ttyname, ttyname_r — return name of a terminal


#include <unistd.h>

char *ttyname(int fd);

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


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 appropriately. The function ttyname_r() returns 0 on success, and an error number upon error.



Bad file descriptor.


File descriptor refers to a slave pseudoterminal device but the corresponding pathname could not be found (see Notes).


File descriptor does not refer to a terminal device.


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


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

Conforming to

POSIX.1-2001, POSIX.1-2008, 4.2BSD.


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)


This page is part of release 5.04 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at

Referenced By

ctermid(3), getttyent(3), getutent(3), isatty(3), openpty(3), ptsname(3), sessreg(1), ttyslot(3).

The man page ttyname_r(3) is an alias of ttyname(3).

2019-10-10 Linux Programmer's Manual