or, what it should be: Not a terminal
One of the more obscure error messages that Unix generates :) They were expecting to have a terminal (TTY), but instead got passed something else (a file, a pipe, a socket or something). This often occurs in shell scripts that want to use stty(1) to configure the terminal, but are being run from crond(8)? or perhaps your .profile when you're logging in using something that doesn't create a terminal (eg: issuing a remote command using ssh(1)).
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