CU(1) RISC/os Reference Manual CU(1)
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 tele-
phone 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 infor-
mation for connecting to remote systems, but it is not gen-
erally 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 avail-
able 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.
Printed 11/19/92 Page 1
CU(1) RISC/os Reference Manual CU(1)
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 sys-
tem 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 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 communica-
tion 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 tele-
phone number (telno) is not required. The
specified device need not be in the /dev direc-
tory. If the specified device is associated
Page 2 Printed 11/19/92
CU(1) RISC/os Reference Manual CU(1)
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 con-
nection 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.
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 proto-
col is used to control input from the remote so the buffer
is not overrun. Lines beginning with ~ have special mean-
ings.
The transmit process interprets the following user initiated
commands:
~. terminate the conversation.
~! escape to an interactive shell on the
Printed 11/19/92 Page 3
CU(1) RISC/os Reference Manual CU(1)
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 sys-
tem. 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 sys-
tem.
~%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 struc-
ture variables for the user's terminal
(useful for debugging).
~l prints the values of the termio struc-
ture variables for the remote communica-
tion 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.
Page 4 Printed 11/19/92
CU(1) RISC/os Reference Manual CU(1)
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.
When cu is used on system X to connect to system Y and sub-
sequently 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 ori-
ginal machine. ~~ causes the command to be executed on the
next machine in the chain.
INTERNATIONAL FUNCTIONALITY
cu sets the input and output conversion mode to on or off,
as appropriate, to avoid a character conversion on LOCAL
system when accessing the REMOTE system.
On the REMOTE system, the input and output conversion should
be set manually, as cu cannot know whether input conversion
is required or not. In most cases, REMOTE systems can be
used with input conversion on, however when transferring
files, this should be set to off before invoking the file
transfer command in order to avoid unexpected conversion of
the file contents.
Printed 11/19/92 Page 5
CU(1) RISC/os Reference Manual CU(1)
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 administra-
tor (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
To set the conversion mode on or off:
$cu
. . .
# commands to set a character conversion mode to
off
# start of file transfer
$~%put from [to]
$~%take from [to]
# end of file transfer
# commands to set a character conversion mode back
to on
Page 6 Printed 11/19/92
CU(1) RISC/os Reference Manual CU(1)
FILES
/etc/uucp/Sysfiles
/etc/uucp/Systems
/etc/uucp/Devices
/var/spool/locks/*
SEE ALSO
cat(1), ct(1), echo(1), stty(1), uucp(1), uname(1),
uuname(1).
System Administrator's Guide.
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 stty0 has been used. Non-printing char-
acters 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 con-
nection. 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.
Printed 11/19/92 Page 7