The cancel Message
The most widely known message is cancel, with which a user can cancel an article sent earlier. This effectively removes the article from the spool directories, if it exists. The cancel message is forwarded to all sites that receive news from the groups affected, regardless of whether the article has been seen already. This takes into account the possibility that the original article has been delayed over the cancellation message. Some news systems allow users to cancel other people's messages; this is, of course, a definite no-no.
newgroup and rmgroup
Two messages dealing with creation or removal of newsgroups are the newgroup and rmgroup messages. Newsgroups below the "usual" hierarchies may be created only after a discussion and voting has been held among Usenet readers. The rules applying to the alt hierarchy allow for something close to anarchy. For more information, see the regular postings in news.announce.newusers and news.announce.newgroups. Never send a newgroup or rmgroup message yourself unless you definitely know that you are allowed to.
The checkgroups Message
checkgroups messages are sent by news administrators to make all sites within a network synchronize their active files with the realities of Usenet. For example, commercial Internet Service Providers might send out such a message to their customers' sites. Once a month, the "official" checkgroups message for the major hierarchies is posted to comp.announce.newgroups by its moderator. However, it is posted as an ordinary article, not as a control message. To perform the checkgroups operation, save this article to a file, say /tmp/check, remove everything up to the beginning of the control message itself, and feed it to the checkgroups script using the following command:
# su news -c "/usr/lib/news/ctl/checkgroups" ‹ /tmp/check
This will update your newsgroups file from the new list of groups, adding the groups listed in localgroups. The old newsgroups file will be moved to newsgroups.bac. Note that posting the message locally rarely works, because inews, the command that accepts and posts articles from users, refuses to accept that large an article.
If C News finds mismatches between the checkgroups list and the active file, it produces a list of commands that would bring your site up to date and mails it to the news administrator.
The output typically looks like this:
From news Sun Jan 30 16:18:11 1994
Date: Sun, 30 Jan 94 16:18 MET
From: news (News Subsystem)
To: usenet
Subject: Problems with your active file
The following newsgroups are not valid and should be removed.
alt.ascii-art
bionet.molbio.gene-org
comp.windows.x.intrisics
de.answers
You can do this by executing the commands:
/usr/lib/news/maint/delgroup alt.ascii-art
/usr/lib/news/maint/delgroup bionet.molbio.gene-org
/usr/lib/news/maint/delgroup comp.windows.x.intrisics
/usr/lib/news/maint/delgroup de.answers
The following newsgroups were missing.
comp.binaries.cbm
comp.databases.rdb
comp.os.geos
comp.os.qnx
comp.unix.user-friendly
misc.legal.moderated
news.newsites
soc.culture.scientists
talk.politics.crypto
talk.politics.tibet
When you receive a message like this from your news system, don't believe it automatically. Depending on who sent the checkgroups message, it may lack a few groups or even entire hierarchies; you should be careful about removing any groups. If you find groups are listed as missing that you want to carry at your site, you have to add them using the addgroup script. Save the list of missing groups to a file and feed it to the following little script:
#!/bin/sh
#
WHOIAM=`whoami`
if [ "$WHOIAM" != "news" ]
then
echo "You must run $0 as user 'news'" >&2
exit 1
fi
#
cd /usr/lib/news
while read group; do
if grep -si "^$group[[:space:]].*moderated" newsgroup; then
mod=m
else
mod=y
fi
/usr/lib/news/maint/addgroup $group $mod
done
sendsys, version, and senduuname
Finally, there are three messages that can be used to find out about the network's topology. These are sendsys, version, and senduuname. They cause C News to return the sys file to the sender, as well as a software version string and the output of uuname, respectively. C News is very laconic about version messages; it returns a simple, unadorned C.
Again, you should never issue such a message unless you have made sure that it cannot leave your (regional) network. Replies to sendsys messages can quickly bring down a UUCP network.[131]
C News in an NFS Environment
A simple way to distribute news within a local network is to keep all news on a central host and export the relevant directories via NFS so that newsreaders may scan the articles directly. The overhead involved in retrieving and threading articles is significantly lower than NNTP. NNTP, on the other hand, wins in a heterogeneous network where equipment varies widely among hosts, or where users don't have equivalent accounts on the server machine.
When you use NFS, articles posted on a local host have to be forwarded to the central machine because accessing adminstrative files might otherwise expose the system to race conditions that leave the files inconsistent. Also, you might want to protect your news spool area by exporting it read-only, which also requires forwarding to the central machine.
C News handles this central machine configuration transparently to the user. When you post an article, your newsreader usually invokes inews to inject the article into the news system. This command runs a number of checks on the article, completes the header, and checks the file server in /etc/news. If this file exists and contains a hostname different from the local host's name, inews is invoked on that server host via rsh. Since the inews script uses a number of binary commands and support files from C News, you have to either have C News installed locally or mount the news software from the server.