In contrast to simpler file transfer programs, UUCP was designed to be
able to handle all transfers automatically. Once it is set up
properly, interference by the administrator should not be necessary on
a day-to-day basis. The information required for automated transfer is
kept in a couple of configuration files that reside in the
/usr/lib/uucp directory. Most of these files are
used only when dialing out.
To say that UUCP configuration is difficult would be an understatement. It
is really a hairy subject, and the sometimes terse format of the
configuration files doesn't make things easier (although the Taylor format is
almost easy reading compared to the older formats in HDB or Version 2).
To give you a feel for how all the configuration files interact, we will
introduce you to the most important ones and have a look at sample entries
from these files. We won't explain everything in detail now; a more accurate
account is given in separate sections that follow. If you want to set up your
machine for UUCP, you had best start with some sample files and adapt
them gradually. You can pick either those shown below or those included in
your favorite Linux distribution.
All files described in this section are kept in
/etc/uucp or a subdirectory thereof. Some Linux
distributions contain UUCP binaries that have support for both HDB and Taylor
configuration enabled, and use different subdirectories for each configuration
file set. There will usually be a README file in
/usr/lib/uucp.
For UUCP to work properly, these files must be owned by the
uucp user. Some of them contain
passwords and telephone numbers, and therefore should have permissions
of 600. Note that although most UUCP commands must be setuid to
uucp, you must make sure the
uuchk program is
not. Otherwise, users will be able to display
system passwords even though the files have mode 600.
The central UUCP configuration file is
/etc/uucp/config, which is used to set general
parameters. The most important of them (and for now, the only one) is
your host's UUCP name. At the Virtual Brewery, they use vstout as their UUCP gateway:
# /etc/uucp/config - UUCP main configuration file
nodename vstout |
The sys file is the next important configuration file. It
contains all the system-specific information of sites to which you are linked.
This includes the site's name and information on the link itself, such as the
telephone number when using a modem link. A typical entry for a
modem-connected site called pablo
would look like this:
# /usr/lib/uucp/sys - name UUCP neighbors
# system: pablo
system pablo
time Any
phone 555-22112
port serial1
speed 38400
chat ogin: vstout ssword: lorca |
time specifies the times at
which the remote system may be called. chat describes the login chat
scripts—the sequence of strings that must be exchanged to allow
uucico to log into pablo. We will get back to chat scripts
later. The port keyword simply
names an entry in the port file. (Refer to Figure 16-1.) You can assign whatever name you
like as long as it refers to a valid entry in
port.
The port file holds information specific to the
link itself. For modem links, it describes the device special file to
be used, the range of speeds supported, and the type of dialing
equipment connected to the port. The following entry describes
/dev/ttyS1 (a.k.a. COM 2), to which the
administrator has connected a NakWell modem capable of running at
speeds up to 38,400 bps. The port's name is chosen to match the port
name given in the sys file:
# /etc/uucp/port - UUCP ports
# /dev/ttyS1 (COM2)
port serial1
type modem
device /dev/ttyS1
speed 38400
dialer nakwell |
The information pertaining to the dialers is kept in yet another file
called—you guessed it—dial. For each dialer
type, it basically contains the sequence of commands that are issued to dial up
a remote site, given the telephone number. Again, this is specified as a chat
script. For example, the entry for NakWell might look like this:
# /etc/uucp/dial - per-dialer information
# NakWell modems
dialer nakwell
chat "" AT&F OK ATDT\T CONNECT |
The line starting with chat
specifies the modem chat, which is the sequence of commands sent to
and received from the modem to initialize it and make it dial the
desired number. The \T
sequence will be replaced with the phone number by
uucico.
To give you a rough idea how uucico deals with these
configuration files, assume you issue the following command:
The first thing uucico does is look up pablo in the sys
file. From the sys file entry for pablo, it sees that it should use the
serial1 port to establish the
connection. The port file tells
uucico that this is a modem port, and that it has a
NakWell modem attached.
uucico now searches dial for
the entry describing the NakWell modem, and having found one, opens
the serial port /dev/cua1 and executes the dialer
chat. That is, it sends AT&F, waits for the
OK response, etc. When encountering the string
\T, it substitutes the phone
number (555-22112) extracted from the sys file.
