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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.
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.
EBADF Bad file descriptor. ENOTTY File descriptor does not refer to a terminal device. ERANGE (ttyname_r()) buflen was too small to allow storing the pathname. ENODEV File descriptor refers to a slave pseudoterminal device but the corresponding pathname could not be found (see NOTES).
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 │ └────────────┴───────────────┴────────────────────────┘
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.
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