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       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.  If name is not NULL, the buffer it  points  to  is
       used to return the filename of the slave.  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 process.


       openpty() fails if:

       ENOENT There are no available terminals.

       login_tty()  fails  if ioctl(2) fails to set fd to the controlling terminal of the calling

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


       For an explanation of the terms used in this section, see attributes(7).

       │InterfaceAttributeValue                  │
       │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)


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