Systems(4bnu)

Description

The Systems file entries determine your computer's ability to communicate with remote systems both in its role as a client and server machine. Any remote system not defined in the Systems file will not be able to log in to your machine to establish a communication link. Likewise, if a remote system is not defined in the Systems file, your machine will not be able to log in to the remote machine to establish a communication link.

More than one entry can be defined in the Systems file for an individual remote computer. The additional entries represent alternative communication paths to the remote system that will be tried in sequential order.

Blank lines, and lines that begin with white space, a tab, or a hash sign (#) are ignored.

Each entry in the Systems file contains the following fields in the order shown:

``System-Name''

Contains the node name of the remote computer.

``Time''

Specifies when the remote system can be accessed. ``Time'' contains a string that specifies both the day of the week and the time of day when the remote system can be called. The format of the ``Time'' field is:

daytime[;retry]

The day portion of the daytime string is a list containing some of the following:

Su Mo Tu We Th Fr Sa

for individual days

Wk

for any weekday (Mo, Tu, We, Th or Fr)

Any

for any day

Never

for a passive arrangement with the remote computer. This means that your local computer will never initiate a call to the remote computer: the call must be initiated by the remote computer. In other words, your local computer is passive with respect to the remote computer. See Permissions(4bnu).

Any and Never are the most common values used in the ``Time'' field.

The time portion of the daytime string is a range of times specified in 24-hour notation. For example, ``0830-1230'' represents the times of day from 8:30 A.M. to 12:30 P.M. If the time is not specified, any time of day is assumed to be a valid time to call. Note that a time range that spans 0000 hours is permitted. For example, ``0800-0600'' means all times are allowed other than times between 6 A.M. and 8 A.M.

The following is a sample ``Time'' entry:

   Wk1700-0800,Sa,Su

This example allows calls from 5:00 P.M. to 8:00 A.M. Monday through Friday, and calls any time Saturday and Sunday. The example illustrates a typical way you can permit calls to be made only when telephone rates are low.

The optional value, retry, specifies the minimum amount of time (in minutes) that uusched(1Mbnu) should wait before retrying a transmission attempt that fails. The default wait is five minutes. A semicolon (;) is used to separate this value.

For example, Any;9 specifies a call that can be made at any time. If this call fails then it may be retried by uusched (via /var/spool/cron/crontabs/uucp) after waiting for at least nine minutes.

``Type''

Specifies the type of device to be used to establish a communication link with the remote computer. The value of this field is used to access the entry defined for the device type in the Devices(4bnu) file. The ``Type'' entry is matched against the first field of the Devices file entries.

The protocol to be used to contact the remote system can be specified by adding a protocol identifier to the ``Type'' field value. For example, if the ``Type'' field specifies CS and the protocol identifier in the Devices file specifies that the e or g protocol should be used for CS, then the ``Type'' field entry would be:

   CS,eg

Using the protocol information from the Devices file as part of the ``Type'' entry in the Systems file is optional, but it is often done to make entries in both files easier to understand. The device type and the protocols must be comma-separated. In the following Systems file example, the g protocol is attached to the device type ACU:

   #Systems file
   #
   eagle Any ACU,g 38400 3251 ogin: nuucp ssword: password
   

   #Devices file
   #
   ACU term/01m,M - 38400 28-8_Data_Fax_Modem

``Class''

Specifies the transfer speed of the device to be used in establishing the communication link. This field may contain a letter and speed (for example, ``C1200'', ``D1200'') to differentiate between classes of dialers. Some devices can be used at any speed. In this case the keyword Any may be used.

The ``Class'' field of the Systems file must match the ``Class'' field in the associated Devices(4bnu) file entry. If information is not required for the ``Class'' field, a dash (-) must be placed in the field as a placeholder.

``Phone''

Specifies a colon-separated list of telephone numbers or network addresses of the remote computer. If a number in the list fails (for example, hardware failure, line busy) then the Connection Server tries the next number in the list.

---

NOTE: Each connection request starts from the ``current'' position in the list of numbers, rather than from the beginning each time. Preference ordering (for example, local numbers before long-distance numbers) is not assummed.

---

Each telephone number is made up of an optional alphabetic abbreviation and a numeric part. If an abbreviation is used, it must be one that is listed in the Dialcodes(4bnu) file. For example:

   #Systems file
   #
   eagle Any ACU D1200 NY3251 ogin: nuucp ssword: password
   

   #Dialcodes file
   #
   NY 9=1-212635

In this string, the equal sign (=) tells the ACU to wait for a secondary dial tone before dialing the remaining digits. The dash (-) in the string instructs the ACU to pause four seconds before dialing the next digit.

If your computer is connected to a LAN switch, you may access other computers that are connected to that switch. The Systems file entries for these computers will not have a telephone number in the ``Phone'' field. Instead, the ``Phone'' field will contain the token that must be passed to the switch so that it will know which computer your computer wishes to communicate with (this is usually just the system name). The associated Devices file entry should have a \D at the end of the entry to ensure that this field is not translated using the Dialcodes file.

If the ``Type'' entry is CS, any information in the ``Phone'' field is passed to the dials(3N) routine. In this case, the ``Phone'' field may consist of:

system,service

where either or both subfields may contain a dash, or the ``Phone'' field may contain a single dash.