After the modem returns CONNECT, the connection has been
established, and the modem chat is complete. uucico now
returns to the sys file and executes the login chat. In
our example, it would wait for the login: prompt, then send
its username (vstout), wait for the
password: prompt, and send its password
(lorca).
After completing authorization, the remote end is assumed to fire up its own
uucico. The two then enter the handshake phase
described in the previous section.
Figure 16-1 illustrates the dependencies among
configuration files.
Before you start writing the UUCP configuration files, you have to gather some
information that UUCP requires.
First, you have to figure out what serial device your modem is
attached to. Usually, the (DOS) ports COM1: through COM4: map to the
device special files /dev/ttyS0 through
/dev/ttyS3. Some distributions, such as
Slackware, create a link called /dev/modem to the
appropriate ttyS* device file, and configure
kermit, seyon, and any other
communication programs to use this generic file. In this case, you
should use /dev/modem in your UUCP configuration,
too.
The reason for using a symbolic link is that all dial-out programs use
so-called lock files to signal when a serial port is
in use. The names of these lock files are a concatenation of the string
LCK.. and the device filename, for instance
LCK..ttyS1. If programs use different names for the
same device, they will fail to recognize each other's lock files. As a
consequence, they will disrupt each other's session when started at the
same time. This is quite possible when you schedule your UUCP calls
using a crontab entry.
For details on serial port setup, please refer to
Chapter 4.
Next, you must find out at what speed your modem and Linux will communicate.
You have to set this speed to the maximum effective transfer rate you expect
to get. The effective transfer rate may be much higher than the raw physical
transfer rate your modem is capable of. For instance, many modems send and
receive data at 56 kbps. Using compression protocols such as V.42bis, the
actual transfer rate may climb over 100 kbps.
Of course, if UUCP is to do anything at all, you need the phone number
of a system to call. Also, you need a valid login ID and possibly a
password for the remote machine.[1]
You also have to know exactly how to log into the
system. Do you have to press the Enter key before the login prompt appears?
Does it display login: or user:? This
is necessary for composing the chat script. If you don't
know, or if the usual chat script fails, try to call the system with a terminal
program like kermit or minicom and
record exactly what you have to do.
As with TCP/IP-based networking, your host has to have a name for UUCP
networking. As long as you simply want to use UUCP for file transfers to or
from sites you dial up directly, or on a local network, this name does not
have to meet any standards.[2]
However, if you use UUCP for a mail or news link, you should think
about having the name registered with the UUCP Mapping Project.[3] The UUCP Mapping Project is described in
Chapter 17. Even if you participate in a domain,
you might consider having an official UUCP name for your site.
Frequently, people choose their UUCP name to match the first component of
their fully qualified domain name. Suppose your site's domain address is
swim.twobirds.com; then your UUCP
hostname would be swim. Think of UUCP
sites as knowing each other on a first-name basis. Of course, you can also
use a UUCP name completely unrelated to your fully qualified domain name.
However, make sure not to use the unqualified site name in mail addresses
unless you have registered it as your official UUCP
name. At the very best, mail to an unregistered UUCP host will vanish in some big black bit bucket. If you use a name already held by some other site, this
mail will be routed to that site and cause its postmaster a lot of headaches.
By default, the UUCP suite uses the name set by hostname as
the site's UUCP name. This name is commonly set by a command on the boot
time rc scripts, and is usually stored in the
/etc/hostname. If your UUCP name is different from what
you set your hostname to, you have to use the
hostname option in the
config file to tell uucico about your
UUCP name. This is described next.
We now return to the configuration files. Taylor UUCP gets its information
from the following files:
- config
This is the main configuration file. You can define your site's UUCP name here.
- sys
This file describes all known sites. For each site, it specifies its
name, what times to call it, which number to dial (if any), what type of device
to use, and how to log on.
- port
This file contains entries describing each available port, together with the line speed
supported and the dialer to be used.
