|File Formats Manual
securetty - list of terminals on which root is allowed to login
The file /etc/securetty contains the names of terminals (one per line, without leading /dev/) which are considered secure for the transmission of certain authentication tokens.
On PAM enabled systems, it is used for the same purpose by pam_securetty(8) to restrict the terminals on which empty passwords are accepted.
|Linux man-pages 6.05.01