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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 referred to by the file
       descriptor 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.  A file descriptor referring to 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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