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Setting the hostname: FQDN or short name?

ayi

I’ve noticed that the “preferred” method of setting the system hostname is fundamentally different between Red Hat/CentOS and Debian/Ubuntu systems.
<a href="https://web.archive.org/web/20111129072841/http://www.centos.org/docs/5/html/5.2/Deployment_Guide/s2-sysconfig-network.html" rel="noopener nofollow ugc">CentOS documentation</a> and the <a href="https://web.archive.org/web/20120113152304/https://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/5/html/Deployment_Guide/ch-sysconfig.html#s2-sysconfig-network" rel="noopener nofollow ugc">RHEL deployment guide</a> say the hostname should be the FQDN:
<blockquote></blockquote>
<code>HOSTNAME=<value></code>, where <code><value></code> should be the Fully Qualified Domain 
Name (FQDN), such as <code>hostname.example.com</code>, but can be whatever 
hostname is necessary.
The <a href="https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/6/html/installation_guide/sn-netconfig-x86" rel="noopener nofollow ugc">RHEL install guide</a> is slightly more ambiguous:
<blockquote></blockquote>
Setup prompts you to supply a host name for this computer, either as a 
fully-qualified domain name (FQDN) in the format hostname.domainname 
or as a short host name in the format hostname.
<a href="https://web.archive.org/web/20111128083537/http://www.debian.org/doc/manuals/debian-reference/ch03.en.html#_the_hostname" rel="noopener nofollow ugc">The Debian reference</a> says the hostname should not use the FQDN:
<blockquote></blockquote>
3.5.5. The hostname
The kernel maintains the system hostname. The init script in runlevel 
S which is symlinked to “/etc/init.d/hostname.sh” sets the system 
hostname at boot time (using the hostname command) to the name stored 
in “/etc/hostname”. This file should contain only the system hostname, 
not a fully qualified domain name.
I haven’t seen any specific recommendations from IBM about which to use, but <a href="http://publib.boulder.ibm.com/infocenter/tivihelp/v10r1/index.jsp?topic=%2Fcom.ibm.tsam.doc_7.1%2Fc_prep_ms_for_aix.html" rel="noopener nofollow ugc">some software</a> seems to have a preference.
My questions:
<ul>
<li>
In a heterogeneous environment, is it better to use the vendor recommendation, or choose one and be consistent across all hosts?
</li>
<li>
What software have you encountered which is sensitive to whether the hostname is set to the FQDN or short name?
</li>
</ul>

ayi_2

I would choose a consistent approach across the entire environment. Both solutions work fine and will remain compatible with most applications. There is a difference in manageability, though.
I go with the short name as the HOSTNAME setting, and set the FQDN as the first column in <code>/etc/hosts</code> for the server’s IP, followed by the short name.
I have not encountered many software packages that enforce or display a preference between the two. I find the short name to be cleaner for some applications, specifically logging. Maybe I’ve been unlucky in seeing internal domains like <code>server.northside.chicago.rizzomanufacturing.com</code>. Who wants to see that in the logs or a shell prompt?
Sometimes, I’m involved in company acquisitions or restructuring where internal domains and/or subdomains change. I like using the short hostname in these cases because logging, kickstarts, printing, systems monitoring, etc. do not need full reconfiguration to account for the new domain names.
A typical RHEL/CentOS server setup for a server named “rizzo” with internal domain “<a href="http://ifp.com">ifp.com</a>”, would look like:
<pre><code class="lang-auto">/etc/sysconfig/network:
HOSTNAME=rizzo
...

</code></pre>
<ul>
<li></li>
</ul>
<pre><code class="lang-auto">/etc/hosts:
127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4
::1 localhost localhost.localdomain localhost6 localhost6.localdomain6

172.16.100.13 rizzo.ifp.com rizzo

</code></pre>
<ul>
<li></li>
</ul>
<pre><code class="lang-auto">[root@rizzo ~]# hostname
rizzo

</code></pre>
<ul>
<li></li>
</ul>
<pre><code class="lang-auto">/var/log/messages snippet:
Dec 15 10:10:13 rizzo proftpd[19675]: 172.16.100.13 (::ffff:206.15.236.182[::ffff:206.15.236.182]) - Preparing to
chroot to directory '/app/upload/GREEK'
Dec 15 10:10:51 rizzo proftpd[20660]: 172.16.100.13 (::ffff:12.28.170.2[::ffff:12.28.170.2]) - FTP session opened.
Dec 15 10:10:51 rizzo proftpd[20660]: 172.16.100.13 (::ffff:12.28.170.2[::ffff:12.28.170.2]) - Preparing to chroot
to directory '/app/upload/ftp/SRRID'

</code></pre>