Using the default mirrors you can only select a release, such as 5 or 6. Furthermore, note the following from the CentOS FAQ:
Since all updates within a major release (CentOS 2, CentOS 3, CentOS 4) always upgrade to the latest version when updates are performed (thus mimicing upstream behavior), only the latest version is maintained in each main tree on the CentOS mirrors.
So you can't find a '5.5' mirror in the official list anyway (i.e. http://mirrors.melbourne.co.uk/sites/ftp.centos.org/centos/5.6/readme).
However, it *is* possible to do this yourself very easily with BoxGrinder.
- Set *default_repos: false* in your appliance definition
- Source a 5.5 mirror of the *base* and *updates* repositories (or download local copies), add them into your appliance as repos (see: http://boxgrinder.org/tutorials/how-to-use-local-repository/#Add_repository_to_your_appliance_definition)
Thank You, I'm understand