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cu(1)
NAME
cu - Connects directly or indirectly to a remote system
SYNOPSIS
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.
STANDARDS
Interfaces documented on this reference page conform to industry standards
as follows:
cu: XPG4, XPG4-UNIX
Refer to the standards(5) reference page for more information about
industry standards and associated tags.
OPTIONS
-d Prints diagnostic traces.
-e Designates that even parity is to be generated for data sent to the
remote system.
-h Emulates local echo, supporting calls to other systems that expect
terminals to be set to half-duplex mode.
-l line
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).
[DIGITAL] 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.)
-n Prompts you to provide the telephone number to be dialed, rather than
taking it from the command line (for added security).
-o Designates that odd parity is to be generated for data sent to the
remote system.
-s speed
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.
-t 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
telephone_number
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.
system
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.
[DIGITAL] 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.
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 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.
[DIGITAL] The system should already be configured to use the cu command.
(See your system administrator for more information.)
[DIGITAL] 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
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).
~!command
Executes the command denoted by command on the local system via sh -c.
~$command
Runs the command denoted by command locally and sends its output to the
remote system for execution.
~%cddirectory
Changes the directory on the local system to directory.
~%take from [to]
Transfers files only. Copies the from file on the remote system to the
to file on the local system. If to is omitted, the remote file is
copied to the local system under the same file name. As each block of
the file is transferred, consecutive single digits are displayed on the
terminal screen.
~%put from [to]
Transfers files only. Copies the from file on the local system to the
to file on the remote system. If to is omitted, the local file is
copied to the remote system under the same file name. As each block of
the file is transferred, consecutive single digits are displayed on the
terminal screen. There is an artificial slowing of transmission by the
cu command during ~%put operations so that loss of data is unlikely.
~~line
Sends the string denoted by ~line to the remote system.
~%break
Transmits a BREAK signal to the remote system. The BREAK can also be
specified as ~%b.
~%debug
[DIGITAL] Toggles the -debug option on or off; this can also be
specified as ~%d.
~t [DIGITAL] Prints the values of the TERMIO structure variables for your
terminal. This is useful for debugging.
~l [DIGITAL] Prints the values of the TERMIO structure variables for the
remote communications line. This is useful for debugging.
~%nostop
Toggles between XON/XOFF input control protocol and no input control.
This is useful in case the remote system is one that does not respond
properly to the <Ctrl-s> and <Ctrl-q> characters.
[DIGITAL] As soon as you enter ~!,~%, ~$, ~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:
SIGHUP
Closes the connection and terminates.
SIGINT
Forwards the signal to the remote system.
SIGQUIT
Forwards the signal to the remote system.
SIGUSR1
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 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
NOTES
1. [DIGITAL] After executing cu, you must log in to the remote system
and press <Return>.
2. [DIGITAL] The cu command does not do integrity checking on data it
transfers.
3. [DIGITAL] Data fields with special cu characters may not be
transmitted properly.
4. [DIGITAL] 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.
5. [DIGITAL] 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:
0 Successful completion.
>0 An error occurred.
EXAMPLES
1. 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.
2. 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.
3. To log in to a system connected by a hardwired asynchronous line,
enter:
cu -l /dev/tty2
4. To dial a remote system with a specified line and a specific speed,
enter:
cu -s 1200 -l tty3
5. To dial a remote system using a specific line associated with a modem,
enter:
cu -l cul4 9=12015551212
6. To open a virtual terminal on the local system after logging in to the
remote system, enter:
~!open sh
7. 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.
8. 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.
9. 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.
10. 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.
11. 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
The following environment variables affect the execution of cu:
LANG
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.
LC_ALL
If set to a non-empty string value, overrides the values of all the
other internationalization variables.
LC_CTYPE
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).
LC_MESSAGES
Determines the locale for the format and contents of diagnostic
messages written to standard error.
NLSPATH
Determines the location of message catalogues for the processing of
LC_MESSAGES.
FILES
/var/spool/locks/LCK..tty_number
Prevents multiple use of device
/usr/lib/uucp/Devices
Information about available devices
/usr/lib/uucp/Dialcodes
Dialing code abbreviations
/usr/lib/uucp/Dialers
Initial handshaking on a link
/usr/lib/uucp/Permissions
Access permission codes
/usr/lib/uucp/Systems
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)