Sometimes I want to duplicate or reuse a Virtual Machine for another purpose. This week I had to start with a setup for a B2B communication for a client. So I pick one, duplicate them and change the particular hostname and corresponding network settings (/etc/hosts) to reflect the particular situation. So that I can communicate to the instance with its own host-alias.

It is not exactly necessary, but it is neat to have the hostname of the server changed to the particular situation. But if you have installed an Oracle 11g database, you'll encounter that you can't login at it anymore.
Some how the database checks the hostname and with the ip-address of the server its installed on.
I found the solution here in the doc, see paragraph 3.3.2.2. Network.

You'll have to make sure that the name of your host (see cat /etc/sysconfig/network) is in the /etc/hosts file with the ip address of the machine.
So my first network adapter is a host-only with a fixed address of 10.0.0.1. As such I installed the database. If I change my hostname to 'darwin-vce-soa', for instance then in the /etc/hosts there should be a line like:

10.0.0.1          darwin-vce-soa.darwin-it.local    darwin-vce-soa

Also make sure that you change the listner.ora and tnsnames.ora in $ORACLE_HOME/network/admin.

Oh, and if you are on a demo/development server, you may want to have password expiry turned off. See my blog-entry here.