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       openpty, login_tty, forkpty - tty utility functions


       #include <pty.h>

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

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

       #include <utmp.h>

       int login_tty(int fd);

       Link with -lutil.


       The  openpty()  function finds an available pseudo-terminal 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 tty fd (which  may
       be  a real tty device, or the slave of a pseudo-terminal 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  pseudo-terminal.   The  file
       descriptor of the master side of the  pseudo-terminal  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 pseudo-terminal.


       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 ttys.

       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.


       These are BSD functions, present in libc5 and glibc2.


       In versions of glibc before 2.0.92, openpty() returns file  descriptors
       for  a  BSD pseudo-terminal pair; since glibc 2.0.92, it first attempts
       to open a Unix 98 pseudo-terminal pair, and falls back to opening a BSD
       pseudo-terminal 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)


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