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CU(1) General Commands Manual CU(1)

cu — serial terminal emulator

cu [-l line] [-s speed | -speed]

cu is used to connect to another system over a serial link. In the era before modern networks, it was typically used to connect to a modem in order to dial in to a remote host. It is now frequently used for tasks such as attaching to the serial console of another machine for administrative or debugging purposes.

The options are as follows:

line
Specify the line to use. Either of the forms like cua00 or /dev/cua00 are permitted. The default is /dev/cua00. See cua(4) for information on terminal devices. Users in group “dialer” are permitted to use cua(4) devices by default.
speed | -speed
Set the speed of the connection. The default is 9600.

Typed characters are normally transmitted directly to the remote machine (which does the echoing as well). A tilde (‘~’) appearing as the first character of a line is an escape signal; the following are recognized:

or ~.
Drop the connection and exit. Only the connection is dropped – the login session is not terminated.
Copy file from local to remote. cu prompts for the name of a local file to transmit.
Pipe the output from a local Unix process to the remote host. The command string sent to the local Unix system is processed by the shell.
Send a BREAK to the remote system.
Stop cu (only available with job control).
Fork a child process on the local system to perform special protocols such as XMODEM. The child program will be run with the following arrangement of file descriptors: 
0 <-> remote tty in
1 <-> remote tty out
2 <-> local tty stderr
Deassert the data terminal ready (DTR) line briefly.
Record all output from the remote system to a file. If the given file already exists, it is appended to. If no file is specified, any existing recording is stopped.
Change the speed of the connection.
Send a file with the XMODEM protocol.
Get a summary of the tilde escapes.

When cu prompts for an argument, for example during setup of a file transfer, the line typed may be edited with the standard erase and kill characters. A null line in response to a prompt, or an interrupt, will abort the dialogue and return the user to the remote machine.

cu guards against multiple users connecting to a remote system by opening modems and terminal lines with exclusive access.

The cu command appeared in 4.2BSD. This version was written for OpenBSD 5.4 by Nicholas Marriott.

OpenBSD-5.4 March 11, 2013 CU(1)