openpty, login_tty, forkpty - terminal utility functions


   #include <pty.h>

   int openpty(int *amaster, int *aslave, char *name,
               const struct termios *termp,
               const struct winsize *winp);

   pid_t forkpty(int *amaster, char *name,
                 const struct termios *termp,
                 const struct winsize *winp);

   #include <utmp.h>

   int login_tty(int fd);

   Link with -lutil.


   The  openpty()  function  finds an available pseudoterminal and returns
   file descriptors for the master and slave in amaster  and  aslave.   If
   name  is  not  NULL, the filename of the slave is returned in name.  If
   termp is not NULL, the terminal parameters of the slave will be set  to
   the values in termp.  If winp is not NULL, the window size of the slave
   will be set to the values in winp.

   The login_tty() function prepares for a login on the terminal fd (which
   may  be  a  real  terminal  device, or the slave of a pseudoterminal as
   returned by openpty())  by  creating  a  new  session,  making  fd  the
   controlling  terminal  for  the  calling  process, setting fd to be the
   standard input, output, and error streams of the current  process,  and
   closing fd.

   The  forkpty() function combines openpty(), fork(2), and login_tty() to
   create  a  new  process  operating  in  a  pseudoterminal.   The   file
   descriptor  of  the  master  side  of the pseudoterminal is returned in
   amaster, and the filename of the slave in name if it is not NULL.   The
   termp  and  winp  arguments,  if  not NULL, will determine the terminal
   attributes and window size of the slave side of the pseudoterminal.


   If a call to openpty(), login_tty(), or forkpty() is not successful, -1
   is  returned  and  errno  is  set  to  indicate  the error.  Otherwise,
   openpty(), login_tty(), and the child process of  forkpty()  return  0,
   and the parent process of forkpty() returns the process ID of the child


   openpty() will fail if:

   ENOENT There are no available terminals.

   login_tty() will fail if ioctl(2) fails to set fd  to  the  controlling
   terminal of the calling process.

   forkpty() will fail if either openpty() or fork(2) fails.


   For   an   explanation   of   the  terms  used  in  this  section,  see

   Interface             Attribute      Value                  
   forkpty(), openpty()  Thread safety  MT-Safe locale         
   login_tty()           Thread safety  MT-Unsafe race:ttyname 


   These are BSD functions, present in glibc.  They are  not  standardized
   in POSIX.


   The  const  modifiers  were added to the structure pointer arguments of
   openpty() and forkpty() in glibc 2.8.

   In versions of glibc before 2.0.92, openpty() returns file  descriptors
   for a BSD pseudoterminal pair; since glibc 2.0.92, it first attempts to
   open a UNIX 98 pseudoterminal pair, and falls back  to  opening  a  BSD
   pseudoterminal pair if that fails.


   Nobody  knows  how much space should be reserved for name.  So, calling
   openpty() or forkpty() with non-NULL name may not be secure.


   fork(2), ttyname(3), pty(7)


   This page is part of release 4.09 of the Linux  man-pages  project.   A
   description  of  the project, information about reporting bugs, and the
   latest    version    of    this    page,    can     be     found     at


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