- dial
This file describes dialers used to establish a telephone connection.
- dialcode
This file contains expansions for symbolic dial codes.
- call
This file contains the login name and password to be used when calling a system.
Rarely used.
- passwd
This file contains login names and passwords that systems may use when logging in. It is used only when uucico does its own password
checking.
Taylor configuration files are generally made up of lines containing
keyword-value pairs. A hash sign introduces a comment that extends to the
end of the line. To use a hash sign to mean itself, escape it with a
backslash like this: \#.
There are quite a number of options you can tune with these configuration
files. We can't go into all the parameters, but we will cover the
most important ones here. Then you should be able to configure a modem-based
UUCP link. Additional sections describe the modifications necessary if you
want to use UUCP over TCP/IP or over a direct serial line. A complete
reference is given in the Texinfo documents that accompany the Taylor UUCP
sources.
When you think you have configured your UUCP system completely, you can check
your configuration using the uuchk tool (located in
/usr/lib/uucp). uuchk reads your
configuration files and prints out a detailed report of the configuration
values used for each system.
You won't generally use this file to describe much beside your UUCP hostname.
By default, UUCP will use the name you set with the hostname
command, but it is generally a good idea to set the UUCP name explicitly. Here's a sample config file:
# /usr/lib/uucp/config - UUCP main configuration file
hostname vstout |
A number of miscellaneous parameters can be set here too, such as the name of
the spool directory or access rights for anonymous UUCP. The latter will be
described later in this chapter in the section “Anonymous UUCP.”
The sys file describes the systems that your
machine knows about. An entry is introduced by the system keyword; the subsequent lines up to
the next system directive
detail the parameters specific to that site. Commonly, a system entry
defines parameters such as the telephone number and login chat.
Parameters before the very first system line set default values used for
all systems. Usually, you set protocol parameters and the like in
the defaults section.
The most prominent fields are discussed in detail in the following sections.
The system command names the remote
system. You must specify the correct name of the remote system, not an alias
you invented, because uucico will check it against what
the remote system says it is called when you log
on.[4]
Each system name can appear only once. If you want to use several sets of
configurations for the same system (such as different telephone numbers
uucico should try in turn), you can specify
alternates, which we'll describe after the basic
configuration options.
If the remote system is to be reached over a telephone line, the
phone field specifies the number the
modem should dial. It may contain several tokens interpreted by
uucico's dialing procedure. An equal sign (=) means wait
for a secondary dial tone, and a dash (-) generates a one-second pause. Some
telephone installations choke when you don't pause between
dialing a special access code and the telephone
number.[5]
It is often convenient to use names instead of numbers to describe
area dialing codes. The dialcode file allows you to
associate a name with a code that you may subsequently use when specifying
telephone numbers for remote hosts. Suppose you have the following
dialcode file:
# /usr/lib/uucp/dialcode - dialcode translation
Bogoham 024881
Coxton 035119 |
With these translations, you can use a phone number such as
Bogoham7732 in the
sys file, which will probably make things a little more
legible and a whole lot easier to update should the dialing code for
Bogoham ever change.
The port and speed options are used to select the
device used for calling the remote system and the maximum speed to
which the device should be set.[6]
A system entry may
use either option alone or both options in conjunction. When looking
up a suitable device in the port file, only ports that have a matching port name and/or speed range are selected.
Generally, using the speed
option only should suffice. If you have only one serial device defined
in port, uucico always picks the right one anyway, so you only have to give it the desired
speed. If you have several modems attached to your systems, you still
often don't want to name a particular port, because if
uucico finds that there are several matches, it
tries each device in turn until it finds an unused one.
We already encountered the login chat script, which tells
uucico how to log in to the remote system. It
consists of a list of tokens specifying strings expected and sent by
the local uucico process. uucico
waits until the remote machine sends a login prompt, then returns the
login name, waits for the remote system to send the password prompt,
and sends the password. Expect and send strings appear in alternation
in the script. uucico automatically appends a
carriage return character (\r)
to any send string. Thus, a simple chat script would look like:
ogin: vstout ssword: catch22 |
You will probably notice that the expect fields don't contain the
whole prompts. This ensures that the login succeeds, even if the
remote system transmits Login: instead of
login:. If the string you are expecting or sending
contains spaces or other white-space characters, you must use quotes
to surround the text.
uucico also allows for some sort of conditional execution.
