Cosmic Ray Study of the CMS Pixel Tracker

The pixel detector of the Compact Muon Solenoid (CMS) experiment consists of three barrel layers and two endcap disks at each side of the barrel section. The detector was installed in summer 2008, commissioned with the readout chip internal pulse generator, and used in cosmic ray trigger data taking in a 3.8~T magnetic field. Despite the excellent detector performance some problems arose after installation. In about a year we went through a complete and important sequence of steps that go from the insertion of the detector in CMS, calibration, running, extraction, maintenance, to the re-insertion, re-calibration and final running. In this paper a summary of the knowledge acquired during the first year of running will be presented. Currently 98.6\% of the whole pixel detector is fully functional and results on detector performance are found to be in line with the design specifications.