cu ("call Unix") is a Unix utility for establishing a connection between two computer systems via a serial port to another computer system.
Now that intersystem communications are much more easily and reliably handled via Internet connections, its more typical use is to establish a terminal connection to another system via a modem or direct cabling.
[1] It was originally released as part of the 4.2BSD Unix operating system in 1983.
In the same year, it was one of several UNIX tools available for Charles River Data Systems' UNOS operating system under Bell Laboratories license.
[3][4] cu [-v] [--speed