Ubuntu Manpage: cu — serial terminal emulator

NAME

       cu — serial terminal emulator

SYNOPSIS

       cu [-dr] [-E escape_char] [-l line] [-s speed | -speed]
       cu [host]

DESCRIPTION

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:

-d Specify that the line is directly connected and cu should not allow the driver to block waiting for
a carrier to be detected.

-E escape_char
Specify an escape character to use instead of the default tilde.

-l 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.

-r Start cu in restricted mode. This prevents all local filesystem operations (~R, ~X, and ~>) and
command executions (~C and ~$).

-s speed | -speed
Set the speed of the connection. The default is 9600.

If host is given, cu uses the remote(5) database to retrieve the dc (directly connected), dv (device) and
br (baud rate) capabilities for that host. The cu utility ignores other capabilities found in that
database.

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:

~^D 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.

~^Z Stop cu (only available with job control).

~C 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

~D Deassert the data terminal ready (DTR) line briefly.

~R 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.

~S Change the speed of the connection.

~X 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.

ENVIRONMENT

       HOST       The default value for host if none is specified via the command line.

       REMOTE     A system description, or an absolute path to a remote(5) system description database.

FILES

       /etc/remote  host description file

EXIT STATUS

       The cu utility exits 0 on success, and >0 if an error occurs.

HISTORY

       The cu command appeared in Version 7 AT&T UNIX.  This version was written for  OpenBSD  5.4  by  Nicholas
       Marriott.

Debian                                          December 12, 2020                                          CU(1)