Problem

The following error appears in the atlassian-jira.log:

2011-03-16 18:20:03,021 ERROR [main] [net.sf.ehcache.Cache] <clinit> Unable to set localhost. This prevents creation of a GUID. Cause was: <hostname>: <hostname>
java.net.UnknownHostException: <hostname>: <hostname>
    at java.net.InetAddress.getLocalHost(InetAddress.java:1354)
    at net.sf.ehcache.Cache.<clinit>(Cache.java:145)

Cause

The local hostname (or COMPUTERNAME - Windows) that is running JIRA is not in the host file or is not resolvable via DNS lookup.

Resolution

Change the local hostname (or COMPUTERNAME in Windows) that is running JIRA to match the host file, or enter the local hostname into the hosts file.
windows

C:\Windows\System32\drivers\etc\hosts

linux/unix environments

/etc/hosts

We strongly recommend placing the hostname in the host file as fail-safe for DNS server failure.

Alternatively, make the hostname resolvable via DNS.