Critical services in the LHC Computing

The LHC experiments (ALICE, ATLAS, CMS and LHCb) rely for the data acquisition, processing, distribution, analysis and simulation on complex computing systems, running using a variety of services, provided by the experiments, the Worldwide LHC Computing Grid and the different computing centres. These services range from the most basic (network, batch systems, file systems) to the mass storage services or the Grid information system, up to the different workload management systems, data catalogues and data transfer tools, often internally developed in the collaborations. In this contribution we review the status of the services most critical to the experiments by quantitatively measuring their readiness with respect to the start of the LHC operations. Shortcomings are identified and common recommendations are offered.