NAME
getptmfd, openpty,
fdopenpty, login_tty,
forkpty, fdforkpty —
tty utility functions
SYNOPSIS
#include
<termios.h>
#include <util.h>
int
getptmfd(void);
int
openpty(int
*amaster, int
*aslave, char
*name, const struct
termios *termp, const
struct winsize *winp);
int
fdopenpty(int
ptmfd, int
*amaster, int
*aslave, char
*name, const struct
termios *termp, const
struct winsize *winp);
int
login_tty(int
fd);
pid_t
forkpty(int
*amaster, char
*name, const struct
termios *termp, const
struct winsize *winp);
pid_t
fdforkpty(int
ptmfd, int
*amaster, char
*name, const struct
termios *termp, const
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 allocates the pseudo-tty through the
/dev/ptm device (see
pty(4) for
details) which means that 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
fdopenpty()
and
fdforkpty()
functions work like openpty() and
forkpty() but expect a
/dev/ptm file descriptor ptmfd
obtained from the
getptmfd()
function.
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
getptmfd() may fail and set
errno for any of the errors specified for the routine
open(2).
openpty() and
fdopenpty() will fail if:
- [
ENOENT] - There are no available ttys.
fdopenpty() and
fdforkpty() will fail if
getptmfd() fails. forkpty()
and fdforkpty() will fail if either
openpty() or fork()
fails.
login_tty() will fail if
ioctl() fails to set fd to the
controlling terminal of the current process.