.\" 
.\" Copyright (c) 1996 Joerg Wunsch
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.Dd December 29, 1996
.Os
.Dt PTY 3
.Sh NAME
.Nm openpty , 
.Nm forkpty
.Nd auxiliary functions to obtain a pseudo-terminal
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <sys/ioctl.h>
.Fd #include <termios.h>
.Fd #include <libutil.h>
.Ft int
.Fn openpty "int *amaster" "int *aslave" "char *name" "struct termios *termp" "struct winsize *winp"
.Ft int
.Fn forkpty "int *amaster" "char *name" "struct termios *termp" "struct winsize *winp"
.Pp
Link with
.Va -lutil
on the
.Xr cc 1
command line.
.Sh DESCRIPTION
The function
.Fn openpty
attempts to obtain the next available pseudo-terminal from the system (see
.Xr pty 4 ) .
If it successfully finds one, it subsequently tries to change the
ownership of the slave device to the real UID of the current process,
the group membership to the group
.Dq tty
(if such a group exists in the system), the access permissions for
reading and writing by the owner, and for writing by the group, and to
invalidate any current use of the line by calling
.Xr revoke 2 .
.Pp
If the argument
.Fa name
is not
.Dv NULL ,
.Fn openpty
copies the pathname of the slave pty to this area.  The caller is
responsible for allocating the required space in this array.
.Pp
If the arguments
.Fa termp
or
.Fa winp
are not
.Dv NULL ,
.Fn openpty
initializes the termios and window size settings from the structures
these arguments point to, respectively.
.Pp
Upon return, the open file descriptors for the master and slave side
of the pty are returned in the locations pointed to by
.Fa amaster
and
.Fa aslave ,
respectively.
.Pp
.Fn Forkpty
first calls
.Fn openpty
to obtain the next available pseudo-terminal from the system.  Upon success,
it forks off a new process.  In the child process, it closes the descriptor
for the master side of the pty, and calls
.Xr login_tty 3
for the slave pty.  In the parent process, it closes the descriptor for the
slave side of the pty.  The arguments
.Fa amaster ,
.Fa name ,
.Fa termp ,
and
.Fa winp
have the same meaning as described for
.Fn openpty .
.Sh RETURN VALUES
.Fn Openpty
returns 0 on success, or -1 on failure.
.Pp
.Fn Forkpty
returns -1 on failure, 0 in the slave process, and the process ID of the
slave process in the parent process.
.Sh ERRORS
On failure,
.Fn openpty
will set the global variable
.Dv errno
to
.Er ENOENT .
.Pp
In addition to this,
.Fn forkpty
may set it to any value as described for
.Xr fork 2 .
.Sh SEE ALSO
.Xr chmod 2 ,
.Xr chown 2 ,
.Xr fork 2 ,
.Xr getuid 2 ,
.Xr open 2 ,
.Xr revoke 2 ,
.Xr login_tty 3 ,
.Xr termios 3 ,
.Xr pty 4 ,
.Xr group 5
.Sh BUGS
The calling process must have an effective UID of super-user in order
to perform all the intended actions.  No notification will occur if
.Fn openpty
or
.Fn forkpty
failed to proceed with one of the described steps, as long as they could
at least allocate the pty at all (and create the new process in the case
of
.Fn forkpty ) .