Communication Commands cu(1C)
NAME
cu - call another UNIX system
SYNOPSIS
cu [-c device | -l line] [-s speed] [-b bits] [-h] [-n]
[-t] [-d] [-o | -e] [-L] [-C] [-H] telno | systemname
[local-cmd]
DESCRIPTION
The command cu calls up another UNIX system, a terminal, or
possibly a non-UNIX system. It manages an interactive
conversation with possible transfers of files. It is con-
venient to think of cu as operating in two phases. The first
phase is the connection phase in which the connection isestablished. cu then enters the conversation phase. The -d
option is the only one that applies to both phases. OPTIONScu accepts many options. The -c, -l, and -s options play a
part in selecting the medium. The remaining options are used in configuring the line.-b bits Forces bits to be the number of bits processed
on the line. bits is either 7 or 8. Thisallows connection between systems with dif-
ferent character sizes. By default, the char-
acter size of the line is set to the same valueas the current local terminal, but the charac-
ter size setting is affected by LC_CTYPE also.
-c device Forces cu to use only entries in the "Type"
field (the first field in the /etc/uucp/Devices file) that match the user specified device, usually the name of a local area network.
-C Runs the local-cmd specified at the end of the
command line instead of entering interactive mode. The stdin and stdout of the command that is run refer to the remote connection.-d Prints diagnostic traces.
-e Sets an EVEN data parity. This option desig-
nates that EVEN parity is to be generated for data sent to the remote system.SunOS 5.11 Last change: 11 May 2001 1
Communication Commands cu(1C)
-h Sets communication mode to half-duplex. This
option emulates local echo in order to support calls to other computer systems that expectterminals to be set to half-duplex mode.
-H Ignores one hangup. This allows the user to
remain in cu while the remote machine discon-
nects and places a call back to the localmachine. This option should be used when con-
necting to systems with callback or dialbackmodems. Once the callback occurs subsequent
hangups will cause cu to terminate. This
option can be specified more than once. For more information about dialback configuration, see remote(4) and System Administration Guide: IP Services-l line Specifies a device name to use as the communi-
cation line. This can be used to override the search that would otherwise take place for the first available line having the right speed.When the -l option is used without the -s
option, the speed of a line is taken from the/etc/uucp/Devices file record in which line matches the second field (the Line field). When
the -l and -s options are both used together,
cu will search the /etc/uucp/Devices file to
check if the requested speed for the requested line is available. If so, the connection will be made at the requested speed, otherwise, an error message will be printed and the call will not be made. In the general case where aspecified device is a directly connected asyn-
chronous line (for instance, /dev/term/a), a telephone number (telno) is not required. Thespecified device need not be in the /dev direc-
tory. If the specified device is associated with an auto dialer, a telephone number must be provided.-L Goes through the login chat sequence specified
in the /etc/uucp/Systems file. For more infor-
mation about the chat sequence, see System Administration Guide: IP Services-n Requests user prompt for telephone number. For
added security, this option will prompt the
user to provide the telephone number to beSunOS 5.11 Last change: 11 May 2001 2
Communication Commands cu(1C)
dialed, rather than taking it from the command line.-o Sets an ODD data parity. This option desig-
nates that ODD parity is to be generated for data sent to the remote system.-s speed Specifies the transmission speed (300, 1200,
2400, 4800, 9600, 19200, 38400). The default value is "Any" speed which will depend on theorder of the lines in the /etc/uucp/Devices file.
-t Dials a terminal which has been set to auto
answer. Appropriate mapping of carriage-return
to carriage-return-line-feed pairs is set.
