openpty, forkpty -- auxiliary functions to obtain a pseudo-terminal
System Utilities Library (libutil, -lutil)
openpty(int *amaster, int *aslave, char *name, struct termios *termp,
struct winsize *winp);
forkpty(int *amaster, char *name, struct termios *termp,
struct winsize *winp);
The function openpty() attempts to obtain the next available pseudo-terminal
from the system (see 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
``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 revoke(2).
If the argument name is not NULL, openpty() copies the pathname of the
slave pty to this area. The caller is responsible for allocating the
required space in this array.
If the arguments termp or winp are not NULL, openpty() initializes the
termios and window size settings from the structures these arguments
point to, respectively.
Upon return, the open file descriptors for the master and slave side of
the pty are returned in the locations pointed to by amaster and aslave,
The forkpty() function first calls 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 login_tty(3) for the slave pty. In the parent
process, it closes the descriptor for the slave side of the pty. The
arguments amaster, name, termp, and winp have the same meaning as
described for openpty().
The openpty() function returns 0 on success, or -1 on failure.
The forkpty() function returns -1 on failure, 0 in the slave process, and
the process ID of the slave process in the parent process.
On failure, openpty() will set the global variable errno to ENOENT.
In addition to this, forkpty() may set it to any value as described for
chmod(2), chown(2), fork(2), getuid(2), open(2), revoke(2), login_tty(3),
pty(4), termios(4), group(5)
The calling process must have an effective UID of super-user in order to
perform all the intended actions. No notification will occur if
openpty() or 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 forkpty()).
FreeBSD 5.2.1 December 29, 1996 FreeBSD 5.2.1 [ Back ]