ttyname(3)                 Library Functions Manual                 ttyname(3)

NAME
       ttyname, ttyname_r - return name of a terminal

LIBRARY
       Standard C library (libc, -lc)

SYNOPSIS
       #include <unistd.h>

       char *ttyname(int fd);
       int ttyname_r(int fd, char buf[.buflen], size_t buflen);

DESCRIPTION
       The function ttyname() returns a pointer to the null-terminated
       pathname of the terminal device that is open on the file descriptor fd,
       or NULL on error (for example, if fd is not connected to a terminal).
       The return value may point to static data, possibly overwritten by the
       next call.  The function ttyname_r() stores this pathname in the buffer
       buf of length buflen.

RETURN VALUE
       The function ttyname() returns a pointer to a pathname on success.  On
       error, NULL is returned, and errno is set to indicate the error.  The
       function ttyname_r() returns 0 on success, and an error number upon
       error.

ERRORS
       EBADF  Bad file descriptor.

       ENODEV fd refers to a slave pseudoterminal device but the corresponding
              pathname could not be found (see NOTES).

       ENOTTY fd does not refer to a terminal device.

       ERANGE (ttyname_r()) buflen was too small to allow storing the
              pathname.

ATTRIBUTES
       For an explanation of the terms used in this section, see
       attributes(7).

       +-----------------------------+---------------+------------------------+
       |Interface                    | Attribute     | Value                  |
       +-----------------------------+---------------+------------------------+
       |ttyname ()                   | Thread safety | MT-Unsafe race:ttyname |
       +-----------------------------+---------------+------------------------+
       |ttyname_r ()                 | Thread safety | MT-Safe                |
       +-----------------------------+---------------+------------------------+
STANDARDS
       POSIX.1-2008.

HISTORY
       POSIX.1-2001, 4.2BSD.

NOTES
       A process that keeps a file descriptor that refers to a pts(4) device
       open when switching to another mount namespace that uses a different
       /dev/ptmx instance may still accidentally find that a device path of
       the same name for that file descriptor exists.  However, this device
       path refers to a different device and thus can't be used to access the
       device that the file descriptor refers to.  Calling ttyname() or
       ttyname_r() on the file descriptor in the new mount namespace will
       cause these functions to return NULL and set errno to ENODEV.

SEE ALSO
       tty(1), fstat(2), ctermid(3), isatty(3), pts(4)

Linux man-pages 6.7               2023-10-31                        ttyname(3)