OPERANDS The following operands are supported: telno When using an automatic dialler, specifies thetelephone number with equal signs for secon-
dary dial tone or minus signs placed appropri-
ately for delays of 4 seconds. systemname Specifies a uucp system name, which can be used rather than a telephone number; in thiscase, cu will obtain an appropriate direct
line or telephone number from a system file.USAGE
Connection Phasecu uses the same mechanism that uucp(1C) does to establish a
connection. This means that it will use the uucp controlfiles /etc/uucp/Devices and /etc/uucp/Systems. This gives cu
the ability to choose from several different media to estab-
lish the connection. The possible media include telephone lines, direct connections, and local area networks (LAN).The /etc/uucp/Devices file contains a list of media that are
available on your system. The /etc/uucp/Systems file con-
tains information for connecting to remote systems, but it is not generally readable.Note: cu determines which /etc/uucp/Systems and
/etc/uucp/Devices files to use based upon the name used to
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Communication Commands cu(1C)
invoke cu. In the simple case, this name will be "cu", but
you could also have created a link to cu with another name,
such as "pppcu", in which case cu would then look for a
"service=pppcu" entry in the /etc/uucp/Sysfiles file to
determine which /etc/uucp/Systems file to use. The telno or systemname parameter from the command line is
used to tell cu what system you wish to connect to. This
parameter can be blank, a telephone number, a system name, or a LAN specific address.telephone number A telephone number is a string consist-
ing of the tone dial characters (thedigits 0 through 9, *, and #) plus the
special characters = and -. The equal
sign designates a secondary dial tone and the minus sign creates a 4 second delay.system name A system name is the name of any com-
puter that uucp can call; the uuname(1C) command prints a list of these names.LAN address The documentation for your LAN will
show the form of the LAN specific address.If cu's default behavior is invoked (not using the -c or -l
options), cu will use the telno or systemname parameter to
determine which medium to use. If a telephone number isspecified, cu will assume that you wish to use a telephone
line and it will select an automatic call unit (ACU). Other-
wise, cu will assume that it is a system name. cu will fol-
low the uucp calling mechanism and use the /etc/uucp/Systems
and /etc/uucp/Devices files to obtain the best available
connection. Since cu will choose a speed that is appropriate
for the medium that it selects, you may not use the -s
option when this parameter is a system name.The -c and -l options modify this default behavior. -c is
most often used to select a LAN by specifying a Type fieldfrom the /etc/uucp/Devices file. You must include either a
telno or systemname value when using the -c option. If the
connection to systemname fails, a connection will be attempted using systemname as a LAN specific address. The-l option is used to specify a device associated with a
SunOS 5.11 Last change: 11 May 2001 4
Communication Commands cu(1C)
direct connection. If the connection is truly a direct con-
nection to the remote machine, then there is no need to specify a systemname. This is the only case where a telno or systemname parameter is unnecessary. On the other hand, there may be cases in which the specified device connects to a dialer, so it is valid to specify a telephone number. The-c and -l options should not be specified on the same com-
mand line. Conversation PhaseAfter making the connection, cu runs as two processes. The
transmit process reads data from the standard input and, except for lines beginning with ~, passes it to the remote system. The receive process accepts data from the remote system and, except for lines beginning with ~, passes it tothe standard output. Normally, an automatic DC3/DC1 protocol is used to control input from the remote so the buffer is not overrun. Lines beginning with ~ have special meanings. Commands The transmit process interprets the following user initiated commands: ~. Terminates the conversation. ~! Escapes to an interactive shell on the local system. ~!cmd... Runs cmd on the local system (via
sh -c).
~$cmd... Runs cmd locally and send its
output to the remote system.~%cd Changes the directory on the
local system. Note: ~!cd will cause the command to be run by asub-shell, probably not what was
intended.~%take from [to] Copies file from (on the remote
system) to file to on the local system. If to is omitted, the from argument is used in both places.SunOS 5.11 Last change: 11 May 2001 5
Communication Commands cu(1C)
~%put from [to] Copies file from (on local sys-
tem) to file to on remote system.If to is omitted, the from argu-
ment is used in both places. ~~line Sends the line ~ line to the remote system.~%break Transmits a BREAK to the remote
system (which can also be speci-
fied as ~%b).
~%debug Toggles the -d debugging option
on or off (which can also bespecified as ~%d).
