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copied!<p>Before you get started, try running <code>hostname</code> and <code>hostname --fqdn</code> and take note of what the responses are.</p> <p>You can edit <code>/etc/hostname</code> and set a hostname, which will stick around after rebooting. You can force the hostname to be "reloaded" by using <code>hostname -F /etc/hostname</code> to read that value into the hostname. The bash prompt will change after you logout and login.</p> <p><strong>warning / note</strong>:<br> Yes, it is nice to have the hostname in the bash prompt set to something more useful than <code>ip-123-123-123-123</code> but I've decided to leave mine (at least for now) because it seems like a lot of things really count on having the hostname on ec2 instances set in a standard way. After editing <code>/etc/hostname</code> and changing the hostname to <code>webserver</code> a lot of the services seems to fail because the hostname would not resolve, and apache wouldn't start. Next I edited <code>/etc/hosts</code> and added in </p> <pre><code>127.0.0.1 webserver </code></pre> <p>as the second line. Apache would then start but complained that it couldn't find the FQDN. I confirmed that running <code>hostname --fqdn</code> no longer worked.</p> <p>Next I consulted <code>man hostname</code> and learned that while you can set the <code>hostname</code> it appears that the <code>FQDN</code> is what is returned via a DNS lookup. </p> <blockquote> <h3>THE FQDN</h3> <p>You can't change the FQDN (as returned by hostname --fqdn) or the DNS domain name (as returned by dnsdomainname) with this command. The FQDN of the system is the name that the resolver(3) returns for the host name.</p> <p>Technically: The FQDN is the name getaddrinfo(3) returns for the host name returned by gethostname(2). The DNS domain name is the part after the first dot.</p> <p>Therefore it depends on the configuration (usually in /etc/host.conf) how you can change it. Usually (if the hosts file is parsed before DNS or NIS) you can change it in /etc/hosts.</p> </blockquote> <p>I think it might be possible to set the system / fool the system into return the FQDN, something like <code>ip-123-123-123-123.ec2.internal</code> even though the hostname is <code>webserver</code> but at this point it started to seem like more trouble than it was worth, and that for me to have a nicer bash prompt might cause a lot software and configuration problems down the road and so I decided to give up.</p> <p>I also learned that a lot of amazon ec2 instances use something called <a href="https://help.ubuntu.com/community/CloudInit" rel="noreferrer">cloud-init</a>:</p> <blockquote> <p>cloud-init is the Ubuntu package that handles early initialization of a cloud instance. It is installed in the Ubuntu Cloud Images and also in the official Ubuntu images available on EC2.</p> <p>Some of the things it configures are:</p> <ul> <li>setting a default locale</li> <li>setting hostname</li> <li>generate ssh private keys</li> <li>adding ssh keys to user's .ssh/authorized_keys so they can log in</li> <li>setting up ephemeral mount points</li> </ul> <p>cloud-init's behavior can be configured via user-data. User-data can be given by the user at instance launch time. This is done via the --user-data or --user-data-file argument to ec2-run-instances</p> </blockquote> <p><a href="https://code.launchpad.net/~clint-fewbar/cloud-init/glusterfs-mount-example" rel="noreferrer">I also found this</a> which talks about how the hostname is configured with cloud-init:</p> <blockquote> <p>On EBS instances, a shutdown and later start would end up with a different IP address. </p> <p>In the case where the user has not modified /etc/hostname from its original value (seeded by metadata's 'local-hostname'), then cloud-init will again set the hostname and update /etc/hostname. </p> <p>In the case where the user has modified /etc/hostname, it will remain user managed. </p> <p>Additionally, if /etc/cloud/cloud.cfg contains 'preserve_hostname' value set to a True value, then /etc/hostname will not ever be touched.</p> </blockquote> <p>The interesting takeaway is that if you don't change the hostname the cloud-init package will keep it up to date for you.</p> <p>If someone else has a workaround or can address some of the issues mentioned and help reassure that nothing will break on ec2 instances because of changing the hostname I would be happy to hear it.</p>

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