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Using Leafnode
INN is a tool that's used mainly by large
ISPs or other organizations that want to provide full news feeds, or by
organizations that want to provide limited local newsgroups in support of their
own activities, but not full news feeds. As described earlier, though, in the
section "
facilitate their own local news reading. Such a server should retrieve messages
from just a few newsgroups, make them available whether or not the main
Internet connection is active, and upload the user's postings during the next
round of message downloads. These scheduled message exchanges could take place
just once or twice a day, at times when the news server is not heavily loaded
or when a Point-to-Point Protocol (PPP) dialup connection is inexpensive or
easy to obtain. In principle, INN could serve this function, but considered as
a server for just a few local users reading a handful of newsgroups, INN is
overkill. The program is also designed to work as a peer on the Usenet network,
so chances are you'd have trouble finding an ISP that would agree to feed a
limited number of newsgroups to you on your own schedule. For these reasons,
other tools exist to help users perform offline news reading. One of the more
popular of these is Leafnode ( target="_blank">http://www.leafnode.org ).NOTE
align=left border=0> Leafnode isn't alone in the class of NNTP
servers for small or offline sites. Others that fill similar roles include
NNTPCache ( http://www.nntpcache.org ), Noffle ( target="_blank">http://noffle.sourceforge.net ), sn ( http://infa.abo.fi/~patrik/sn/ ) and NewsCache (
Understanding
Leafnode's Capabilities
Like INN, Leafnode is actually composed of
several programs. The most important of these are: leafnode This is the NNTP server program. It's launched from a super
server, as described in
communicates with your news reader program on the same or a different computer. fetchnews This program, as its name implies, is responsible for retrieving
news from your upstream news server. It also delivers your posts to the
upstream news server. You can run it as a cron job to retrieve news on a
regular basis, run it in a PPP dialup script, or run it manually. texpire Just like a normal news server, Leafnode retains news messages in
subdirectories of /var/spool/news . Because of this, it's necessary for Leafnode to delete old
messages, lest your hard disk fill up. Doing this is texpire 's job.
It's normally run as a cron job on a daily basis. newsq This is a local information display program; it reports a summary
of news articles that have been posted locally but not yet uploaded to your
upstream news server.Leafnode is designed for dynamic newsgroup
configuration. If a user tries to start reading a newsgroup, Leafnode will
begin fetching that newsgroup with the next run of fetchnews . If Leafnode
detects no attempt to access a newsgroup for some period (a week, by default),
then it stops retrieving the group. This means that you can provide the
illusion that you're carrying all the newsgroups available on your upstream
news provider without actually doing so. Your local users will, however,
experience a delay of one fetch cycle between attempting to access a new group
and seeing the posts that are available in it.One of the more unusual characteristics of
Leafnode is that it doesn't require a full news feed arrangement with the
upstream provider; Leaf node (or fetchnews , to be precise) presents itself
as an ordinary news reader to the feed site. This means that you can use
Leafnode in conjunction with your ISP's ordinary news server.NOTE
align=left border=0> Leafnode uses both greater and fewer
resources than an ordinary news reader. Fetching all the posts in a typical
text newsgroup will probably consume far less time than would a news-reading
session in which you're constantly connected to the remote server. This can
reduce consumption of connections on the server (which are sometimes
limited), as well as your online connect time. On the other hand, this
process consumes far more bandwidth, in terms of bytes transferred, than
would a typical online reading session, since Leafnode downloads all the articleseven those you ordinarily wouldn't
read. If Leafnode serves several users who normally read much the same set of
newsgroups, though, the total amount of data transferred might not be more
with Leafnode than with individual direct connections.
In early 2002, the current version of
Leafnode is 1.9.19. Work is underway on a 2.0 release, which will add support
for local newsgroups, making Leafnode suitable for running a small news server
for local newsgroups. The 1.9.x versions don't
support this feature, though.It's important to remember that Leafnode was
designed as a news reader for small sites. It
doesn't scale well, meaning that as you add users and large numbers of
newsgroups, Leafnode's performance suffers. Leafnode works well for up to a few
dozen clients, but it's not very useable beyond that point. If you're
experiencing performance problems that are caused by a heavy server load, you
should seriously consider switching to INN or some other conventional news
server and obtaining a full news feed.Another problem with Leafnode is that it may drop messages if
it encounters a problem. This may result in posts that aren't posted to Usenet,
or in existing Usenet posts that aren't readable. Some fetchnews options attempt to work around
some of these problems, as described shortly, but you may lose posts if your
connection to your upstream news server is unreliable.
Configuring
Leafnode
Configuring Leafnode requires setting up three programs: The leafnode server itself, the fetchnews program, and texpire to expire old news. Functions
relating to all three programs are contained in a general configuration file,
but you'll need to set up each program to run in its own way. If you use a
Leafnode package from your Linux distribution, you shouldn't need to edit many
files to get it all running.
