cu - Connects directly or indirectly to a remote system
cu [-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 capabilities, such as file transfer.
Interfaces documented on this reference page conform to
industry standards as follows:
cu: XCU5.0
Refer to the standards(5) reference page for more information
about industry standards and associated tags.
Prints diagnostic traces. Designates that even parity is
to be generated for data sent to the remote system. Emulates
local echo, supporting 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 administrator for
more information.) Prompts you to provide the
telephone number to be dialed, rather than taking
it from the command 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) transmission 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 autoanswer.
Appropriate mapping of carriage-return to
carriage-return/linefeed pairs is set.
When using a modem, the argument is the telephone number,
with appropriately placed equal signs for secondary dial
tones, or dashes for delays of 4 seconds. The name of the
remote system with which a connection is established. A
system name can be used rather than a telephone 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 specified line
and speed.
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 commands 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
systems.
Local Tilde Commands [Toc] [Back]
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 artificial slowing of transmission by the cu
command during ~%put operations 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 values 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 <Ctrlq>
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 [Toc] [Back]
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 [Toc] [Back]
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 example, 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
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 interconnection 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.
The following exit values are returned: Successful completion.
An error occurred.
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 system 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 system (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 [Toc] [Back] The following environment variables affect the execution
of cu: Provides 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 variables contain
an invalid setting, the utility behaves as if none of
the variables had been defined. If set to a non-empty
string value, overrides 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 multibyte
characters in arguments). Determines the locale for the
format and contents of diagnostic messages written to
standard error. Determines the location of message catalogues
for the processing of LC_MESSAGES.
Prevents multiple use of device Information about available
devices Dialing code abbreviations Initial handshaking
on a link Access permission codes Accessible remote
systems
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)
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