cu(1C) UNIX System V(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 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
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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.
-e Set an EVEN data parity. This option designates that EVEN
parity is to be generated for data sent to the remote system.
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-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.
~%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.
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~%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 control characters on the remote system be
identical to the current control characters on the local system.
Backslashes are inserted at appropriate places for these control
characters.
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.
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
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cu(1C) UNIX System V(Basic Networking Utilities) cu(1C)
~~[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
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.
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DIAGNOSTICS
Exit code is zero for normal exit, otherwise, one.
NOTES
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.
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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