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
command connects one system to a remote system.
If the remote system is running the proper software,
provides additional capabilities, such as file transfer.
Interfaces documented on this reference page conform to industry standards as follows:
cu: XPG4, XPG4-UNIX
Refer to the
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 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.
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.
[Compaq] The system should already be configured to use the cu command. (See your system administrator for more information.)
[Compaq] 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
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
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. [Compaq] Toggles the -debug option on or off; this can also be specified as ~%d. [Compaq] Prints the values of the TERMIO structure variables for your terminal. This is useful for debugging. [Compaq] 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 <Ctrl-q> characters.
[Compaq] 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:
You then enter the command to be executed on the local computer.
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.
process without the normal
connection closing sequence.
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 ~>.
[Compaq] After executing
cu, you must
log in to the remote system and press
command does not do integrity
checking on data it transfers.
[Compaq] Data fields with special
may not be transmitted properly.
[Compaq] 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.
[Compaq] There is an artificial slowing of transmission by
operation so that loss
of data is unlikely.
The following exit values are returned:
An error occurred.
To connect to a remote system using a system name, enter: cu venus
The following environment variables affect the execution of
Provides a default value for the internationalization variables
that are unset or null. If
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
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)