So you are about to install leafnode, to communicate with the wide world. Not just via e-mail, to chosen people in your e-mail address book, but world-wide, via Usenet news.
Every message (mail or news) has a unique identifier in its header, the Message-ID. It looks roughly like an E-Mail address, <12345.67890@host.example.com>: it has a local and a domain part, separated by a @ sign, only that the local part of the Message-ID is different for different pieces of mail or news, while the local part of the mail is constant (unless you use something like TMDA), and the domain part is usually the name of the host that generated the Message-ID: your computer's name when you are sending mail or posting news.
Whenever a news server is offered a new news article for redistribution, it looks at the Message-ID to determine if it already has the article, to avoid double work, and to avoid that news articles run in circles.
Therefore, each message sent, mail or news, must have a unique Message-ID. If the Message-ID is not unique, because you use the same host name as somebody else, and you and the other person write an article at the same time, either article will be discarded by the server. Leafnode will tell you that the Message-ID of the article it is about to post was already in use upstream.
Please note that this problem is not leafnode-specific. Any software may suffer, but it's less prominent in mail, and it's difficult to see, because you're not getting a bounce back.
Well, it is probably the default name or domain that your OS vendor chose, like ``localhost.localdomain''. As such, it is not unique, but used on many computers, and therefore does not qualify as fully qualified domain name.
There are several ways to obtain one. See below on how to install your domain name.
telnet news.cis.dfn.de 119 authinfo user sixpack authinfo pass joe quit
Replace ``sixpack'' and ``joe'' by your login and password. After the ``authinfo pass'' line, you should see a line that reads:
281 Authentication accepted. (UID=00000)
If you get a 481 line, please retry, you may have mistyped user name or password. Correcting these lines with Backspace or Delete may also lead to failed logins. Retry with careful typing so that you do not need to correct your input.
00000 shall be replaced by your actual user ID.
Your hostname then is ID-00000.news.dfncis.de. DO MAKE SURE TO REPLACE THE NUMBER IN ID-00000 by the number the server told you in the UID= LINE.
Preferably, the host name is entered into your system configuration so that it is available globally, to your mailers and news readers should they desire to create a FQDN. How exactly the hostname is configured, depends on your system. SuSE Linux 7.3 reads it from FQHOSTNAME in /etc/rc.config, FreeBSD 4.6 reads it from hostname in /etc/rc.conf.
On many systems, you will have to put the fully qualified host name into /etc/hosts in addition to the place mentioned above, UNLESS it is listed in DNS. Leafnode will use the system resolver to qualify an unqualified hostname, which itself will then look at /etc/hosts first and then at DNS.
An /etc/hosts line might look like this:
192.168.0.1 abacus.mid.example.com abacus oldname
Keep the original name of the computer as an alias in case some other software relies on the old name.