cu(1)cu(1)NAMEcu - Connects directly or indirectly to a remote system
SYNOPSIScu [-dht] [-e | -o] [-l line] [-s speed] -n | telephone_number
cu [-dhnt] [-e | -o] system
The cu command connects one system to a remote system. If the remote
system is running the proper software, cu provides additional capabili‐
ties, such as file transfer.
STANDARDS
Interfaces documented on this reference page conform to industry stan‐
dards as follows:
cu: XCU5.0
Refer to the standards(5) reference page for more information about
industry standards and associated tags.
OPTIONS
Prints diagnostic traces. Designates that even parity is to be gener‐
ated for data sent to the remote system. Emulates local echo, support‐
ing calls to other systems that expect terminals to be set to half-
duplex mode. Specifies a device name to use as the communications
line. This can be used to override the search that would otherwise
take place for the first available line with the right speed. When the
-l option is used without the -s option, the speed of a line is taken
from the /usr/lib/uucp/Devices file.
When the -l and -s options are used together, cu searches the
/usr/lib/uucp/Devices file to check whether the requested speed
is available for the specified line. If so, the connection is
made at the requested speed; otherwise, an error message is
printed, and the call is not made.
The specified device is generally a hardwired asynchronous line
(for example, /dev/tty2), in which case a telephone number
(telephone_number) is not required. If the specified device is
associated with a modem, a telephone number must be provided.
Using this option with system rather than with telephone_number
does not give the desired result (see system, which follows).
[Tru64 UNIX] Under ordinary circumstances, you should not have
to specify the transmission speed, or a line/device. The
default values should be sufficient. (See your system adminis‐
trator for more information.) Prompts you to provide the tele‐
phone number to be dialed, rather than taking it from the com‐
mand line (for added security). Designates that odd parity is
to be generated for data sent to the remote system. Specifies
the transmission speed (300, 1200, 2400, 4800, or 9600 baud).
The default value is Any speed, which instructs the system to
use the rate appropriate for the default (or specified) trans‐
mission line. (The order of the transmission lines is specified
in the /usr/lib/uucp/Devices file.) Most modems operate at 300,
1200, or 2400 baud, while most hardwired lines are set to 1200
baud or higher. When transferring data such as a file between a
local and a remote system, a speed of 300 baud may occasionally
need to be specified. The lower baud rate results in less
interference on the line. Used to dial a terminal that has been
set to auto-answer. Appropriate mapping of carriage-return to
carriage-return/linefeed pairs is set.
OPERANDS
When using a modem, the argument is the telephone number, with appro‐
priately placed equal signs for secondary dial tones, or dashes for
delays of 4 seconds. The name of the remote system with which a con‐
nection is established. A system name can be used rather than a tele‐
phone number; in that case, cu obtains an appropriate hardwired line or
telephone number from /usr/lib/uucp/Systems. System names must be
ASCII characters only.
[Tru64 UNIX] Do not use the system operand in conjunction with
the -l and -s options. If you do, cu connects to the first
available line for the requested system name, ignoring the spec‐
ified line and speed.
DESCRIPTION
The cu command can establish the connection over a hardwired line, or
over a telephone line via a modem. Once the connection is established,
you can be logged in on both systems at the same time, executing com‐
mands on either one without dropping the communications link. If the
remote computer is also running the proper software (see Additional
Information), you can transfer files between the two systems.
[Tru64 UNIX] The system should already be configured to use the cu
command. (See your system administrator for more information.)
[Tru64 UNIX] After issuing cu from the local system, you must press
<Return> and then log in to the remote system.
After making the connection, cu runs as two concurrent processes: the
transmit process reads data from standard input and, except for lines
beginning with a ~ (tilde), passes that data to the remote terminal.
The receive process accepts data from the remote system and, except for
lines beginning with a ~ (tilde), passes it to standard output. To
control input from the remote system so the buffer is not overrun, cu
uses an automatic XON/XOFF protocol.
In addition to issuing regular system commands on the remote system,
you can also issue special cu local commands, which are preceded by a ~
(tilde). Use these ~ commands to issue system commands on the local
system and to perform tasks such as transferring files between two sys‐
tems.
Local Tilde Commands
The transmit process interprets lines beginning with a tilde in the
following ways: Logs you off the remote computer and terminates the
remote connection. Depending on the interconnection hardware, it may
be necessary to use a ~. to terminate the conversation even if the
normal log off sequence was used. Returns you to an interactive shell
on the local system. Toggle between the local and remote systems using
~! (remote to local) and End-of-File (local to remote). Executes the
command denoted by command on the local system via sh -c. Runs the
command denoted by command locally and sends its output to the remote
system for execution. Changes the directory on the local system to
directory. Transfers files only. Copies the from file on the remote
system to the to file on the local system. If to is omitted, the
remote file is copied to the local system under the same file name. As
each block of the file is transferred, consecutive single digits are
displayed on the terminal screen. Transfers files only. Copies the
from file on the local system to the to file on the remote system. If
to is omitted, the local file is copied to the remote system under the
same file name. As each block of the file is transferred, consecutive
single digits are displayed on the terminal screen. There is an arti‐
ficial slowing of transmission by the cu command during ~%put opera‐
tions so that loss of data is unlikely. Sends the string denoted by
~line to the remote system. Transmits a BREAK signal to the remote
system. The BREAK can also be specified as ~%b. [Tru64 UNIX] Toggles
the -debug option on or off; this can also be specified as ~%d. [Tru64
UNIX] Prints the values of the TERMIO structure variables for your
terminal. This is useful for debugging. [Tru64 UNIX] Prints the val‐
ues of the TERMIO structure variables for the remote communications
line. This is useful for debugging. Toggles between XON/XOFF input
control protocol and no input control. This is useful in case the
remote system is one that does not respond properly to the <Ctrl-s> and
<Ctrl-q> characters.
