PTY(3) FreeBSD Library Functions Manual PTY(3)


openpty, forkptyauxiliary 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 changes 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 invalidates 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.


The openpty() function may fail and set the global variable errno for any of the errors specified for the grantpt(3), posix_openpt(3), ptsname(3), and unlockpt(3) functions and the revoke(2) system call.

In addition to this, forkpty() may set it to any value as described for fork(2).

December 29, 1996 FreeBSD