ttyname, ttyname_r - return name of a terminal
The function ttyname() returns a pointer to the
null-terminated pathname of the terminal device that is open on the file
fd, or NULL on error (for example, if
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
Bad file descriptor.
fd refers to a slave pseudoterminal device but the
corresponding pathname could not be found (see NOTES).
fd does not refer to a terminal device.
buflen was too small to allow
storing the pathname.
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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