General
Configuration Settings
The main Leafnode configuration file is called config , and it's usually stored in /etc/leafnode . Aside from comments, which
begin with a pound sign ( # ),
this file consists of lines of the following form: parameter = value
A minimal Leafnode configuration needs to set just a couple of
parameters: server and expire . Other parameters are optional;
they take on reasonable default values if you don't set them. The more
important parameters are as follows: server
This parameter sets the name of your upstream news server, as in server = news.abigisp.net . You can
configure Leafnode to fetch news from multiple news servers by including more
than one server line. expire
This parameter sets the number of days Leafnode retains messages before
deleting them. username
If your upstream news server requires you to enter a username, specify it with
this parameter. password
If you need a password to access your upstream news server, enter it with this
parameter.WARNING
align=left border=0> Your password is stored in a plain text file, and so could
potentially be stolen. The default permissions on the config file in most distributions make
it accessible only to root , so
the risk is minimized. It is also sent unencrypted to the news server. If
possible, you shouldn't use the password for anything except access to your
news server.
port Most
news servers operate on port 119 (the default), but you can specify another
port with this parameter. nodesc
Most news servers provide a newsgroup descriptions file when asked for it. A
few don't, though. Leafnode works best with these when you use the nodesc = 1 parameter. timeout
When connecting to a news server, fetchnews
normally waits ten seconds, then stops trying. You can set another timeout interval
with this parameter. groupexpire
group.name If you
want to set different article retention intervals for different newsgroups, you
can adjust the value set via expire
for specific groups or collections of groups with this parameter. The group.name may contain wildcards, such
as comp.os.linux.* for the
entire comp.os.linux hierarchy. maxfetch
Leafnode limits the number of new articles it will fetch from any one group
with this option. Setting this value too low can cause problems, because it
might regularly fail to fetch all the new articles, and thus fall behind the
current postings. initialfetch
You can set a lower number of articles to fetch for a newly-subscribed group
with this parameter, the idea being that you might not want to fetch all the posts
in a new group from a server with retention of several days because this might
take a long time. delaybody
Leafnode normally fetches all new message headers and message bodies with each
run, within constraints such as those set by maxfetch
and other options. You can have Leafnode fetch only headers, however, and then
fetch message bodies only after a user has clicked on a message in a news
reader, indicating a desire to read the message. When an unfetched message is
read, the message body indicates that Leafnode has marked it for download.
After the next fetch, the message title appears again as an unread message,
which then contains the true message. Setting this parameter to 1 will delay your ability to read new
messages, but this option can greatly reduce the amount of data that must be
transferred. maxcrosspost
Leafnode offers this option as an anti-spam measure. It kills messages that
have been cross-posted to more than the specified number of groups. The default
is to accept unlimited cross-posting. maxage
Occasionally, misconfigured news servers repeatedly bounce the same messages
onto Usenet, resulting in massive numbers of repeat postings. Using this
parameter causes Leafnode to ignore messages that are more than a specified
number of days old. This might limit the severity of such problems. The default
is to not use this criterion. maxlines
You can have Leafnode reject messages that have more than the specified number
of lines. By default, this limit isn't used. minlines
You can have Leafnode reject messages that have fewer than the specified number
of lines. By default, this limit isn't used. maxbytes
You can have Leafnode reject messages that have more than the specified number
of bytes. By default, this limit isn't used. timeout_short
By default, Leafnode retrieves posts for two days after a newsgroup has been
opened accidentally. You can change this value with this parameter. timeout_long
By default, Leafnode retrieves posts for seven days after a newsgroup is no
longer being read. You can change this value with this parameter. timeout_active
Leafnode periodically refreshes its list of available newsgroups from the
upstream server. This parameter sets how frequently this occurs, in days. The
default is 90 days. filterfile
This parameter sets the path to the filter file, described in the upcoming
section, "
to use a filter file. hostname
Most news readers create message IDs for their messages, but if they don't,
Leafnode does it for them, using the hostname of the computer on which it runs.
If this hostname is inappropriate, you can change the value with this
parameter.These parameters set options that relate to all three of the
major Leafnode component programs ( leafnode ,
fetchnews , and texpire ). These programs don't have
separate configuration files, but they must be run in different ways.
Setting
Up the Server
As mentioned earlier, the leafnode
server program is designed to be run from a super server, such as inetd or xinetd .
This topic is covered in
the following: nntp stream tcp nowait news /usr/sbin/tcpd /usr/sbin/leafnode
Distributions that use xinetd
usually include an appropriate startup file in their Leafnode packages that go
in /etc/xinetd.d , so you
shouldn't need to create such a file. You might need to enable it, though.
Whether you use inetd or xinetd , chances are you'll need to restart
the super server before your Leafnode server will become available to your
clients. Once you've done this, the Leafnode server computer will respond to
requests from news readers as if it were running INN or some other full news
server package.WARNING
align=left border=0> Leafnode's main configuration file doesn't include
access-control features. You should add such controls to your xinetd or TCP Wrappers configuration to
prevent unwanted access to your Leafnode system.
