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OPENPTY(3) Linux Programmer's Manual OPENPTY(3)

NAME

     openpty, login_tty, forkpty - terminal utility functions

SYNOPSIS

     #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.

DESCRIPTION

     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  con-
     trolling  terminal  for the calling process, setting fd to be the stan-
     dard input, output, and error streams of the current process, and clos-
     ing fd.

     The  forkpty() function combines openpty(), fork(2), and login_tty() to
     create a new process operating in a pseudoterminal.  The file  descrip-
     tor  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.

RETURN VALUE

     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.

ERRORS

     openpty() fails if:

     ENOENT There are no available terminals.

     login_tty() fails if ioctl(2) fails to set fd to the controlling termi-
     nal of the calling process.

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

ATTRIBUTES

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

     allbox;  lbw20  lb  lb  l l l.  Interface Attribute Value T{ forkpty(),
     openpty() T}   Thread safety  MT-Safe locale T{ login_tty() T}   Thread
     safety  MT-Unsafe race:ttyname

CONFORMING TO

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

NOTES

     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.

BUGS

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