Let's say the remote machine's getty
needs to be reset before sending a prompt. For this, you can attach a subchat
to an expect string, set off by a dash. The subchat is executed only if the
main expect fails, i.e., a timeout occurs. One way to use this feature is to
send a BREAK if the remote site doesn't display a login prompt. The following
example gives a general-purpose chat script that should also work in case you
have to press Enter before the login appears. The empty first argument,
"", tells UUCP to not wait for anything, but to continue
with the next send string:
"" \n\r\d\r\n\c ogin:-BREAK-ogin: vstout ssword: catch22 |
A couple of special strings and escape characters can occur in the chat
script. The following is a partial list of characters legal in expect strings:
- ""
The empty string. It tells uucico to not wait for anything,
but to proceed with the next send string immediately.
- \t
Tab character.
- \r
Carriage return character.
- \s
Space character. You need this to embed spaces in a chat string.
- \n
Newline character.
- \\
Backslash character.
On send strings, the following escape characters and strings are legal in
addition to the above:
- EOT
End of transmission character (^D).
- BREAK
Break character.
- \c
Suppress sending of carriage return at end of string.
- \d
Delay sending for 1 second.
- \E
Enable echo checking. This requires uucico to wait for the
echo of everything it writes to be read back from the device before it can
continue with the chat. It is primarily useful when used in modem chats
(which we will encounter later). Echo checking is off by default.
- \e
Disable echo checking.
- \K
Same as BREAK.
- \p
Pause for fraction of a second.
Sometimes you want to have multiple entries for a single system, for
instance if the system can be reached on different modem lines. With Taylor
UUCP, you can do this by defining a so-called alternate.
An alternate entry retains all settings from the main system entry and
specifies only those values that should be overridden in the default system
entry or added to it. An alternate is offset from the system entry by a
line containing the keyword alternate.
To use two phone numbers for pablo,
you would modify its sys entry in the following way:
system pablo
phone 123-456
.. entries as above ...
alternate
phone 123-455 |
When calling pablo,
uucico will first dial 123-456, and if this fails, it will
try the alternate. The alternate entry retains all settings from the main
system entry and overrides the telephone number only.
Taylor UUCP provides a number of ways you may restrict the times when calls
can be placed to a remote system. You might do this either because of
limitations the remote host places on its services during business hours, or
simply to avoid times with high call rates. Note that it is always possible
to override call-time restrictions by giving uucico the
–S or –f option.
By default, Taylor UUCP disallows connections at any time, so you
have to use some sort of time specification in the
sys file. If you don't care about call time restrictions,
you can specify the time option with a
value of Any in your
sys file.
The simplest way to restrict call time is to include a
time entry, followed by a string made
up of a day and a time subfield. Day may be any combination of
Mo, Tu, We, Th, Fr, Sa, and Su. You can
also specify Any,
Never, or
Wk for weekdays. The time consists of
two 24-hour clock values, separated by a dash. They specify the range during
which calls may be placed. The combination of these tokens is written without
white space in between. Any number of day and time specifications may be
grouped together with commas, as this line shows:
time MoWe0300-0730,Fr1805-2200 |
This example allows calls on Mondays and Wednesdays from 3:00 a.m. to 7:30 a.m.,
and on Fridays between 6:05 p.m. and 10:00 p.m. When a time field spans
midnight, say Mo1830-0600, it actually
means Monday, between midnight and 6:00 a.m. and between 6:30 p.m. and midnight.
The special time strings Any and
Never mean what they say: calls may be
placed at any or no time, respectively.
Taylor UUCP also has a number of special tokens you may use in time strings,
such as NonPeak and
Night. These special tokens are shorthand for
Any2300-0800,SaSu0800-1700 and
Any1800-0700,SaSu, respectively.
