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I have a webserver running a number of websites.

When I ssh in, it gives me a tab name of username@localhost.localdomain, which is counterintuitive, making it seem like those tabs are on my localhost.

I would like to change the hostname, but I want to be sure that it won't break anything else.

So for what purposes does that hostname string get used, and how can I be sure that it won't affect any functioning systems?

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4 Answers

I believe the only thing that is supposed to directly accesses /etc/hostname is the startup script /etc/init.d/hostname.sh.

Your apache configuration may depend on the hostname being a certain thing. When you setup apache did you use IP addresses in your configuration or the name that was in /etc/hostname.

If you have a mail server setup it could also be using the name from /etc/hostname. Though localhost.localdomain is what is in /etc/hostname, then I suspect your email system is partly broken already.

I believe it should be pretty safe to change the file. Change the file, run /etc/init.d/hostname.sh and then restart any services you are running like apache. If there are issues the fix should just be a minor edit of a couple configuration files.

If you are really paranoid you could copy the production system into a VM, make the change in the VM and then see what breaks. If you don't already have a test environment now might be a good time to set one up.

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While the hostname is defined in /etc/hostname, many processes will use DNS and/or the hosts files to figure out the hostname. So you might try looking at /etc/hosts and also check the nameservers listed in /etc/resolv.conf to see what is defined.

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The problem you are encountering is likley in /etc/hosts. This is where addresses are looked up. There should be an entry there for your servers IP address. Fallback is to use the loopback address, localhost@localdomain.

See http://www.faqs.org/rfcs/rfc1178.html for best practices on naming your host. /etc/hostname is used to populate then name in in the kernel during starup. Put the unqualified name in /etc/hostname and run 'sudo /etc/init.d/hostname start'. Also add an entry for your hostname in /etc/hosts using the interface address in /etc/hosts.

The mail server should use /etc/mailname to determine its name. This should be a fully qualifed address suchas myhost.example.com.

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Depending on the configuring in your /etc/nssswitch.conf file you can use it for domainname resolution before calling out to a different system, normally DNS.

hosts:      files dns

That indication that first it should use the local files (/etc/hosts) and then query DNS.

So, normally, the system will route all hostname queries through /etc/hosts first, before querying DNS.

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