cu(1C) (Basic Networking Utilities) cu(1C)
NAME
cu - call another UNIX system
SYNOPSIS
cu [ options ] [ destination ]
DESCRIPTION
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 convenient to think of cu as operating in
two phases. The first phase is the connection phase in which the
connection is established. cu then enters the conversation phase.
The -d option is the only one that applies to both phases.
-d Causes diagnostic traces to be printed.
Connection Phase
cu uses the same mechanism that uucp does to establish a connection.
This means that it will use the uucp control files /etc/uucp/Devices
and /etc/uucp/Systems. This gives cu the ability to choose from
several different media to establish the connection. The possible
media include telephone lines, direct connections, and local area
networks (LAN). The Devices file contains a list of media that are
available on your system. The Systems file contains information for
connecting to remote systems, but it is not generally readable.
The destination parameter from the command line is used to tell cu
what system you wish to connect to. destination can be blank, a
telephone number, a system name, or a LAN specific address. A
telephone number is a string consisting of the tone dial characters
(the digits 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. A system name is the name of any
computer that uucp can call; the uuname command prints a list of
these names. 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 destination to determine which medium to use. If
destination is a telephone number, cu will assume that you wish to
use a telephone line and it will select an automatic call unit (ACU).
If the destination is not a telephone number, then cu will assume
that it is a system name. cu will follow the uucp calling mechanism
and use the Systems and 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
destination 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 field from the Devices
file. Here, destination is assumed to be a system name. If the
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connection attempt to system name fails, a connection will be
attempted using destination as a LAN specific address. The -l option
is used to specify a device associated with a direct connection. If
the connection is truly a direct connection to the remote machine,
then there is no need to specify a destination. This is the only
case where a blank destination is allowed. 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 as a destination. The -c
and -l options should not be specified on the same command line.
cu 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.
-sspeed Specifies the transmission speed (300, 1200, 2400, 4800,
9600). The default value is "Any" speed which will
depend on the order of the lines in the /etc/uucp/Devices
file. Most modems are either 300, 1200, or 2400 baud.
Directly connected lines may be set to a speed higher
than 2400 baud.
-ctype The first field in the Devices file is the "Type" field.
The -c option forces cu to only use entries in the "Type"
field that match the user specified type. The specified
type is usually the name of a local area network.
-lline Specifies a device name to use as the communication 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 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 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 a specified
device is a directly connected asynchronous line (e.g.,
/dev/term/ab), a telephone number (telno) is not
required. The specified device need not be in the /dev
directory. If the specified device is associated with an
auto dialer, a telephone number must be provided. If
destination is used with this option, it must be a
telephone number.
-bn Forces n to be the number of bits processed on the line.
n is either 7 or 8. This allows connection between
systems with different character sizes. By default, the
character size of the line is set to the same as the
current local terminal.
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-e Set an EVEN data parity. This option designates that
EVEN parity is to be generated for data sent to the
remote system.
-h Set communication mode to half-duplex. This option
emulates the local echo(1) command in order to support
calls to other computer systems that expect terminals to
be set to half-duplex mode.
-n Request user prompt for telephone number. For added
security, this option will prompt the user to provide the
telephone number to be dialed, rather than taking it from
the command line.
-o Set an ODD data parity. This option designates that ODD
parity is to be generated for data sent to the remote
system.
-t Used to dial a terminal which has been set to auto
answer. Appropriate mapping of carriage-return to
carriage-return-line-feed pairs is set.
Conversation Phase
After 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 to the 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.
The transmit process interprets the following user initiated
commands:
~. terminate the conversation.
~! escape to an interactive shell on the local
system.
~!cmd... run cmd on the local system (via sh -c).
~$cmd... run cmd locally and send its output to the remote
system.
~%cd change the directory on the local system. Note:
~!cd will cause the command to be run by a sub-
shell, probably not what was intended.
~%take from [ to ] copy 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.
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~%put from [ to ] copy file from (on local system) to file to on
remote system. If to is omitted, the from
argument is used in both places.
~~ line send the line ~ line to the remote system.
~%break transmit a BREAK to the remote system (which can
also be specified as ~%b).
~%debug toggles the -d debugging option on or off (which
can also be specified 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 respond properly to the
DC3 and DC1 characters. (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 be specified as
~%noostop).
~%divert allow/disallow unsolicited diversions. That is,
diversions not specified by ~%take.
~%old allow/disallow old style syntax for received
diversions.
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 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 the existence of echo(1) and cat(1) on the
remote system. Also, tabs mode (See stty(1)) should be set on the
remote system if tabs are to be copied without expansion to spaces.
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When cu is used on system X to connect to system Y and subsequently
used on system Y to connect to system Z, commands on system Y can be
executed by using ~~. Executing a tilde command reminds the user of
the local system uname. For example, uname can be executed on Z, X,
and Y as follows:
uname
Z
~[X]!uname
X
~~[Y]!uname
Y
In general, ~ causes the command to be executed on the original
machine. ~~ causes the command to be executed on the next machine in
the chain.
EXAMPLES
To dial a system whose telephone number is 9 1 201 555 1234 using
1200 baud (where dialtone is expected after the 9):
cu -s1200 9=12015551234
If the speed is not specified, "Any" is the default value.
To login to a system that is on a Datakit VCS local area network, but
which has not been defined by your administrator (i.e. is not entered
in the /etc/uucp/Systems file(s)):
cu -c DK address
DK is the name of the Datakit local area network, and address is the
Datakit address which is of the form, /area/exchange/machine.
To login to a system connected by a direct line:
cu -l /dev/term/XX
or
cu -l term/XX
To dial a system with a specific line and speed:
cu -s1200 -l term/XX
To dial a system using a specific line associated with an auto
dialer:
cu -l culXX 9=12015551234
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To use a system name:
cu systemname
FILES
/etc/uucp/Sysfiles
/etc/uucp/Systems
/etc/uucp/Devices
/var/spool/locks/*
SEE ALSO
cat(1), ct(1C), echo(1), stty(1), uucp(1C), uname(1), uuname(1).
System Administrator's Guide.
DIAGNOSTICS
Exit code is zero for normal exit, otherwise, one.
WARNINGS
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 the conversion, even if
stty 0 has been used. Non-printing characters are not dependably
transmitted using either the ~%put or ~%take commands. cu, between
an IMBR1 and a PENRIL modem, will not return a login prompt
immediately upon connection. A carriage return will return the
prompt.
~%put and ~%take cannot be used over multiple links. Files must be
moved one link at a time.
BUGS
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 a CTRL-d command usually clears the
hang condition.
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