NAME
openpty,
login_tty, forkpty —
tty utility functions
SYNOPSIS
#include
<termios.h>
#include <util.h>
int
openpty(int
*amaster, int
*aslave, char
*name, struct termios
*termp, struct winsize
*winp);
int
login_tty(int
fd);
pid_t
forkpty(int
*amaster, char
*name, struct termios
*termp, struct winsize
*winp);
DESCRIPTION
The
openpty(),
login_tty(), and forkpty()
functions perform manipulations 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 parameters of the slave will be set to the values in
termp. If winp is non-null, the
window size of the slave will be set to the values in
winp.
The
openpty()
function works in the following way: first it attempts to 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 by iterating through all existing pseudo-tty devices in
/dev. When a free pseudo-tty is found, its ownership
is changed to the UID of the caller, permissions 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 cases.
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
openpty()) 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 login_tty() to create a new process operating in
a pseudo-tty. The file descriptor of 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 winp parameters, if
non-null, will determine the terminal attributes and window size of the
slave side of the pseudo-tty.
RETURN VALUES
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.
FILES
- /dev/pty[p-zP-T][0-9a-zA-Z]
- master pseudo terminals
- /dev/tty[p-zP-T][0-9a-zA-Z]
- slave pseudo terminals
- /dev/ptm
- pseudo terminal management device
ERRORS
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
openpty() or fork()
fails.