The argument tty is the special device file in /dev to open for the terminal (for example, ``ttyh0''). If there is no argument or the argument is `- ' the tty line is assumed to be open as file descriptor 0.
The type argument can be used to make treat the terminal line specially. This argument is used as an index into the gettytab(5) database, to determine the characteristics of the line. If there is no argument, or there is no such table, the default table is used. If there is no /etc/gettytab a set of system defaults is used. If indicated by the table located, will clear the terminal screen, print a banner heading, and prompt for a login name. Usually either the banner or the login prompt will include the system hostname.
Most of the default actions of can be circumvented, or modified, by a suitable gettytab table.
A terminal which is turned on in the ttys file cannot be opened, likely because the requisite lines are either not configured into the system, the associated device was not attached during boot-time system configuration, or the special file in /dev does not exist.