[Tru64 UNIX] As soon as you enter ~!,~%, ~$, ~t, or ~l, the system
displays the name of the local computer in the a format such as the
following:
~[system]!/%
You then enter the command to be executed on the local computer.
Asynchronous Events
The cu command takes the default action upon receipt of signals, with
the exception of: Closes the connection and terminates. Forwards the
signal to the remote system. Forwards the signal to the remote system.
Terminates the cu process without the normal connection closing
sequence.
Additional Information
The receive process normally copies data from the remote system to the
local system's standard output. Internally, the program accomplishes
this by initiating an output diversion to a file when a line from the
remote system begins with ~>.
Data from the remote system is diverted to file on the local
system. The trailing ~> marks the end of the diversion. The use
of ~%put requires stty and cat on the remote system. It also
requires that the current Erase and Kill characters on the
remote system be identical to these current control characters
on the local system. Backslashes are inserted at appropriate
places. The use of ~%take requires echo and cat on the remote
system. Also, stty tabs mode should be set on the remote system
if tabs are to be copied without expansion to spaces. The cu
command can be used to connect multiple systems, and commands
can then be executed on any of the connected systems. For exam‐
ple, issue cu on system X to connect to system Y, and then issue
cu on system Y to connect to system Z. System X is then the
local computer, and systems Y and Z are remote computers.
You can execute commands on system Z by logging in and issuing
the command. Commands can be executed on system X by prefixing
the command with a single tilde (~command), and on system Y by
prefixing the command with two tildes (~~command). In general,
one tilde causes the specified command to be executed on the
original local computer, and two tildes cause the command to be
executed on the next system on which cu was issued.
For example, once the multiple systems are connected, you can
execute the uname command with the -n option (to display the
node name) on Z, X, and Y as follows: $ uname -n Z
$ ~!uname -n X
$ ~~!uname -n Y
NOTES
The cu utility is marked LEGACY in XCU Issue 5. [Tru64 UNIX] After
executing cu, you must log in to the remote system and press <Return>.
[Tru64 UNIX] The cu command does not do integrity checking on data it
transfers. [Tru64 UNIX] Data fields with special cu characters may
not be transmitted properly. [Tru64 UNIX] Depending on the intercon‐
nection hardware, it may be necessary to use a ~. (tilde) to terminate
the conversation, even if the normal logout sequence was used. [Tru64
UNIX] There is an artificial slowing of transmission by cu5 during the
~%put operation so that loss of data is unlikely.
EXIT STATUS
The following exit values are returned: Successful completion. An
error occurred.
EXAMPLES
To connect to a remote system using a system name, enter: cu venus
In this example, you are connected to the remote system venus,
which is listed in the file /usr/lib/uucp/Systems. To dial a
remote system whose telephone number is 1-201-555-1212, where
dialing 9 is required to get an outside dial tone and the baud
rate is 1200, enter: cu-s 1200 9=12015551212
If the speed is not specified, Any is the default value. To log
in to a system connected by a hardwired asynchronous line,
enter: cu-l /dev/tty2 To dial a remote system with a specified
line and a specific speed, enter: cu-s 1200 -l tty3 To dial a
remote system using a specific line associated with a modem,
enter: cu-l cul4 9=12015551212 To open a virtual terminal on
the local system after logging in to the remote system, enter:
~!open sh To display the contents of a file after logging in to
the remote system, enter: ~!more /usr/msg/memos/file10
The contents of file10 in the directory /usr/msg/memos on the
local system are displayed. To copy a file from the local sys‐
tem to the remote system (after logging in to the remote system)
without changing the file name, enter: ~%put /u/judith/file
The file /u/judith/file is copied from the local system to the
remote system without changing the name of the file. To copy a
file from the local system to the remote system (after logging
in to the remote system) and change the file name, enter: ~%put
/u/judith/file /u/judith/tmpfile
The file /u/judith/file is copied from the local to the remote
system and renamed /u/judith/tmpfile. To copy a file from the
remote system to the local system (after logging in to the
remote system) without changing the name of the file, enter:
~%take /u/jeanne/test1
The file /u/jeanne/test1 is copied from the remote to the local
system. To copy a file from the remote system to the local sys‐
tem (after logging in to the remote system) and change the file
name, enter: ~%take /u/jeanne/test1 /u/jeanne/tmptest
The file /u/jeanne/test1 is copied from the remote to the local
system and renamed /u/jeanne/tmptest.
ENVIRONMENT VARIABLES
The following environment variables affect the execution of cu: Pro‐
vides a default value for the internationalization variables that are
unset or null. If LANG is unset or null, the corresponding value from
the default locale is used. If any of the internationalization vari‐
ables contain an invalid setting, the utility behaves as if none of the
variables had been defined. If set to a non-empty string value, over‐
rides the values of all the other internationalization variables.
Determines the locale for the interpretation of sequences of bytes of
text data as characters (for example, single-byte as opposed to multi‐
byte characters in arguments). Determines the locale for the format
and contents of diagnostic messages written to standard error. Deter‐
mines the location of message catalogues for the processing of LC_MES‐
SAGES.
FILES
Prevents multiple use of device Information about available devices
Dialing code abbreviations Initial handshaking on a link Access permis‐
sion codes Accessible remote systems
SEE ALSO
Commands: cat(1), ct(1), echo(1), rmail(1), stty(1), tip(1), uname(1),
uucico(8), uucleanup(8), uucp(1), uuencode(1), uudecode(1), uulog(1),
uuname(1), uupick(1), uusched(8), uusend(1), uustat(1), uuto(1), uux(1)
Standards: standards(5)cu(1)
