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TTYNAME(3) Library Functions Manual TTYNAME(3)

ttyname, ttyname_r, isatty, ttyslotget name of associated terminal (tty) from file descriptor

#include <unistd.h>

char *
ttyname(int fd);

ttyname_r(int fd, char *name, size_t namesize);

isatty(int fd);

#include <stdlib.h>


These functions operate on the system file descriptors for terminal type devices. These descriptors are not related to the standard I/O FILE typedef, but refer to the special device files found in /dev and named /dev/tty and for which an entry exists in the initialization file /etc/ttys (see ttys(5)).

The () function determines if the file descriptor fd refers to a valid terminal type device.

The () and () functions get the related device name of a file descriptor for which isatty() is true. The ttyname_r() function stores the NUL-terminated pathname of the terminal associated with the file descriptor fd in the character array referenced by name. The array is namesize characters long and should have space for the name and the terminating NUL character. The maximum length of the terminal name is TTY_NAME_MAX.

The () function fetches the current process's control terminal number from the ttys(5) file entry.

The ttyname() function returns the NUL-terminated name if the device is found and isatty() is true; otherwise a null pointer is returned and errno is set to indicate the error.

The ttyname_r() function returns zero if successful; otherwise an error number is returned.

The isatty() function returns 1 if fd is associated with a terminal device; otherwise it returns 0 and errno is set to indicate the error.

The ttyslot() function returns the unit number of the device file if found; otherwise the value zero is returned.


The ttyname(), ttyname_r(), and isatty() functions will fail if:

The fd argument is not a valid file descriptor.
The fd argument does not refer to a terminal device.
The value of namesize is smaller than the length of the string to be returned including the terminating NUL character.

ioctl(2), ttys(5), dev_mkdb(8)

The isatty(), ttyname(), and ttyslot() functions appeared in Version 7 AT&T UNIX. The ttyname_r() function appeared in the POSIX Threads Extension (1003.1c-1995).

The ttyname() function leaves its result in an internal static object and returns a pointer to that object. Subsequent calls to ttyname() will modify the same object.

November 12, 2013 OpenBSD-6.8