Fetching News
A single run of the fetchnews
program will retrieve news from your upstream news server, assuming you've
configured the appropriate news server hostname in /etc/leafnode/config . The same process uploads any pending
messages to your upstream news server. (You can use the newsq command to see how many outgoing
messages you have waiting, as well as their titles, newsgroups, and senders.)
The first time you run fetchnews ,
chances are the operation will take some time, as the program will fetch the
active newsgroups list from the upstream server.The fetchnews
program accepts several arguments, which are as follows: -v This
option increases the verbosity of the program's output. You can increase the
number of v s, up to four (as in -vvvv ) to further increase the verbosity
of output. This can be a useful diagnostic tool when fetchnews isn't working as you expect. -x number If you ran into a problem
on the previous fetch operation, this option will attempt to re-fetch articles
up to number back. -l As
noted earlier, Leafnode supports fetching from multiple servers. Using this
option forces it to fetch news from just the first one. -n This
option causes Leafnode to not automatically unsubscribe from newsgroups that
aren't being read. -f If your
newsgroup list seems stale, you can force fetchnews
to update the list using this option. (The program does so automatically every
90 days, by default.) This operation can take some time, though. -P This
option causes fetchnews to post
articles it's accumulated in its outgoing queue without retrieving new ones.TIP
align=left border=0> Normally, you won't see your own posts in your Leafnode
newsgroups until you've called fetchnews
twice. If you call fetchnews
with its -P option prior to
calling fetchnews , your posts
will appear as soon as you make this dual call. The Leafnode 2.0 beta doesn't
suffer from the delayed appearance problem, so the workaround has no effect.
The real trick to fetchnews
operation is in determining when and how to run it. Two common options are to
run it as a cron job and to run it in a PPP dialup script, such as ppp-on-dialer (described in
Running fetchnews as a cron job
makes sense when you have a connection that's constantly active, or if you want
to have your computer automatically dial out and retrieve news when unattended,
such as early in the morning. How often you should do so is a matter of
personal preference and practical matters specific to your configuration and
your upstream provider's availability. Running fetchnews
as part of a PPP connect script ensures that you'll be able to read the latest
news soon after you connect to the Internet.
Expiring
Old News
The texpire
program peruses the news messages stored in the news spool directory and
deletes old messages according to default values or those set in /etc/leafnode/config . This task should be
performed on a regular basis to ensure that your hard disk doesn't overflow
with old news postings. The usual way to accomplish this task is to run texpire from a cron job on a daily basis.
Some distributions' Leafnode packages include an appropriate script that's
dropped in /etc/cron.daily or
some other location, but you shouldn't assume that your distribution maintainer
has seen to this detail; you should check for such a script and, if necessary,
create one or use the crontab
utility to do the job.When texpire runs, it expires
articles based on threads. (A thread is an
original posting and associated replies.) Specifically, texpire deletes a message only if the thread hasn't been read by local users in more
than the expire time. Thus, articles may be kept around for longer than you
might expect, if the thread in which they reside has been recently read by
Leafnode clients.Like fetchnews , texpire accepts one to four -v options to increase its verbosity. Another potentially important texpire option
is -f . Ordinarily, texpire relies upon the last-access dates that Linux stores with files to
determine when a thread has gone unread. Adding -f causes texpire to
ignore this information. You might do this if you regularly back up your news
spool directory with a program like tar , which modifies the
last-access date as part of its operation, causing texpire to erroneously
believe that messages are being read when they aren't.
Filtering Articles
Leafnode includes the capability to delete
messages that match arbitrary criteria based on the contents of the messages'
headers. For instance, suppose you read a newsgroup that's regularly disrupted
by a person who posts from the account obnoxious@annoying.edu .
This username will appear in the From header, so Leafnode can filter
messages based on this information. To tell it to do so, you must edit a filter
file, such as /etc/leafnode/filters , which contains filtering information in regular expression form. For
instance, to remove posts from obnoxious@annoying.edu , you might include
a line like the following: ^From:.*obnoxious@annoying\.edu
Each expression in this file begins with a
carat ( ^ ), then the name of the header line that's to be filtered ( From: , in this
case). The period and asterisk characters ( .* ) indicate that an
arbitrary number of characters may intervene. The string obnoxious@annoying can be represented directly, and so is; but the period has special
meaning, so the period in .edu must be escaped with a backslash ( \ ) character.NOTE
align=left border=0> This description barely scratches the
surface of what regular expressions can do. The "
Mail Protocol: SMTP, provides more information on regular expressions.
You must tell Leafnode where to find the
filter file you use. You do this with the filterfile parameter in /etc/leafnode/config , as described earlier. Although the filter file often goes in /etc/leafnode/filters , you can select any other filename you like.
