openpty, login_tty, forkpty - tty utility functions
openpty(int *amaster, int *aslave, char *name, struct
struct winsize *winp);
forkpty(int *amaster, char *name, struct termios *termp,
struct winsize *winp);
The openpty(), login_tty(), and forkpty() functions perform
on ttys and pseudo-ttys.
The openpty() function finds an available pseudo-tty and returns file descriptors
for the master and slave in amaster and aslave.
If name is
non-null, the filename of the slave is returned in name (a
string of at
least 16 characters). If termp is non-null, the terminal
the slave will be set to the values in termp. If winp is
window size of the slave will be set to the values in winp.
The openpty() function works in the following way: first it
allocate the pseudo-tty through the /dev/ptm device (see
pty(4) for details)
and if that fails it searches for a free pseudo-tty
through all existing pseudo-tty devices in /dev. When a
is found, its ownership is changed to the UID of the caller,
are set to correct values, and all earlier uses of that device are revoked
(see revoke(2) for details). The first method can
work for any user,
the second method requires super-user privileges in most
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-tty as returned
by creating a new session, making fd the controlling terminal for the
current 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(), and
create a new process operating in a pseudo-tty. The file
the master side of the pseudo-tty is returned in amaster,
and the filename
of the slave in name if it is non-null. The termp and
if non-null, will determine the terminal attributes
and window size
of the slave side of the pseudo-tty.
If a call to openpty(), login_tty(), or forkpty() is not
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() will fail if:
[ENOENT] There are no available ttys.
login_tty() will fail if ioctl() fails to set fd to the controlling terminal
of the current process. forkpty() will fail if either
fork(2), revoke(2), pty(4)
OpenBSD 3.6 November 4, 1996
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