The time command takes an optional
second argument that describes a retry time in minutes. When an attempt to
establish a connection fails, uucico will not allow another
attempt to dial up the remote host within a certain interval. For instance,
when you specify a retry time of 5 minutes, uucico will
refuse to call the remote system within 5 minutes after the last failure. By
default, uucico uses an exponential backoff scheme, where
the retry interval increases with each repeated failure.
The timegrade command allows you to
attach a maximum spool grade to a schedule. For instance, assume you have the
following timegrade commands in a
system entry:
timegrade N Wk1900-0700,SaSu
timegrade C Any |
This allows jobs with a spool grade of C or higher (usually mail is queued
with grade B or C) to be transferred whenever a call is established, while
news (usually queued with grade N) are transferred only during the night
and at weekends.
Just like time, the timegrade command takes a retry interval in minutes as an optional third argument.
However, a caveat about spool grades is in order here. First, the
timegrade option applies only to what
your systems sends; the remote system may still transfer
anything it likes. You can use the
call-timegrade option to explicitly
request it to send only jobs above some given spool grade; but there's no
guarantee it will obey this request.[7]
Similarly, the timegrade field is not
checked when a remote system calls in, so any jobs queued for the calling
system will be sent. However, the remote system can explicitly request your
uucico to restrict itself to a certain spool grade.
The port file tells uucico about the
available ports. These are usually modem ports, but other types, such as direct
serial lines and TCP sockets, are supported as well.
Like the sys file, port
consists of separate entries starting with the keyword
port followed by the port name. This
name may be used in the sys file's
port statement. The name need not
be unique; if there are several ports with the same name,
uucico will try each in turn until it finds one that
is not currently being used.
The port command should be followed
immediately by the type statement,
which indicates what type of port is described. Valid types are
modem,
direct for direct connections, and
tcp for TCP sockets. If the
port command is missing, the port
type defaults to modem.
In this section, we cover only modem ports; TCP ports and direct lines are
discussed in a later section.
For modem and direct ports, you have to specify the device for calling out
using the device directive. Usually,
this is the name of a device special file in the /dev
directory, like /dev/ttyS1.
In the case of a modem device, the port entry also determines what type of
modem is connected to the port. Different types of modems have to be
configured differently. Even modems that claim to be Hayes-compatible aren't
always really compatible with one another. Therefore, you have to tell
uucico how to initialize the modem and make it dial
the desired number. Taylor UUCP keeps the descriptions of all dialers in a
file named dial. To use any of these, you have to specify
the dialer's name using the dialer
command.
Sometimes, you will want to use a modem in different ways, depending on which
system you call. For instance, some older modems don't understand when a
high-speed modem attempts to connect at 56 kbps; they simply drop the line
instead of negotiating a connect at 9,600 bps, for instance. When you know site
drop uses such a dumb modem, you have
to set up your modem differently when calling them. For this, you need an
additional port entry in the port file that specifies a
different dialer. Now you can give the new port a different name, such as
serial1-slow, and use the
port directive in the
drop system entry in
sys.
A better to distinguish the ports is by the speeds they support. For
instance, the two port entries for the above situation may look like this:
# NakWell modem; connect at high speed
port serial1 # port name
type modem # modem port
device /dev/ttyS1 # this is COM2
speed 115200 # supported speed
dialer nakwell # normal dialer
# NakWell modem; connect at low speed
port serial1 # port name
type modem # modem port
device /dev/ttyS1 # this is COM2
speed 9600 # supported speed
dialer nakwell-slow # don't attempt fast connect |
The system entry for site drop would
now give serial1 as the port name, but
request to use it at only 9,600 bps. uucico then
automatically uses the second port entry. All remaining sites that have a
speed of 115,200 bps in the system entry will be called using the first port
entry. By default, the first entry with a matching speed will be used.
The dial file describes the way various dialers are used.
Traditionally, UUCP talks of dialers rather than modems, because in earlier
times, it was usual practice to have one (expensive) automatic dialing device
serve a whole bank of modems. Today, most modems have dialing support built
in, so this distinction gets a little blurred.
