The Devices That Echo Locally
terminals are one of the things that may perform echoing for a connection. Others include modems, some form of intervening communications processor, or even the host system itself. For several common computer operating systems, it is the host system itself that performs the echoing, if appropriate (which it isn't for, say, entry of a user password when a terminal first connects and a user is prompted to log in). On OpenVMS, for example, echoing is performed as necessary by the host system. Similarly, on Unix-like systems, local echo is performed by the operating system kernel's terminal device driver, according to the state of a device control flag, maintained in software and alterable by applications programs via an ioctl system call. The actual terminals and modems connected to such systems should have their local echo facilities switched off (so that they operate in no echo mode), lest passwords be locally echoed at password prompts, and all other input appear echoed twice. This is as true for terminal emulator programs, such as C-Kermit, running on a computer as it is for real terminals.
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