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 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
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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