       Each terminal has provision for storage of the current terminal or window size in  a  win-
       size structure, with format:

       struct winsize {
	    unsigned short    ws_row;	     /* rows, in characters */
	    unsigned short    ws_col;	     /* columns, in characters */
	    unsigned short    ws_xpixel;     /* horizontal size, pixels */
	    unsigned short    ws_ypixel;     /* vertical size, pixels */

       A  value of 0 in any field is interpreted as ``undefined;'' the entire structure is zeroed
       on final close.

       The applicable ioctl functions are:

	      arg is a pointer to a struct winsize into which will be placed the current terminal
	      or window size information.

	      arg is a pointer to a struct winsize which will be used to set the current terminal
	      or window size information.  If the new  information  is	different  than  the  old
	      information, a SIGWINCH signal will be sent to the terminal's process group.


       csh(1), stty(1), tset(1), ioctl(2), sigvec(2), stty(3C), getty(8)

4th Berkeley Distribution		  April 10, 1997				   TTY(4)
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