Nevertheless, different dialers or modems may require a different
configuration. You can describe each of them in the
dial file. Entries in dial
start with the dialer command
that gives the dialer's name.
The most important entry besides dialer is the modem chat, specified by the chat command. Similar to the
login chat, it consists of a sequence of strings
uucico sends to the dialer and the responses it
expects in return. It is commonly used to reset the modem to some
known state and dial the number. The following sample dialer entry shows a typical modem chat
for a Hayes-compatible modem:
# NakWell modem; connect at high speed
dialer nakwell # dialer name
chat "" AT&F OK\r ATH1E0Q0 OK\r ATDT\T CONNECT
chat-fail BUSY
chat-fail ERROR
chat-fail NO\sCARRIER
dtr-toggle true |
The modem chat begins with "", the empty expect
string. uucico therefore sends the first
command AT&F right
away. AT&F is the Hayes command to reset the
modem to factory default configuration. uucico
then waits until the modem has sent OK and sends
the next command, which turns off local echo and the like. After the
modem returns OK again, uucico
sends the dialing command ATDT. The escape
sequence \T in this string is replaced with the
phone number taken from the system entry sys
file. uucico then waits for the modem to return the
string CONNECT, which signals that a connection
with the remote modem has been established successfully.
Sometimes the modem fails to connect to the remote system; for instance,
if the other system is talking to someone else and the line is busy. In this
case, the modem returns an error message indicating the reason. Modem
chats are not capable of detecting such messages; uucico
continues to wait for the expected string until it times out. The UUCP
log file therefore only shows a bland “timed out in chat
script” instead of the specific reason.
However, Taylor UUCP allows you to tell uucico about these
error messages using the chat-fail
command as shown above. When uucico detects a chat-fail
string while executing the modem chat, it aborts the call and logs the error
message in the UUCP log file.
The last command in the example shown above tells UUCP to toggle the Data Terminal Ready (DTR) control line before starting the modem chat. Normally,
the serial driver raises DTR when a process opens the device to tell the
attached modem that someone wants to talk to it. The
dtr-toggle feature then drops DTR,
waits a moment, and raises it again. Many modems can be configured
to react to a drop of DTR by going off-hook, entering command state, or
resetting themselves.[8]
Absurd as it may sound, using UUCP to transfer data over TCP is not that bad
an idea, especially when transferring large amounts of data such as Usenet
news. On TCP-based links, news is generally exchanged using the NNTP
protocol, through which articles are requested and sent individually without
compression or any other optimization. Although adequate for large sites
with several concurrent newsfeeds, this technique is very unfavorable for
small sites that receive their news over a relatively slow connection such
as ISDN. These sites will usually want to combine the qualities of TCP with
the advantages of sending news in large batches, which can be compressed and
thus transferred with very low overhead. A common way to transfer these
batches is to use UUCP over TCP.
In sys, you would specify a system to be called via TCP
like this:
system gmu
address news.groucho.edu
time Any
port tcp-conn
chat ogin: vstout word: clouseau |
The address command gives the
IP address of the host or its fully qualified domain name. The
corresponding port entry would read:
port tcp-conn
type tcp
service 540 |
The entry states that a TCP connection should be used when a
sys entry references
tcp-conn, and that
uucico should attempt to connect to the TCP network port
540 on the remote host. This is the default port number of the UUCP service.
Instead of the port number, you may also give a symbolic port name to the
service command. The port number
corresponding to this name will be looked up in
/etc/services. The common name for the UUCP service is
uucpd.
Assume you use a direct line to connect your system
vstout to
tiny. Much like in the modem case,
you have to write a system entry in the sys file. The
port command identifies the serial port
tiny is hooked up to:
system tiny
time Any
port direct1
speed 38400
chat ogin: cathcart word: catch22 |
In the port file, you have to describe the serial port
for the direct connection. A dialer
entry is not needed because there's no need for dialing:
port direct1
type direct
speed 38400
device /dev/ttyS1 |
