PTY(3) BSD Library Functions Manual PTY(3)


openpty, forkpty — auxiliary functions to obtain a pseudo-terminal


System Utilities Library (libutil, −lutil)


#include <sys/types.h>
#include <sys/ioctl.h>
#include <termios.h>
#include <libutil.h>


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, respectively.

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 fork(2).


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()).

BSD December 29, 1996 BSD