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Re: Why is Firefox such a beast??



On Sun, 2008-10-05 at 18:00 +0000, Beartooth wrote:
> FATAL: Could not determine fully qualified hostname.  Please set 
> 'visible_hostname'
> 
>
>         I don't know what a qualified hostname is, fully or not. 

There's plenty of places on the WWW that explain that, but here goes.

A "hostname" is the (generally) one-word name that you address your
machine by (the name associated with a numerical IP address).

e.g. localhost is the hostname associated with 127.0.0.1 - the local
loopback address (internal networking that doesn't leave the PC).

The same applies for associating a hostname with an IP address that can
be connected to from another PC on the network.  e.g. This PC is called
gonzales (since it was the fastest box on the LAN), I set that as its
hostname, and it's IP address is 192.168.1.11.

A fully-qualified domain name (FQDN) is the complete address, hostname
plus the domain name.  e.g. www.example.com.

Strictly speaking, it ends with a dot (representing the top of the
tree), though few people see that unless they're working with domain
name servers.  The dot means that it's the full address, otherwise its
(probably) a hostname, and the system will try and work out what domain
name should be appended to it, to turn it into a FQDN.

The process of working it out *CAN* be done like this.  I am "gonzales"
lookup this to find my IP, I find I am 192.168.1.11.  Okay, now lets
lookup 192.168.1.11 (a reverse lookup) to find my FQDN, and I get told
that I'm "gonzales.example.com.", and that's the end of that story.

However, if I'd queried 192.168.1.11 and been told that I'm
"gonzales.lan" (note the lack of a trailing dot), I'd know that's not a
FQDN, just a hostname (albeit one with a dot in it), so I'd go through
the query cycle again - find the IP for gonzales.lan, then find the
address associated with that IP, hopefully getting a FQDN.

This sort of thing can be a bit of a pain when someone sets up machines
with multiple names, that need to be stepped through to work out the
FQDN.  And this set of resolution steps (find the IP, find the name,
rinse, lather, repeat) is the process SSH goes through before allowing a
connection (checking that names and IPs match, in both directions).

ALTERNATIVELY:  Your network can be configured to prepend specific
domain names to hostnames.  So if a hostname is used (a name that
doesn't *END* with a dot), it automatically prepends the preferred
domain name to it.  See the "domain" and "search" parameters that are
used in the /etc/resolv.conf (man resolv.conf).  Basically "domain"
means providing one answer for a domain that you are part of, whereas
"search" allows you to give a list of domain names to try.

e.g. If I had example.com and example.net as search parameters, and I
did "ping www", my system would first see if it found an answer (finds
an IP address) for just "www", then "www.example.com", then
"www.example.net", in turn.  The first answer wins.

There's also configuration options for what constitutes the domain name
if there's multiple dots in it.  e.g. Given "mail.lan.example.com", the
domain could be lan.example.com or it could be example.com.  You can
configure whether the domain starts after the first dot, or after how
many dots.  The dividing line between what you consider to be a domain,
or a sub-domain, is up to how you want your network configuration.

In the simple case, the /etc/hosts file is used for resolving names, but
that involves putting the same hosts file on each machine on the
network.  I use a DNS server, which serves the same purpose, but on one
central server.

-- 
[tim localhost ~]$ uname -r
2.6.26.5-45.fc9.i686

Don't send private replies to my address, the mailbox is ignored.  I
read messages from the public lists.




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