If neither system nor service is specified, the system name (the first field in the entry) and the service name (uucico or cu) will be passed as parameters to dials.

``Login''

Contains the chat script to be used to log in to the remote system, given as a series of fields and subfields of the format:

expect send

where expect is the string that is received and send is the string that is sent in response to receiving the expect string.

The expect string is of the form:

expect[-send-expect]...

where send is sent if the prior expect is not successfully read and the expect following the send is the next expected string. For example, with ogin:--ogin:, uucp will expect ``login''. If uucp gets ``ogin:'', it will go on to the next field. If it does not get ``ogin:'', it will send nothing followed by a newline, then look for ``ogin'' again. If no characters are initially expected from the remote computer, then the null string should be used in the first expect field. Note that all send fields will be sent followed by a newline, unless the send string is terminated with a ``\c''.

Note that the ``l'' and other initial characters are often omitted from chat scripts since chat scripts are case-sensitive: some systems capitalize the first letter of prompts while others do not.

This is an example of a Systems file entry that uses an expect-send string:

   owl Any ACU 1200 Chicago6013 "" \r ogin:-BREAK-ogin: \
   uucpx word: xyzzy

This example says: don't wait, just send a carriage-return and wait for ``ogin:'' (that is, for ``Login:''). If you don't get ``ogin'', send a BREAK. When you do get ``ogin:'', send the login name ``uucpx'', then when you get ``word:'' (for ``Password:''), send the password ``xyzzy''.

There are several escape characters that cause specific actions when they are a part of a string sent during the login sequence. The following escape characters are useful when using BNU communications:

\b

Send or expect a backspace character

\c

If at the end of a string, suppress the newline that is normally sent. Ignored otherwise.

\d

Delay two seconds before sending or reading more characters

\p

Pause for approximately ¼ to ½ second

\E

Start echo checking. (From this point on, whenever a character is transmitted, it will wait for the character to be received before doing anything else.)

\e

Echo check off

\M

Turn on CLOCAL flag

\m

Turn off CLOCAL flag

\n

Send a newline character

\r

Send or expect a carriage-return

\s

Send or expect a space character

\t

Send or expect a tab character

\\

Send or expect a \ character

BREAK

Send or expect a BREAK character

\D

Telephone number or token without Dialcodes translation

EOT

Send or expect EOT newline twice

\K

Same as BREAK

\N

Send or expect a null character (ASCII NUL)

\T

Telephone number or token with Dialcodes translation

\ddd

Collapse the octal digits ddd into a single character

~nn

Specify the timeout by appending nn to the expect string, where nn is the timeout period in seconds.

The ``Login'' field may contain the keyword INVOKE followed by white space followed by the name of an authentication scheme. This pair may appear several times in the ``Login'' field of a Systems file entry if more than one authentication step is expected to take place. The following is an example of a Systems file entry that specifies more than one authentication step:

   sysX Any ACU 1200 95551234 INVOKE "inap -r" \
   INVOKE "cr1 -r"

where sysX is a valid system name.

If the expect string consists of the keyword ABORT, then the string after it is used to arm an ABORT trap. If that string is subsequently received any time prior to the completion of the entire expect-send script, then uucico aborts, as it would if the script had timed out. This is useful for trapping error messages -- such as Host Unavailable or System is Down -- from port selectors or front-end processors. Note that in an expect-send script, the format in which the ABORT appears is backward:

ABORT expect

instead of

expect ABORT

Note also, that the entire ``Login'' field is ignored for cu and ct service requests, since the user is expected to enter the proper connect sequence manually. This means that login chat scripts that include an INVOKE statement will also be ignored when the service being requested is cu or ct.

Files

/etc/uucp/Devices

/etc/uucp/Dialcodes

/etc/uucp/Dialers

Usage

/usr/lib/uucp/remote.unknown is a binary program that executes when a machine not found in any of the entries in your computer's Systems file starts a conversation with your machine. It will log the conversation attempt and drop the connection. Its function is similar to that of a daemon. Note that if you change the permissions of the remote.unknown file so it cannot execute, your system will accept connections from any system.

If a remote system supports machine authentication and is not connected via a Connection Server connection, the entry in the Systems file for this machine must include the appropriate INVOKE-scheme pair or pairs to enforce the use of an authentication scheme. If the cr1(1Mbnu) authentication scheme is not included in the Systems file, passwords will be passed between machines in clear text.

To enforce the use of an authentication scheme, the entry in the Systems file should be:

   INVOKE "cr1 -r"

Systems files from previous releases may be installed without change. This provides backward compatibility without the administrative overhead involved in setting up the Connection Server and cr1.

The Systems.tcp file and pre-UNIX SVR4.0 systems

If you are going to be communicating with a pre-UNIX SVR4.0 system, you must change that system's address in /etc/uucp/Systems.tcp so that the 0401 port number is used. For example, if you had the following entry for machine downtown in your /etc/uucp/Systems.tcp file:

   downtown Any TcpCico10103 - \x00020aceAE026e50

   downtown Any TcpCico10103 - \x00020401AE026e50

References