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cu(1) General Commands Manual 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 capabili- ties, such as file transfer. STANDARDS Interfaces documented on this reference page conform to industry stan- dards as follows: cu: XPG4, XPG4-UNIX Refer to the standards(5) reference page for more information about in- dustry 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-du- plex 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). [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.) 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 appro- priate 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 interfer- ence on the line. Used to dial a terminal that has been set to auto-answer. Appropriate mapping of carriage-return to car- riage-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 de- lays of 4 seconds. The name of the remote system with which a connec- tion is established. A system name can be used rather than a telephone number; in that case, cu obtains an appropriate hardwired line or tele- phone 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 avail- able 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 com- mands on either one without dropping the communications link. If the remote computer is also running the proper software (see Additional In- formation), you can transfer files between the two systems. [DIGITAL] The system should already be configured to use the cu com- mand. (See your system administrator for more information.) [DIGITAL] After issuing cu from the local system, you must press <Re- turn> 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 re- mote 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 com- mand denoted by command on the local system via sh -c. Runs the com- mand denoted by command locally and sends its output to the remote sys- tem for execution. Changes the directory on the local system to direc- tory. 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 omit- ted, 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. [DIGITAL] Toggles the -debug op- tion on or off; this can also be specified as ~%d. [DIGITAL] Prints the values of the TERMIO structure variables for your terminal. This is useful for debugging. [DIGITAL] 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. [DIGITAL] As soon as you enter ~!,~%, ~$, ~t, or ~l, the system dis- plays the name of the local computer in the a format such as the fol- lowing: ~[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 se- quence. 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 re- mote 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 lo- cal 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 [DIGITAL] After executing cu, you must log in to the remote system and press <Return>. [DIGITAL] The cu command does not do integrity check- ing on data it transfers. [DIGITAL] Data fields with special cu char- acters may not be transmitted properly. [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. [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: Successful completion. An er- ror 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, en- ter: 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, en- ter: 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 re- mote 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. De- termines 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 Di- aling 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)