Determine FQDN when hostname doesn’t give it

hostnamepuppet

In another question, I found that Puppet was generating certificates for my machine's FQDN but not the simple host name. In that example, kungfumaster was the hostname and was the value retrieved by running hostname. Puppet was generating certificates which specified the FQDN kungfumaster.domain.com.

How did Puppet determine that this was my FQDN? I have tried all of the following and not seen anything matching *.domain.com:

$ hostname -a && hostname -d && hostname --domain && hostname -f && \ 
    hostname --fqdn && hostname -A && hostname --long

kungfumaster
kungfumaster
kungfumaster 
kungfumaster

How can I get kungfumaster.domain.com from Bash? I've noticed that domain.com does in fact exist in /etc/resolv.conf, but I haven't been able to find it anywhere else.

I basically want to get the FQDN of the current machine as a string. The other solutions here on unix.se haven't worked for me. (ie: dnsdomainname, domainname, etc.)

Best Answer

It appears that under-the-hood, Puppet uses Facter to evaluate the domain names:

$ facter domain
domain.com
$ facter hostname
kungfumaster
$ facter fqdn
kungfumaster.domain.com

The answer is in the relevant Facter source code.

It does the following in order and uses the first one that appears to contain a domain name:

hostname -f
dnsdomainname
parsing resolv.conf for a "domain" or "search" entry

Related Solutions

`hostname` – host name or FQDN

Just the name as you already do. A hostname shouldn't contain any domainname.

The difference between hostname, hostname –fqdn, and hostname -A

hostname returns the configured hostname or nodename. In practice, it can either be a short name (in most configurations) or a long name (normally the FQDN in this case). The short name is given by hostname --short.

hostname --fqdn returns the FQDN, which is gethostbyname on the nodename (as returned by the uname system call, see uname(2) man page).

hostname -A is something obscure and non-intuitive. In particular, despite its name and description ("all FQDNs"), it doesn't give the standard FQDN, by design. Thus I would say: do not use it. One reason is that it misses valid IP addresses of the machine, such as 127.0.1.1, with which the FQDN may be associated in the /etc/hosts file (this is currently the default under Debian and Ubuntu, for instance). Another issue with the hostname -A method is that the reverse resolution of an IP address doesn't necessarily give a FQDN; it can just be a short name.

Concerning your problem with python, it may be a bug there. I don't know. I suggest that you try the following Perl script:

#!/usr/bin/env perl

use strict;
use POSIX;

my $nodename = (POSIX::uname)[1];
print "Nodename: $nodename\n";

my @ghbn = gethostbyname $nodename;
print "FQDN: $ghbn[0]\n";

$ghbn[0] !~ /\./ && $ghbn[1] =~ /(\S+\.\S+)/
  and print "Fixed FQDN from aliases: $1\n";

Best Answer

Related Solutions

`hostname` – host name or FQDN

The difference between hostname, hostname –fqdn, and hostname -A

Related Question