CU(1) OpenBSD Reference Manual CU(1)NAME
cu - serial terminal emulator
SYNOPSIS
cu [-eho] [-l line] [-s speed | -speed]
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:
-e Use even parity. If both -e and -o are given, then no parity is
used (the default).
-h Echo characters locally (half-duplex mode).
-l line
Specify the line to use. Either of the forms like tty00 or
/dev/tty00 are permitted.
For reasons outlined in tty(4), cua(4) devices should be used on
architectures which have them. For those which do not, tty(4)
devices can be used. Users in group ``dialer'' are permitted to
use cua(4) devices by default; permissions on /dev/tty00 or
/dev/ttya can be changed, but they will revert to their defaults
after an upgrade or (re)install.
-o Use odd parity. If both -e and -o are given, then no parity is
used (the default).
-s speed | -speed
Set the speed of the connection. The default is 9600.
Line access is logged to /var/log/aculog. This file does not exist by
default and has to be created to enable logging.
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.
~c [name] Change directory to name (no argument implies change to
home directory).
~! Escape to a shell (exiting the shell will return to
cu).
~> Copy file from local to remote. cu prompts for the
name of a local file to transmit.
~< Copy file from remote to local. cu prompts first for
the name of the file to be sent, then for a command to
be executed on the remote machine.
~p from [to]
Send a file to a remote UNIX host. This command causes
the remote UNIX system to run the following command
string, sending it the `from' file:
stty -echo; cat > 'to'; stty echo
If the `to' file isn't specified, the `from' file name
is used. This command is actually a UNIX specific
version of the ~> command.
~t from [to]
Take a file from a remote UNIX host. As in the ~p
command, the `to' file defaults to the `from' file name
if it isn't specified. The remote host executes the
following command string to send the file to cu:
cat 'from'; echo '' | tr '\012' '\01'
~| Pipe the output from a remote command to a local UNIX
process. The command string sent to the local UNIX
system is processed by the shell.
~$ 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.
~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
~# Send a BREAK to the remote system. For systems which
don't support the necessary ioctl() call, the break is
simulated by a sequence of line speed changes and DEL
characters.
~s Set a variable (see the discussion below).
~v List all variables and their values (if set).
~^Z Stop cu (only available with job control).
~^Y Stop only the ``local side'' of cu (only available with
job control); the ``remote side'' of cu, the side that
displays output from the remote host, is left running.
~? 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, and by honoring the
locking protocol used by uucico.
During file transfers cu provides a running count of the number of lines
transferred. When using the ~> and ~< commands, the ``eofread'' and
``eofwrite'' variables are used to recognize end-of-file when reading,
and specify end-of-file when writing (see below). File transfers
normally depend on hardwareflow or tandem mode for flow control. If the
remote system does not support hardwareflow or tandem mode, ``echocheck''
may be set to indicate cu should synchronize with the remote system on
the echo of each transmitted character.
VARIABLES
cu maintains a set of variables which control its operation. Some of
these variables are read-only to normal users (root is allowed to change
anything of interest). Variables may be displayed and set through the
`s' escape. The syntax for variables is patterned after vi(1) and
Mail(1). Supplying ``all'' as an argument to the set command displays
all variables readable by the user. Alternatively, the user may request
display of a particular variable by attaching a `?' to the end. For
example, ``escape?'' displays the current escape character.
Variables are numeric, string, character, or boolean values. Boolean
variables are set merely by specifying their name; they may be reset by
prepending a `!' to the name. Other variable types are set by
concatenating an `=' and the value. The entire assignment must not have
any blanks in it. A single set command may be used to interrogate as
well as set a number of variables. Certain common variables have
abbreviations. The following is a list of common variables, their
abbreviations, and their default values:
baudrate (num) The baud rate at which the connection was
established; abbreviated ba.
beautify (bool) Discard unprintable characters when a session is
being scripted; abbreviated be.
echocheck (bool) Synchronize with the remote host during file
transfer by waiting for the echo of the last character
transmitted; default is off.
eofread (str) The set of characters which signify an end-of-
transmission during a ~< file transfer command; abbreviated
eofr.
eofwrite (str) The string sent to indicate end-of-transmission
during a ~> file transfer command; abbreviated eofw.
eol (str) The set of characters which indicate an end-of-line.
cu will recognize escape characters only after an end-of-
line.
escape (char) The command prefix (escape) character; abbreviated
es; default value is `~'.
exceptions (str) The set of characters which should not be discarded
due to the beautification switch; abbreviated ex; default
value is ``\t\n\f\b''.
force (char) The character used to force literal data
transmission; abbreviated fo; default value is `^P'.
framesize (num) The amount of data (in bytes) to buffer between
filesystem writes when receiving files; abbreviated fr.
hardwareflow (bool) Whether hardware flow control (CRTSCTS) is enabled
for the connection; abbreviated hf; default value is `off'.
host (str) The name of the host to which you are connected;
abbreviated ho.
linedisc (num) The line discipline to use; abbreviated ld.
prompt (char) The character which indicates an end-of-line on the
remote host; abbreviated pr; default value is `\n'. This
value is used to synchronize during data transfers. The
count of lines transferred during a file transfer command
is based on receipt of this character.
raise (bool) Upper case mapping mode; abbreviated ra; default
value is off. When this mode is enabled, all lowercase
letters will be mapped to uppercase by cu for transmission
to the remote machine.
raisechar (char) The input character used to toggle uppercase mapping
mode; abbreviated rc; default value is `^A'.
record (str) The name of the file in which a session script is
recorded; abbreviated rec.
script (bool) Session scripting mode; abbreviated sc; default is
off. When script is true, cu will record everything
transmitted by the remote machine in the script record file
specified in record. If the beautify switch is on, only
printable ASCII characters will be included in the script
file (those characters between 040 and 0177). The variable
exceptions is used to indicate characters which are an
exception to the normal beautification rules.
tabexpand (bool) Expand tabs to spaces during file transfers;
abbreviated tab; default value is false. Each tab is
expanded to 8 spaces.
tandem (bool) Use XON/XOFF flow control to throttle data from the
remote host; abbreviated ta. The default value is true.
verbose (bool) Verbose mode; abbreviated verb; default is true.
When verbose mode is enabled, cu shows the current number
of lines transferred during a file transfer operations, and
more.
ENVIRONMENT
HOME The home directory to use for the ~c command.
SHELL The name of the shell to use for the ~! command; default
value is ``/bin/sh''.
FILES
/var/log/aculog line access log
/var/spool/lock/LCK..* lock file to avoid conflicts with uucp
SEE ALSOtip(1)HISTORY
The cu command appeared in 4.2BSD.
BUGS
The full set of variables is undocumented and should, probably, be pared
down.
OpenBSD 4.9 July 22, 2010 OpenBSD 4.9