TTYNAME(3) Library Functions Manual TTYNAME(3)

ttyname, ttyname_r, isatty, ttyslot — get name of associated terminal (tty) from file descriptor

Standard C Library (libc, -lc)

#include <unistd.h>

char *
ttyname(int fd);

int
ttyname_r(int fd, char *buf, size_t len);

int
isatty(int fd);

#include <stdlib.h>

int
ttyslot(void);

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)), or for pseudo-terminal devices created in ptyfs and named /dev/pts/.

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

The () function gets the related device name of a file descriptor for which isatty() is true. The () is the reentrant version of the above, and it places the results in buf. If there is not enough space to place the results (indicated by len), then it returns an error.

The () function fetches the current process' control terminal number from the ttys(5) file entry. If the terminal is a pseudo-terminal, and there is no special entry in the ttys(5) file for it, the slot number returned is 1 + (last slot number) + minor(tty). This will return a consistent and unique number for each pseudo-terminal device without requiring one to enumerate all of them in ttys(5).

As an optimisation, these functions attempt to obtain information about all devices from the /var/run/dev.cdb database, if it exists. If the database exists but is out of date, then these functions may produce incorrect results. The database should be updated using the dev_mkdb(8) command.

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() functions returns 0 on success and an error code on failure.

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.

/dev/∗
 
/etc/ttys
 

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 ttyname_r() function will also fail if:

[]
The terminal device is not found. This can happen if the device node has been removed after it was opened.
[]
The buffer provided is not large enough to fit the result.

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

The ttyname() and isatty() functions conform to IEEE Std 1003.1-1990 (“POSIX.1”).

isatty(), ttyname(), and ttyslot() functions appeared in Version 7 AT&T UNIX.

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.

June 1, 2012 NetBSD 11.0