Cloud computing ahs a few disadvantages, some of them are:
Security and privacy: The data in Ubuntu cloud have many instances with a third party which many users may not prefer. Cloud servers store sensitive information which must be protected at all costs. There is a vulnerability of unauthorized access.
Loss of control (dependency): In cloud computing the cloud service providers play a major role more maintenance and fixing of the cloud. Being a third party an organization has less control over it. And once a cloud is established migrating to another CSP is not an easy task.
Costs: Although in the long run cloud computing is cheap but being a new technology the improvements and research involved makes it quite expensive. To incorporate this technology many changes may be require including the development of software.
Integration and knowledge: As most of the functions are provided by a CSP getting to understand the system from an organizational point of view is tough. Also integration with existing systems is hard to achieve.