~t Prints the values of the termio structure variables for the user's terminal (useful for debugging). ~l Prints the values of the termio structure variables for the remote communication line (useful for debugging).~%ifc Toggles between DC3/DC1 input
control protocol and no input control. This is useful when the remote system does not respondproperly to the DC3 and DC1 char-
acters (can also be specified as~%nostop).
~%ofc Toggles the output flow control
setting. When enabled, outgoing data may be flow controlled by the remote host (can also bespecified as ~%noostop).
~%divert Allows/disallows unsolicited
diversions. That is, diversionsnot specified by ~%take.
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Communication Commands cu(1C)
~%old Allows/disallows old style syntax
for received diversions.~%nostop Same as ~%ifc.
The receive process normally copies data from the remote system to the standard output of the local system. It may also direct the output to local files.The use of ~%put requires stty(1) and cat(1) on the remote
side. It also requires that the current erase and kill char-
acters 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 the existence of echo(1) and
cat(1) on the remote system, and that the remote system must be using the Bourne shell, sh. Also, tabs mode (see stty(1)) should be set on the remote system if tabs are to be copied without expansion to spaces.When cu is used on system X to connect to system Y and sub-
sequently used on system Y to connect to system Z, commandson system Y can be executed by using ~~. Executing a tilde
command reminds the user of the local system uname. Forexample, uname can be executed on Z, X, and Y as follows:
uname Z ~[X]!uname X ~~[Y]!uname YIn general, ~ causes the command to be executed on the ori-
ginal machine. ~~ causes the command to be executed on the
next machine in the chain.EXAMPLES
Example 1 Dialling a system To dial a system whose telephone number is 9 1 201 555 1234 using 1200 baud (where dialtone is expected after the 9):SunOS 5.11 Last change: 11 May 2001 7
Communication Commands cu(1C)
example% cu -s 1200 9=12015551234
If the speed is not specified, "Any" is the default value. Example 2 Logging in to a system on a direct line To login to a system connected by a direct line:example% cu -l /dev/term/b
orexample% cu -l term/b
Example 3 Dialling a system with specific line and speed To dial a system with a specific line and speed:example% cu -s 1200 -l term/b
Example 4 Using a system name To use a system name:example% cu systemname
ENVIRONMENT VARIABLES See environ(5) for descriptions of the following environmentvariables that affect the execution of cu: LC_CTYPE,
LC_MESSAGES, and NLSPATH.
SunOS 5.11 Last change: 11 May 2001 8
Communication Commands cu(1C)
EXIT STATUS The following exit values are returned: 0 Successful completion.>0 An error occurred.
FILES/etc/uucp/Devices device file
/etc/uucp/Sysfiles system file
/etc/uucp/Systems system file /var/spool/locks/* lock file
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Availability | service/network/uucp ||_____________________________|_____________________________|
SEE ALSO
cat(1), echo(1), stty(1), tip(1), uname(1), ct(1C), uuname(1C), uucp(1C), remote(4), attributes(5), environ(5) System Administration Guide: IP Services NOTESThe cu utility takes the default action upon receipt of sig-
nals, with the exception of: SIGHUP Close the connection and terminate. SIGINT Forward to the remote system.SunOS 5.11 Last change: 11 May 2001 9
Communication Commands cu(1C)
SIGQUIT Forward to the remote system.SIGUSR1 Terminate the cu process without the normal con-
nection closing sequence.The cu command does not do any integrity checking on data it
transfers. Data fields with special cu characters may not be
transmitted properly. Depending on the interconnection hardware, it may be necessary to use a ~. to terminate theconversion, even if stty 0 has been used. Non-printing char-
acters are not dependably transmitted using either the ~%put
or ~%take commands. ~%put and ~%take cannot be used over
multiple links. Files must be moved one link at a time.There is an artificial slowing of transmission by cu during
the ~%put operation so that loss of data is unlikely. Files
transferred using ~%take or ~%put must contain a trailing
newline, otherwise, the operation will hang. Entering aControl-D command usually clears the hang condition.
SunOS 5.11 Last change: 11 May 2001 10